-- Hoogle documentation, generated by Haddock -- See Hoogle, http://www.haskell.org/hoogle/ -- | Types, functions, and tools to manipulate the openSUSE distribution -- -- This library is a loose collection of types, functions, and tools that -- users and developers of the openSUSE Linux distribution might -- find useful. @package distribution-opensuse @version 1.1.4 module OpenSuse.Prelude.Parser module OpenSuse.Prelude.PrettyPrinting.Orphans instance Text.PrettyPrint.HughesPJClass.Pretty GHC.Num.Natural.Natural -- | This is simply a re-export of the standard library pretty -- with some orphan instances added for convenience. module OpenSuse.Prelude.PrettyPrinting module OpenSuse.Prelude -- | Append two lists, i.e., -- --

--   [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
--   [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
--

-- -- If the first list is not finite, the result is the first list. (++) :: [a] -> [a] -> [a] infixr 5 ++ -- | The value of seq a b is bottom if a is bottom, and -- otherwise equal to b. In other words, it evaluates the first -- argument a to weak head normal form (WHNF). seq is -- usually introduced to improve performance by avoiding unneeded -- laziness. -- -- A note on evaluation order: the expression seq a b does -- not guarantee that a will be evaluated before -- b. The only guarantee given by seq is that the both -- a and b will be evaluated before seq -- returns a value. In particular, this means that b may be -- evaluated before a. If you need to guarantee a specific order -- of evaluation, you must use the function pseq from the -- "parallel" package. seq :: forall {r :: RuntimeRep} a (b :: TYPE r). a -> b -> b infixr 0 `seq` -- | <math>. filter, applied to a predicate and a list, -- returns the list of those elements that satisfy the predicate; i.e., -- --

--   filter p xs = [ x | x <- xs, p x]
--

-- --

--   >>> filter odd [1, 2, 3]
--   [1,3]
--

filter :: (a -> Bool) -> [a] -> [a] -- | <math>. zip takes two lists and returns a list of -- corresponding pairs. -- --

--   >>> zip [1, 2] ['a', 'b']
--   [(1,'a'),(2,'b')]
--

-- -- If one input list is shorter than the other, excess elements of the -- longer list are discarded, even if one of the lists is infinite: -- --

--   >>> zip [1] ['a', 'b']
--   [(1,'a')]
--   
--   >>> zip [1, 2] ['a']
--   [(1,'a')]
--   
--   >>> zip [] [1..]
--   []
--   
--   >>> zip [1..] []
--   []
--

-- -- zip is right-lazy: -- --

--   >>> zip [] undefined
--   []
--   
--   >>> zip undefined []
--   *** Exception: Prelude.undefined
--   ...
--

-- -- zip is capable of list fusion, but it is restricted to its -- first list argument and its resulting list. zip :: [a] -> [b] -> [(a, b)] -- | The print function outputs a value of any printable type to the -- standard output device. Printable types are those that are instances -- of class Show; print converts values to strings for -- output using the show operation and adds a newline. -- -- For example, a program to print the first 20 integers and their powers -- of 2 could be written as: -- --

--   main = print ([(n, 2^n) | n <- [0..19]])
--

print :: Show a => a -> IO () -- | Extract the first component of a pair. fst :: (a, b) -> a -- | Extract the second component of a pair. snd :: (a, b) -> b -- | otherwise is defined as the value True. It helps to make -- guards more readable. eg. -- --

--   f x | x < 0     = ...
--       | otherwise = ...
--

otherwise :: Bool -- | <math>. map f xs is the list obtained by -- applying f to each element of xs, i.e., -- --

--   map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
--   map f [x1, x2, ...] == [f x1, f x2, ...]
--

-- --

--   >>> map (+1) [1, 2, 3]
--   [2,3,4]
--

map :: (a -> b) -> [a] -> [b] -- | Application operator. This operator is redundant, since ordinary -- application (f x) means the same as (f $ x). -- However, $ has low, right-associative binding precedence, so it -- sometimes allows parentheses to be omitted; for example: -- --

--   f $ g $ h x  =  f (g (h x))
--

-- -- It is also useful in higher-order situations, such as map -- ($ 0) xs, or zipWith ($) fs xs. -- -- Note that ($) is levity-polymorphic in its result -- type, so that foo $ True where foo :: Bool -> -- Int# is well-typed. ($) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b infixr 0 $ -- | general coercion from integral types fromIntegral :: (Integral a, Num b) => a -> b -- | general coercion to fractional types realToFrac :: (Real a, Fractional b) => a -> b -- | The Bounded class is used to name the upper and lower limits of -- a type. Ord is not a superclass of Bounded since types -- that are not totally ordered may also have upper and lower bounds. -- -- The Bounded class may be derived for any enumeration type; -- minBound is the first constructor listed in the data -- declaration and maxBound is the last. Bounded may also -- be derived for single-constructor datatypes whose constituent types -- are in Bounded. class Bounded a minBound :: Bounded a => a maxBound :: Bounded a => a -- | Class Enum defines operations on sequentially ordered types. -- -- The enumFrom... methods are used in Haskell's translation of -- arithmetic sequences. -- -- Instances of Enum may be derived for any enumeration type -- (types whose constructors have no fields). The nullary constructors -- are assumed to be numbered left-to-right by fromEnum from -- 0 through n-1. See Chapter 10 of the Haskell -- Report for more details. -- -- For any type that is an instance of class Bounded as well as -- Enum, the following should hold: -- --

The calls succ maxBound and pred -- minBound should result in a runtime error.
fromEnum and toEnum should give a runtime error if -- the result value is not representable in the result type. For example, -- toEnum 7 :: Bool is an error.
enumFrom and enumFromThen should be defined with an -- implicit bound, thus:

-- --

--   enumFrom     x   = enumFromTo     x maxBound
--   enumFromThen x y = enumFromThenTo x y bound
--     where
--       bound | fromEnum y >= fromEnum x = maxBound
--             | otherwise                = minBound
--

class Enum a -- | the successor of a value. For numeric types, succ adds 1. succ :: Enum a => a -> a -- | the predecessor of a value. For numeric types, pred subtracts -- 1. pred :: Enum a => a -> a -- | Convert from an Int. toEnum :: Enum a => Int -> a -- | Convert to an Int. It is implementation-dependent what -- fromEnum returns when applied to a value that is too large to -- fit in an Int. fromEnum :: Enum a => a -> Int -- | Used in Haskell's translation of [n..] with [n..] = -- enumFrom n, a possible implementation being enumFrom n = n : -- enumFrom (succ n). For example: -- --

```
enumFrom 4 :: [Integer] = [4,5,6,7,...]
```

enumFrom 6 :: [Int] = [6,7,8,9,...,maxBound ::
--   Int]

enumFrom :: Enum a => a -> [a] -- | Used in Haskell's translation of [n,n'..] with [n,n'..] = -- enumFromThen n n', a possible implementation being -- enumFromThen n n' = n : n' : worker (f x) (f x n'), -- worker s v = v : worker s (s v), x = fromEnum n' - -- fromEnum n and f n y | n > 0 = f (n - 1) (succ y) | n < -- 0 = f (n + 1) (pred y) | otherwise = y For example: -- --

enumFromThen 4 6 :: [Integer] = [4,6,8,10...]

enumFromThen 6 2 :: [Int] = [6,2,-2,-6,...,minBound ::
--   Int]

enumFromThen :: Enum a => a -> a -> [a] -- | Used in Haskell's translation of [n..m] with [n..m] = -- enumFromTo n m, a possible implementation being enumFromTo n -- m | n <= m = n : enumFromTo (succ n) m | otherwise = []. For -- example: -- --

```
enumFromTo 6 10 :: [Int] = [6,7,8,9,10]
```
```
enumFromTo 42 1 :: [Integer] = []
```

enumFromTo :: Enum a => a -> a -> [a] -- | Used in Haskell's translation of [n,n'..m] with [n,n'..m] -- = enumFromThenTo n n' m, a possible implementation being -- enumFromThenTo n n' m = worker (f x) (c x) n m, x = -- fromEnum n' - fromEnum n, c x = bool (>=) ((x -- 0) f n y | n > 0 = f (n - 1) (succ y) | n < 0 = f (n + -- 1) (pred y) | otherwise = y and worker s c v m | c v m = v : -- worker s c (s v) m | otherwise = [] For example: -- --

enumFromThenTo 4 2 -6 :: [Integer] =
--   [4,2,0,-2,-4,-6]

```
enumFromThenTo 6 8 2 :: [Int] = []
```

enumFromThenTo :: Enum a => a -> a -> a -> [a] -- | The Eq class defines equality (==) and inequality -- (/=). All the basic datatypes exported by the Prelude -- are instances of Eq, and Eq may be derived for any -- datatype whose constituents are also instances of Eq. -- -- The Haskell Report defines no laws for Eq. However, instances -- are encouraged to follow these properties: -- --

Reflexivity x == x = True
Symmetry x == y = y == x
Transitivity if x == y && y == z = -- True, then x == z = True
Extensionality if x == y = True and -- f is a function whose return type is an instance of -- Eq, then f x == f y = True
Negation x /= y = not (x == -- y)

-- -- Minimal complete definition: either == or /=. class Eq a (==) :: Eq a => a -> a -> Bool (/=) :: Eq a => a -> a -> Bool infix 4 == infix 4 /= -- | Trigonometric and hyperbolic functions and related functions. -- -- The Haskell Report defines no laws for Floating. However, -- (+), (*) and exp are -- customarily expected to define an exponential field and have the -- following properties: -- --

exp (a + b) = exp a * exp b
exp (fromInteger 0) = fromInteger 1

class Fractional a => Floating a pi :: Floating a => a exp :: Floating a => a -> a log :: Floating a => a -> a sqrt :: Floating a => a -> a (**) :: Floating a => a -> a -> a logBase :: Floating a => a -> a -> a sin :: Floating a => a -> a cos :: Floating a => a -> a tan :: Floating a => a -> a asin :: Floating a => a -> a acos :: Floating a => a -> a atan :: Floating a => a -> a sinh :: Floating a => a -> a cosh :: Floating a => a -> a tanh :: Floating a => a -> a asinh :: Floating a => a -> a acosh :: Floating a => a -> a atanh :: Floating a => a -> a infixr 8 ** -- | Fractional numbers, supporting real division. -- -- The Haskell Report defines no laws for Fractional. However, -- (+) and (*) are customarily expected -- to define a division ring and have the following properties: -- --

recip gives the multiplicative inverse x -- * recip x = recip x * x = fromInteger 1

-- -- Note that it isn't customarily expected that a type instance of -- Fractional implement a field. However, all instances in -- base do. class Num a => Fractional a -- | Fractional division. (/) :: Fractional a => a -> a -> a -- | Reciprocal fraction. recip :: Fractional a => a -> a -- | Conversion from a Rational (that is Ratio -- Integer). A floating literal stands for an application of -- fromRational to a value of type Rational, so such -- literals have type (Fractional a) => a. fromRational :: Fractional a => Rational -> a infixl 7 / -- | Integral numbers, supporting integer division. -- -- The Haskell Report defines no laws for Integral. However, -- Integral instances are customarily expected to define a -- Euclidean domain and have the following properties for the -- div/mod and quot/rem pairs, given suitable -- Euclidean functions f and g: -- --

x = y * quot x y + rem x y with rem x y -- = fromInteger 0 or g (rem x y) < g -- y
x = y * div x y + mod x y with mod x y -- = fromInteger 0 or f (mod x y) < f -- y

-- -- An example of a suitable Euclidean function, for Integer's -- instance, is abs. class (Real a, Enum a) => Integral a -- | integer division truncated toward zero quot :: Integral a => a -> a -> a -- | integer remainder, satisfying -- --

--   (x `quot` y)*y + (x `rem` y) == x
--

rem :: Integral a => a -> a -> a -- | integer division truncated toward negative infinity div :: Integral a => a -> a -> a -- | integer modulus, satisfying -- --

--   (x `div` y)*y + (x `mod` y) == x
--

mod :: Integral a => a -> a -> a -- | simultaneous quot and rem quotRem :: Integral a => a -> a -> (a, a) -- | simultaneous div and mod divMod :: Integral a => a -> a -> (a, a) -- | conversion to Integer toInteger :: Integral a => a -> Integer infixl 7 `rem` infixl 7 `quot` infixl 7 `mod` infixl 7 `div` -- | The Monad class defines the basic operations over a -- monad, a concept from a branch of mathematics known as -- category theory. From the perspective of a Haskell programmer, -- however, it is best to think of a monad as an abstract datatype -- of actions. Haskell's do expressions provide a convenient -- syntax for writing monadic expressions. -- -- Instances of Monad should satisfy the following: -- --

Left identity return a >>= k = k -- a
Right identity m >>= return = -- m
Associativity m >>= (\x -> k x -- >>= h) = (m >>= k) >>= -- h

-- -- Furthermore, the Monad and Applicative operations should -- relate as follows: -- --

```
pure = return
```

m1 <*> m2 = m1 >>= (x1 -> m2
--   >>= (x2 -> return (x1 x2)))

-- -- The above laws imply: -- --

```
fmap f xs = xs >>= return .
--   f
```
```
(>>) = (*>)
```

-- -- and that pure and (<*>) satisfy the applicative -- functor laws. -- -- The instances of Monad for lists, Maybe and IO -- defined in the Prelude satisfy these laws. class Applicative m => Monad (m :: Type -> Type) -- | Sequentially compose two actions, passing any value produced by the -- first as an argument to the second. -- -- 'as >>= bs' can be understood as the do -- expression -- --

--   do a <- as
--      bs a
--

(>>=) :: Monad m => m a -> (a -> m b) -> m b -- | Sequentially compose two actions, discarding any value produced by the -- first, like sequencing operators (such as the semicolon) in imperative -- languages. -- -- 'as >> bs' can be understood as the do -- expression -- --

--   do as
--      bs
--

(>>) :: Monad m => m a -> m b -> m b -- | Inject a value into the monadic type. return :: Monad m => a -> m a infixl 1 >>= infixl 1 >> -- | A type f is a Functor if it provides a function fmap -- which, given any types a and b lets you apply any -- function from (a -> b) to turn an f a into an -- f b, preserving the structure of f. Furthermore -- f needs to adhere to the following: -- --

Identity fmap id == id
Composition fmap (f . g) == fmap f . -- fmap g

-- -- Note, that the second law follows from the free theorem of the type -- fmap and the first law, so you need only check that the former -- condition holds. class Functor (f :: Type -> Type) -- | fmap is used to apply a function of type (a -> b) -- to a value of type f a, where f is a functor, to produce a -- value of type f b. Note that for any type constructor with -- more than one parameter (e.g., Either), only the last type -- parameter can be modified with fmap (e.g., b in -- `Either a b`). -- -- Some type constructors with two parameters or more have a -- Bifunctor instance that allows both the last and the -- penultimate parameters to be mapped over. -- --

Examples

-- -- Convert from a Maybe Int to a Maybe String -- using show: -- --

--   >>> fmap show Nothing
--   Nothing
--   
--   >>> fmap show (Just 3)
--   Just "3"
--

-- -- Convert from an Either Int Int to an Either Int -- String using show: -- --

--   >>> fmap show (Left 17)
--   Left 17
--   
--   >>> fmap show (Right 17)
--   Right "17"
--

-- -- Double each element of a list: -- --

--   >>> fmap (*2) [1,2,3]
--   [2,4,6]
--

-- -- Apply even to the second element of a pair: -- --

--   >>> fmap even (2,2)
--   (2,True)
--

-- -- It may seem surprising that the function is only applied to the last -- element of the tuple compared to the list example above which applies -- it to every element in the list. To understand, remember that tuples -- are type constructors with multiple type parameters: a tuple of 3 -- elements (a,b,c) can also be written (,,) a b c and -- its Functor instance is defined for Functor ((,,) a -- b) (i.e., only the third parameter is free to be mapped over with -- fmap). -- -- It explains why fmap can be used with tuples containing -- values of different types as in the following example: -- --

--   >>> fmap even ("hello", 1.0, 4)
--   ("hello",1.0,True)
--

fmap :: Functor f => (a -> b) -> f a -> f b -- | Replace all locations in the input with the same value. The default -- definition is fmap . const, but this may be -- overridden with a more efficient version. (<$) :: Functor f => a -> f b -> f a infixl 4 <$ -- | Basic numeric class. -- -- The Haskell Report defines no laws for Num. However, -- (+) and (*) are customarily expected -- to define a ring and have the following properties: -- --

Associativity of (+) (x + y) + -- z = x + (y + z)
Commutativity of (+) x + y -- = y + x
fromInteger 0 is the additive -- identity x + fromInteger 0 = x
negate gives the additive inverse x + -- negate x = fromInteger 0
Associativity of (*) (x * y) * -- z = x * (y * z)
fromInteger 1 is the multiplicative -- identity x * fromInteger 1 = x and -- fromInteger 1 * x = x
Distributivity of (*) with respect to -- (+) a * (b + c) = (a * b) + (a * -- c) and (b + c) * a = (b * a) + (c * a)

-- -- Note that it isn't customarily expected that a type instance of -- both Num and Ord implement an ordered ring. Indeed, in -- base only Integer and Rational do. class Num a (+) :: Num a => a -> a -> a (-) :: Num a => a -> a -> a (*) :: Num a => a -> a -> a -- | Unary negation. negate :: Num a => a -> a -- | Absolute value. abs :: Num a => a -> a -- | Sign of a number. The functions abs and signum should -- satisfy the law: -- --

--   abs x * signum x == x
--

-- -- For real numbers, the signum is either -1 (negative), -- 0 (zero) or 1 (positive). signum :: Num a => a -> a -- | Conversion from an Integer. An integer literal represents the -- application of the function fromInteger to the appropriate -- value of type Integer, so such literals have type -- (Num a) => a. fromInteger :: Num a => Integer -> a infixl 7 * infixl 6 + infixl 6 - -- | The Ord class is used for totally ordered datatypes. -- -- Instances of Ord can be derived for any user-defined datatype -- whose constituent types are in Ord. The declared order of the -- constructors in the data declaration determines the ordering in -- derived Ord instances. The Ordering datatype allows a -- single comparison to determine the precise ordering of two objects. -- -- Ord, as defined by the Haskell report, implements a total order -- and has the following properties: -- --

Comparability x <= y || y <= x = -- True
Transitivity if x <= y && y <= -- z = True, then x <= z = True
Reflexivity x <= x = True
Antisymmetry if x <= y && y <= -- x = True, then x == y = True

-- -- The following operator interactions are expected to hold: -- --

x >= y = y <= x
x < y = x <= y && x /= y
x > y = y < x
x < y = compare x y == LT
x > y = compare x y == GT
x == y = compare x y == EQ
min x y == if x <= y then x else y = True
max x y == if x >= y then x else y = True

-- -- Note that (7.) and (8.) do not require min and -- max to return either of their arguments. The result is merely -- required to equal one of the arguments in terms of (==). -- -- Minimal complete definition: either compare or <=. -- Using compare can be more efficient for complex types. class Eq a => Ord a compare :: Ord a => a -> a -> Ordering (<) :: Ord a => a -> a -> Bool (<=) :: Ord a => a -> a -> Bool (>) :: Ord a => a -> a -> Bool (>=) :: Ord a => a -> a -> Bool max :: Ord a => a -> a -> a min :: Ord a => a -> a -> a infix 4 < infix 4 <= infix 4 > infix 4 >= -- | Parsing of Strings, producing values. -- -- Derived instances of Read make the following assumptions, which -- derived instances of Show obey: -- --

If the constructor is defined to be an infix operator, then the -- derived Read instance will parse only infix applications of the -- constructor (not the prefix form).
Associativity is not used to reduce the occurrence of parentheses, -- although precedence may be.
If the constructor is defined using record syntax, the derived -- Read will parse only the record-syntax form, and furthermore, -- the fields must be given in the same order as the original -- declaration.
The derived Read instance allows arbitrary Haskell -- whitespace between tokens of the input string. Extra parentheses are -- also allowed.

-- -- For example, given the declarations -- --

--   infixr 5 :^:
--   data Tree a =  Leaf a  |  Tree a :^: Tree a
--

-- -- the derived instance of Read in Haskell 2010 is equivalent to -- --

--   instance (Read a) => Read (Tree a) where
--   
--           readsPrec d r =  readParen (d > app_prec)
--                            (\r -> [(Leaf m,t) |
--                                    ("Leaf",s) <- lex r,
--                                    (m,t) <- readsPrec (app_prec+1) s]) r
--   
--                         ++ readParen (d > up_prec)
--                            (\r -> [(u:^:v,w) |
--                                    (u,s) <- readsPrec (up_prec+1) r,
--                                    (":^:",t) <- lex s,
--                                    (v,w) <- readsPrec (up_prec+1) t]) r
--   
--             where app_prec = 10
--                   up_prec = 5
--

-- -- Note that right-associativity of :^: is unused. -- -- The derived instance in GHC is equivalent to -- --

--   instance (Read a) => Read (Tree a) where
--   
--           readPrec = parens $ (prec app_prec $ do
--                                    Ident "Leaf" <- lexP
--                                    m <- step readPrec
--                                    return (Leaf m))
--   
--                        +++ (prec up_prec $ do
--                                    u <- step readPrec
--                                    Symbol ":^:" <- lexP
--                                    v <- step readPrec
--                                    return (u :^: v))
--   
--             where app_prec = 10
--                   up_prec = 5
--   
--           readListPrec = readListPrecDefault
--

-- -- Why do both readsPrec and readPrec exist, and why does -- GHC opt to implement readPrec in derived Read instances -- instead of readsPrec? The reason is that readsPrec is -- based on the ReadS type, and although ReadS is mentioned -- in the Haskell 2010 Report, it is not a very efficient parser data -- structure. -- -- readPrec, on the other hand, is based on a much more efficient -- ReadPrec datatype (a.k.a "new-style parsers"), but its -- definition relies on the use of the RankNTypes language -- extension. Therefore, readPrec (and its cousin, -- readListPrec) are marked as GHC-only. Nevertheless, it is -- recommended to use readPrec instead of readsPrec -- whenever possible for the efficiency improvements it brings. -- -- As mentioned above, derived Read instances in GHC will -- implement readPrec instead of readsPrec. The default -- implementations of readsPrec (and its cousin, readList) -- will simply use readPrec under the hood. If you are writing a -- Read instance by hand, it is recommended to write it like so: -- --

--   instance Read T where
--     readPrec     = ...
--     readListPrec = readListPrecDefault
--

class Read a -- | attempts to parse a value from the front of the string, returning a -- list of (parsed value, remaining string) pairs. If there is no -- successful parse, the returned list is empty. -- -- Derived instances of Read and Show satisfy the -- following: -- --

(x,"") is an element of (readsPrec d -- (showsPrec d x "")).

-- -- That is, readsPrec parses the string produced by -- showsPrec, and delivers the value that showsPrec started -- with. readsPrec :: Read a => Int -> ReadS a -- | The method readList is provided to allow the programmer to give -- a specialised way of parsing lists of values. For example, this is -- used by the predefined Read instance of the Char type, -- where values of type String should be are expected to use -- double quotes, rather than square brackets. readList :: Read a => ReadS [a] class (Num a, Ord a) => Real a -- | the rational equivalent of its real argument with full precision toRational :: Real a => a -> Rational -- | Efficient, machine-independent access to the components of a -- floating-point number. class (RealFrac a, Floating a) => RealFloat a -- | a constant function, returning the radix of the representation (often -- 2) floatRadix :: RealFloat a => a -> Integer -- | a constant function, returning the number of digits of -- floatRadix in the significand floatDigits :: RealFloat a => a -> Int -- | a constant function, returning the lowest and highest values the -- exponent may assume floatRange :: RealFloat a => a -> (Int, Int) -- | The function decodeFloat applied to a real floating-point -- number returns the significand expressed as an Integer and an -- appropriately scaled exponent (an Int). If -- decodeFloat x yields (m,n), then x -- is equal in value to m*b^^n, where b is the -- floating-point radix, and furthermore, either m and -- n are both zero or else b^(d-1) <= abs m < -- b^d, where d is the value of floatDigits -- x. In particular, decodeFloat 0 = (0,0). If the -- type contains a negative zero, also decodeFloat (-0.0) = -- (0,0). The result of decodeFloat x is -- unspecified if either of isNaN x or -- isInfinite x is True. decodeFloat :: RealFloat a => a -> (Integer, Int) -- | encodeFloat performs the inverse of decodeFloat in the -- sense that for finite x with the exception of -0.0, -- uncurry encodeFloat (decodeFloat x) = x. -- encodeFloat m n is one of the two closest -- representable floating-point numbers to m*b^^n (or -- ±Infinity if overflow occurs); usually the closer, but if -- m contains too many bits, the result may be rounded in the -- wrong direction. encodeFloat :: RealFloat a => Integer -> Int -> a -- | exponent corresponds to the second component of -- decodeFloat. exponent 0 = 0 and for finite -- nonzero x, exponent x = snd (decodeFloat x) -- + floatDigits x. If x is a finite floating-point -- number, it is equal in value to significand x * b ^^ -- exponent x, where b is the floating-point radix. -- The behaviour is unspecified on infinite or NaN values. exponent :: RealFloat a => a -> Int -- | The first component of decodeFloat, scaled to lie in the open -- interval (-1,1), either 0.0 or of absolute -- value >= 1/b, where b is the floating-point -- radix. The behaviour is unspecified on infinite or NaN -- values. significand :: RealFloat a => a -> a -- | multiplies a floating-point number by an integer power of the radix scaleFloat :: RealFloat a => Int -> a -> a -- | True if the argument is an IEEE "not-a-number" (NaN) value isNaN :: RealFloat a => a -> Bool -- | True if the argument is an IEEE infinity or negative infinity isInfinite :: RealFloat a => a -> Bool -- | True if the argument is too small to be represented in -- normalized format isDenormalized :: RealFloat a => a -> Bool -- | True if the argument is an IEEE negative zero isNegativeZero :: RealFloat a => a -> Bool -- | True if the argument is an IEEE floating point number isIEEE :: RealFloat a => a -> Bool -- | a version of arctangent taking two real floating-point arguments. For -- real floating x and y, atan2 y x -- computes the angle (from the positive x-axis) of the vector from the -- origin to the point (x,y). atan2 y x returns -- a value in the range [-pi, pi]. It follows the -- Common Lisp semantics for the origin when signed zeroes are supported. -- atan2 y 1, with y in a type that is -- RealFloat, should return the same value as atan -- y. A default definition of atan2 is provided, but -- implementors can provide a more accurate implementation. atan2 :: RealFloat a => a -> a -> a -- | Extracting components of fractions. class (Real a, Fractional a) => RealFrac a -- | The function properFraction takes a real fractional number -- x and returns a pair (n,f) such that x = -- n+f, and: -- --

n is an integral number with the same sign as x; -- and
f is a fraction with the same type and sign as -- x, and with absolute value less than 1.

-- -- The default definitions of the ceiling, floor, -- truncate and round functions are in terms of -- properFraction. properFraction :: (RealFrac a, Integral b) => a -> (b, a) -- | truncate x returns the integer nearest x -- between zero and x truncate :: (RealFrac a, Integral b) => a -> b -- | round x returns the nearest integer to x; the -- even integer if x is equidistant between two integers round :: (RealFrac a, Integral b) => a -> b -- | ceiling x returns the least integer not less than -- x ceiling :: (RealFrac a, Integral b) => a -> b -- | floor x returns the greatest integer not greater than -- x floor :: (RealFrac a, Integral b) => a -> b -- | Conversion of values to readable Strings. -- -- Derived instances of Show have the following properties, which -- are compatible with derived instances of Read: -- --

The result of show is a syntactically correct Haskell -- expression containing only constants, given the fixity declarations in -- force at the point where the type is declared. It contains only the -- constructor names defined in the data type, parentheses, and spaces. -- When labelled constructor fields are used, braces, commas, field -- names, and equal signs are also used.
If the constructor is defined to be an infix operator, then -- showsPrec will produce infix applications of the -- constructor.
the representation will be enclosed in parentheses if the -- precedence of the top-level constructor in x is less than -- d (associativity is ignored). Thus, if d is -- 0 then the result is never surrounded in parentheses; if -- d is 11 it is always surrounded in parentheses, -- unless it is an atomic expression.
If the constructor is defined using record syntax, then -- show will produce the record-syntax form, with the fields given -- in the same order as the original declaration.

-- -- For example, given the declarations -- --

--   infixr 5 :^:
--   data Tree a =  Leaf a  |  Tree a :^: Tree a
--

-- -- the derived instance of Show is equivalent to -- --

--   instance (Show a) => Show (Tree a) where
--   
--          showsPrec d (Leaf m) = showParen (d > app_prec) $
--               showString "Leaf " . showsPrec (app_prec+1) m
--            where app_prec = 10
--   
--          showsPrec d (u :^: v) = showParen (d > up_prec) $
--               showsPrec (up_prec+1) u .
--               showString " :^: "      .
--               showsPrec (up_prec+1) v
--            where up_prec = 5
--

-- -- Note that right-associativity of :^: is ignored. For example, -- --

show (Leaf 1 :^: Leaf 2 :^: Leaf 3) produces the -- string "Leaf 1 :^: (Leaf 2 :^: Leaf 3)".

class Show a -- | Convert a value to a readable String. -- -- showsPrec should satisfy the law -- --

--   showsPrec d x r ++ s  ==  showsPrec d x (r ++ s)
--

-- -- Derived instances of Read and Show satisfy the -- following: -- --

(x,"") is an element of (readsPrec d -- (showsPrec d x "")).

-- -- That is, readsPrec parses the string produced by -- showsPrec, and delivers the value that showsPrec started -- with. showsPrec :: Show a => Int -> a -> ShowS -- | A specialised variant of showsPrec, using precedence context -- zero, and returning an ordinary String. show :: Show a => a -> String -- | The method showList is provided to allow the programmer to give -- a specialised way of showing lists of values. For example, this is -- used by the predefined Show instance of the Char type, -- where values of type String should be shown in double quotes, -- rather than between square brackets. showList :: Show a => [a] -> ShowS -- | When a value is bound in do-notation, the pattern on the left -- hand side of <- might not match. In this case, this class -- provides a function to recover. -- -- A Monad without a MonadFail instance may only be used in -- conjunction with pattern that always match, such as newtypes, tuples, -- data types with only a single data constructor, and irrefutable -- patterns (~pat). -- -- Instances of MonadFail should satisfy the following law: -- fail s should be a left zero for >>=, -- --

--   fail s >>= f  =  fail s
--

-- -- If your Monad is also MonadPlus, a popular definition is -- --

--   fail _ = mzero
--

class Monad m => MonadFail (m :: Type -> Type) -- | A functor with application, providing operations to -- --

embed pure expressions (pure), and
sequence computations and combine their results (<*> -- and liftA2).

-- -- A minimal complete definition must include implementations of -- pure and of either <*> or liftA2. If it -- defines both, then they must behave the same as their default -- definitions: -- --

--   (<*>) = liftA2 id
--

-- --

--   liftA2 f x y = f <$> x <*> y
--

-- -- Further, any definition must satisfy the following: -- --

Identity
```
pure id <*> v =
--   v
```

Composition

pure (.) <*> u
--   <*> v <*> w = u <*> (v
--   <*> w)

Homomorphism
```
pure f <*>
--   pure x = pure (f x)
```
Interchange
```
u <*> pure y =
--   pure ($ y) <*> u
```

-- -- The other methods have the following default definitions, which may be -- overridden with equivalent specialized implementations: -- --

```
u *> v = (id <$ u)
--   <*> v
```
```
u <* v = liftA2 const u v
```

-- -- As a consequence of these laws, the Functor instance for -- f will satisfy -- --

```
fmap f x = pure f <*> x
```

-- -- It may be useful to note that supposing -- --

--   forall x y. p (q x y) = f x . g y
--

-- -- it follows from the above that -- --

--   liftA2 p (liftA2 q u v) = liftA2 f u . liftA2 g v
--

-- -- If f is also a Monad, it should satisfy -- --

```
pure = return
```

m1 <*> m2 = m1 >>= (x1 -> m2
--   >>= (x2 -> return (x1 x2)))

```
(*>) = (>>)
```

-- -- (which implies that pure and <*> satisfy the -- applicative functor laws). class Functor f => Applicative (f :: Type -> Type) -- | Lift a value. pure :: Applicative f => a -> f a -- | Sequential application. -- -- A few functors support an implementation of <*> that is -- more efficient than the default one. -- --

Example

-- -- Used in combination with (<$>), -- (<*>) can be used to build a record. -- --

--   >>> data MyState = MyState {arg1 :: Foo, arg2 :: Bar, arg3 :: Baz}
--

-- --

--   >>> produceFoo :: Applicative f => f Foo
--

-- --

--   >>> produceBar :: Applicative f => f Bar
--   
--   >>> produceBaz :: Applicative f => f Baz
--

-- --

--   >>> mkState :: Applicative f => f MyState
--   
--   >>> mkState = MyState <$> produceFoo <*> produceBar <*> produceBaz
--

(<*>) :: Applicative f => f (a -> b) -> f a -> f b -- | Sequence actions, discarding the value of the first argument. -- --

Examples

-- -- If used in conjunction with the Applicative instance for Maybe, -- you can chain Maybe computations, with a possible "early return" in -- case of Nothing. -- --

--   >>> Just 2 *> Just 3
--   Just 3
--

-- --

--   >>> Nothing *> Just 3
--   Nothing
--

-- -- Of course a more interesting use case would be to have effectful -- computations instead of just returning pure values. -- --

--   >>> import Data.Char
--   
--   >>> import Text.ParserCombinators.ReadP
--   
--   >>> let p = string "my name is " *> munch1 isAlpha <* eof
--   
--   >>> readP_to_S p "my name is Simon"
--   [("Simon","")]
--

(*>) :: Applicative f => f a -> f b -> f b -- | Sequence actions, discarding the value of the second argument. (<*) :: Applicative f => f a -> f b -> f a infixl 4 <* infixl 4 *> infixl 4 <*> -- | The Foldable class represents data structures that can be reduced to a -- summary value one element at a time. Strict left-associative folds are -- a good fit for space-efficient reduction, while lazy right-associative -- folds are a good fit for corecursive iteration, or for folds that -- short-circuit after processing an initial subsequence of the -- structure's elements. -- -- Instances can be derived automatically by enabling the -- DeriveFoldable extension. For example, a derived instance for -- a binary tree might be: -- --

--   {-# LANGUAGE DeriveFoldable #-}
--   data Tree a = Empty
--               | Leaf a
--               | Node (Tree a) a (Tree a)
--       deriving Foldable
--

-- -- A more detailed description can be found in the Overview -- section of Data.Foldable#overview. -- -- For the class laws see the Laws section of -- Data.Foldable#laws. class Foldable (t :: TYPE LiftedRep -> Type) -- | Map each element of the structure into a monoid, and combine the -- results with (<>). This fold is -- right-associative and lazy in the accumulator. For strict -- left-associative folds consider foldMap' instead. -- --

Examples

-- -- Basic usage: -- --

--   >>> foldMap Sum [1, 3, 5]
--   Sum {getSum = 9}
--

-- --

--   >>> foldMap Product [1, 3, 5]
--   Product {getProduct = 15}
--

-- --

--   >>> foldMap (replicate 3) [1, 2, 3]
--   [1,1,1,2,2,2,3,3,3]
--

-- -- When a Monoid's (<>) is lazy in its second -- argument, foldMap can return a result even from an unbounded -- structure. For example, lazy accumulation enables -- Data.ByteString.Builder to efficiently serialise large data -- structures and produce the output incrementally: -- --

--   >>> import qualified Data.ByteString.Lazy as L
--   
--   >>> import qualified Data.ByteString.Builder as B
--   
--   >>> let bld :: Int -> B.Builder; bld i = B.intDec i <> B.word8 0x20
--   
--   >>> let lbs = B.toLazyByteString $ foldMap bld [0..]
--   
--   >>> L.take 64 lbs
--   "0 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24"
--

foldMap :: (Foldable t, Monoid m) => (a -> m) -> t a -> m -- | Right-associative fold of a structure, lazy in the accumulator. -- -- In the case of lists, foldr, when applied to a binary operator, -- a starting value (typically the right-identity of the operator), and a -- list, reduces the list using the binary operator, from right to left: -- --

--   foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
--

-- -- Note that since the head of the resulting expression is produced by an -- application of the operator to the first element of the list, given an -- operator lazy in its right argument, foldr can produce a -- terminating expression from an unbounded list. -- -- For a general Foldable structure this should be semantically -- identical to, -- --

--   foldr f z = foldr f z . toList
--

-- --

Examples

-- -- Basic usage: -- --

--   >>> foldr (||) False [False, True, False]
--   True
--

-- --

--   >>> foldr (||) False []
--   False
--

-- --

--   >>> foldr (\c acc -> acc ++ [c]) "foo" ['a', 'b', 'c', 'd']
--   "foodcba"
--

-- --

Infinite structures

-- -- ⚠️ Applying foldr to infinite structures usually doesn't -- terminate. -- -- It may still terminate under one of the following conditions: -- --

the folding function is short-circuiting
the folding function is lazy on its second argument

-- --

Short-circuiting

-- -- (||) short-circuits on True values, so the -- following terminates because there is a True value finitely far -- from the left side: -- --

--   >>> foldr (||) False (True : repeat False)
--   True
--

-- -- But the following doesn't terminate: -- --

--   >>> foldr (||) False (repeat False ++ [True])
--   * Hangs forever *
--

-- --

Laziness in the second argument

-- -- Applying foldr to infinite structures terminates when the -- operator is lazy in its second argument (the initial accumulator is -- never used in this case, and so could be left undefined, but -- [] is more clear): -- --

--   >>> take 5 $ foldr (\i acc -> i : fmap (+3) acc) [] (repeat 1)
--   [1,4,7,10,13]
--

foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b -- | Left-associative fold of a structure, lazy in the accumulator. This is -- rarely what you want, but can work well for structures with efficient -- right-to-left sequencing and an operator that is lazy in its left -- argument. -- -- In the case of lists, foldl, when applied to a binary operator, -- a starting value (typically the left-identity of the operator), and a -- list, reduces the list using the binary operator, from left to right: -- --

--   foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn
--

-- -- Note that to produce the outermost application of the operator the -- entire input list must be traversed. Like all left-associative folds, -- foldl will diverge if given an infinite list. -- -- If you want an efficient strict left-fold, you probably want to use -- foldl' instead of foldl. The reason for this is that the -- latter does not force the inner results (e.g. z `f` x1 -- in the above example) before applying them to the operator (e.g. to -- (`f` x2)). This results in a thunk chain <math> -- elements long, which then must be evaluated from the outside-in. -- -- For a general Foldable structure this should be semantically -- identical to: -- --

--   foldl f z = foldl f z . toList
--

-- --

Examples

-- -- The first example is a strict fold, which in practice is best -- performed with foldl'. -- --

--   >>> foldl (+) 42 [1,2,3,4]
--   52
--

-- -- Though the result below is lazy, the input is reversed before -- prepending it to the initial accumulator, so corecursion begins only -- after traversing the entire input string. -- --

--   >>> foldl (\acc c -> c : acc) "abcd" "efgh"
--   "hgfeabcd"
--

-- -- A left fold of a structure that is infinite on the right cannot -- terminate, even when for any finite input the fold just returns the -- initial accumulator: -- --

--   >>> foldl (\a _ -> a) 0 $ repeat 1
--   * Hangs forever *
--

-- -- WARNING: When it comes to lists, you always want to use either -- foldl' or foldr instead. foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b -- | A variant of foldr that has no base case, and thus may only be -- applied to non-empty structures. -- -- This function is non-total and will raise a runtime exception if the -- structure happens to be empty. -- --

Examples

-- -- Basic usage: -- --

--   >>> foldr1 (+) [1..4]
--   10
--

-- --

--   >>> foldr1 (+) []
--   Exception: Prelude.foldr1: empty list
--

-- --

--   >>> foldr1 (+) Nothing
--   *** Exception: foldr1: empty structure
--

-- --

--   >>> foldr1 (-) [1..4]
--   -2
--

-- --

--   >>> foldr1 (&&) [True, False, True, True]
--   False
--

-- --

--   >>> foldr1 (||) [False, False, True, True]
--   True
--

-- --

--   >>> foldr1 (+) [1..]
--   * Hangs forever *
--

foldr1 :: Foldable t => (a -> a -> a) -> t a -> a -- | A variant of foldl that has no base case, and thus may only be -- applied to non-empty structures. -- -- This function is non-total and will raise a runtime exception if the -- structure happens to be empty. -- --

--   foldl1 f = foldl1 f . toList
--

-- --

Examples

-- -- Basic usage: -- --

--   >>> foldl1 (+) [1..4]
--   10
--

-- --

--   >>> foldl1 (+) []
--   *** Exception: Prelude.foldl1: empty list
--

-- --

--   >>> foldl1 (+) Nothing
--   *** Exception: foldl1: empty structure
--

-- --

--   >>> foldl1 (-) [1..4]
--   -8
--

-- --

--   >>> foldl1 (&&) [True, False, True, True]
--   False
--

-- --

--   >>> foldl1 (||) [False, False, True, True]
--   True
--

-- --

--   >>> foldl1 (+) [1..]
--   * Hangs forever *
--

foldl1 :: Foldable t => (a -> a -> a) -> t a -> a -- | Test whether the structure is empty. The default implementation is -- Left-associative and lazy in both the initial element and the -- accumulator. Thus optimised for structures where the first element can -- be accessed in constant time. Structures where this is not the case -- should have a non-default implementation. -- --

Examples

-- -- Basic usage: -- --

--   >>> null []
--   True
--

-- --

--   >>> null [1]
--   False
--

-- -- null is expected to terminate even for infinite structures. The -- default implementation terminates provided the structure is bounded on -- the left (there is a leftmost element). -- --

--   >>> null [1..]
--   False
--

null :: Foldable t => t a -> Bool -- | Returns the size/length of a finite structure as an Int. The -- default implementation just counts elements starting with the -- leftmost. Instances for structures that can compute the element count -- faster than via element-by-element counting, should provide a -- specialised implementation. -- --

Examples

-- -- Basic usage: -- --

--   >>> length []
--   0
--

-- --

--   >>> length ['a', 'b', 'c']
--   3
--   
--   >>> length [1..]
--   * Hangs forever *
--

length :: Foldable t => t a -> Int -- | Does the element occur in the structure? -- -- Note: elem is often used in infix form. -- --

Examples

-- -- Basic usage: -- --

--   >>> 3 `elem` []
--   False
--

-- --

--   >>> 3 `elem` [1,2]
--   False
--

-- --

--   >>> 3 `elem` [1,2,3,4,5]
--   True
--

-- -- For infinite structures, the default implementation of elem -- terminates if the sought-after value exists at a finite distance from -- the left side of the structure: -- --

--   >>> 3 `elem` [1..]
--   True
--

-- --

--   >>> 3 `elem` ([4..] ++ [3])
--   * Hangs forever *
--

elem :: (Foldable t, Eq a) => a -> t a -> Bool -- | The largest element of a non-empty structure. -- -- This function is non-total and will raise a runtime exception if the -- structure happens to be empty. A structure that supports random access -- and maintains its elements in order should provide a specialised -- implementation to return the maximum in faster than linear time. -- --

Examples

-- -- Basic usage: -- --

--   >>> maximum [1..10]
--   10
--

-- --

--   >>> maximum []
--   *** Exception: Prelude.maximum: empty list
--

-- --

--   >>> maximum Nothing
--   *** Exception: maximum: empty structure
--

-- -- WARNING: This function is partial for possibly-empty structures like -- lists. maximum :: (Foldable t, Ord a) => t a -> a -- | The least element of a non-empty structure. -- -- This function is non-total and will raise a runtime exception if the -- structure happens to be empty. A structure that supports random access -- and maintains its elements in order should provide a specialised -- implementation to return the minimum in faster than linear time. -- --

Examples

-- -- Basic usage: -- --

--   >>> minimum [1..10]
--   1
--

-- --

--   >>> minimum []
--   *** Exception: Prelude.minimum: empty list
--

-- --

--   >>> minimum Nothing
--   *** Exception: minimum: empty structure
--

-- -- WARNING: This function is partial for possibly-empty structures like -- lists. minimum :: (Foldable t, Ord a) => t a -> a -- | The sum function computes the sum of the numbers of a -- structure. -- --

Examples

-- -- Basic usage: -- --

--   >>> sum []
--   0
--

-- --

--   >>> sum [42]
--   42
--

-- --

--   >>> sum [1..10]
--   55
--

-- --

--   >>> sum [4.1, 2.0, 1.7]
--   7.8
--

-- --

--   >>> sum [1..]
--   * Hangs forever *
--

sum :: (Foldable t, Num a) => t a -> a -- | The product function computes the product of the numbers of a -- structure. -- --

Examples

-- -- Basic usage: -- --

--   >>> product []
--   1
--

-- --

--   >>> product [42]
--   42
--

-- --

--   >>> product [1..10]
--   3628800
--

-- --

--   >>> product [4.1, 2.0, 1.7]
--   13.939999999999998
--

-- --

--   >>> product [1..]
--   * Hangs forever *
--

product :: (Foldable t, Num a) => t a -> a infix 4 `elem` -- | Functors representing data structures that can be transformed to -- structures of the same shape by performing an -- Applicative (or, therefore, Monad) action on each -- element from left to right. -- -- A more detailed description of what same shape means, the -- various methods, how traversals are constructed, and example advanced -- use-cases can be found in the Overview section of -- Data.Traversable#overview. -- -- For the class laws see the Laws section of -- Data.Traversable#laws. class (Functor t, Foldable t) => Traversable (t :: Type -> Type) -- | Map each element of a structure to an action, evaluate these actions -- from left to right, and collect the results. For a version that -- ignores the results see traverse_. -- --

Examples

-- -- Basic usage: -- -- In the first two examples we show each evaluated action mapping to the -- output structure. -- --

--   >>> traverse Just [1,2,3,4]
--   Just [1,2,3,4]
--

-- --

--   >>> traverse id [Right 1, Right 2, Right 3, Right 4]
--   Right [1,2,3,4]
--

-- -- In the next examples, we show that Nothing and Left -- values short circuit the created structure. -- --

--   >>> traverse (const Nothing) [1,2,3,4]
--   Nothing
--

-- --

--   >>> traverse (\x -> if odd x then Just x else Nothing)  [1,2,3,4]
--   Nothing
--

-- --

--   >>> traverse id [Right 1, Right 2, Right 3, Right 4, Left 0]
--   Left 0
--

traverse :: (Traversable t, Applicative f) => (a -> f b) -> t a -> f (t b) -- | Evaluate each action in the structure from left to right, and collect -- the results. For a version that ignores the results see -- sequenceA_. -- --

Examples

-- -- Basic usage: -- -- For the first two examples we show sequenceA fully evaluating a a -- structure and collecting the results. -- --

--   >>> sequenceA [Just 1, Just 2, Just 3]
--   Just [1,2,3]
--

-- --

--   >>> sequenceA [Right 1, Right 2, Right 3]
--   Right [1,2,3]
--

-- -- The next two example show Nothing and Just will short -- circuit the resulting structure if present in the input. For more -- context, check the Traversable instances for Either and -- Maybe. -- --

--   >>> sequenceA [Just 1, Just 2, Just 3, Nothing]
--   Nothing
--

-- --

--   >>> sequenceA [Right 1, Right 2, Right 3, Left 4]
--   Left 4
--

sequenceA :: (Traversable t, Applicative f) => t (f a) -> f (t a) -- | Map each element of a structure to a monadic action, evaluate these -- actions from left to right, and collect the results. For a version -- that ignores the results see mapM_. -- --

Examples

-- -- mapM is literally a traverse with a type signature -- restricted to Monad. Its implementation may be more efficient -- due to additional power of Monad. mapM :: (Traversable t, Monad m) => (a -> m b) -> t a -> m (t b) -- | Evaluate each monadic action in the structure from left to right, and -- collect the results. For a version that ignores the results see -- sequence_. -- --

Examples

-- -- Basic usage: -- -- The first two examples are instances where the input and and output of -- sequence are isomorphic. -- --

--   >>> sequence $ Right [1,2,3,4]
--   [Right 1,Right 2,Right 3,Right 4]
--

-- --

--   >>> sequence $ [Right 1,Right 2,Right 3,Right 4]
--   Right [1,2,3,4]
--

-- -- The following examples demonstrate short circuit behavior for -- sequence. -- --

--   >>> sequence $ Left [1,2,3,4]
--   Left [1,2,3,4]
--

-- --

--   >>> sequence $ [Left 0, Right 1,Right 2,Right 3,Right 4]
--   Left 0
--

sequence :: (Traversable t, Monad m) => t (m a) -> m (t a) -- | The class of semigroups (types with an associative binary operation). -- -- Instances should satisfy the following: -- --

Associativity x <> (y <> z) = -- (x <> y) <> z

class Semigroup a -- | The class of monoids (types with an associative binary operation that -- has an identity). Instances should satisfy the following: -- --

Right identity x <> mempty = -- x
Left identity mempty <> x = -- x
Associativity x <> (y <> z) = -- (x <> y) <> z (Semigroup -- law)
Concatenation mconcat = foldr -- (<>) mempty

-- -- The method names refer to the monoid of lists under concatenation, but -- there are many other instances. -- -- Some types can be viewed as a monoid in more than one way, e.g. both -- addition and multiplication on numbers. In such cases we often define -- newtypes and make those instances of Monoid, e.g. -- Sum and Product. -- -- NOTE: Semigroup is a superclass of Monoid since -- base-4.11.0.0. class Semigroup a => Monoid a -- | Identity of mappend -- --

--   >>> "Hello world" <> mempty
--   "Hello world"
--

mempty :: Monoid a => a -- | An associative operation -- -- NOTE: This method is redundant and has the default -- implementation mappend = (<>) since -- base-4.11.0.0. Should it be implemented manually, since -- mappend is a synonym for (<>), it is expected that -- the two functions are defined the same way. In a future GHC release -- mappend will be removed from Monoid. mappend :: Monoid a => a -> a -> a -- | Fold a list using the monoid. -- -- For most types, the default definition for mconcat will be -- used, but the function is included in the class definition so that an -- optimized version can be provided for specific types. -- --

--   >>> mconcat ["Hello", " ", "Haskell", "!"]
--   "Hello Haskell!"
--

mconcat :: Monoid a => [a] -> a data Bool False :: Bool True :: Bool -- | A String is a list of characters. String constants in Haskell -- are values of type String. -- -- See Data.List for operations on lists. type String = [Char] -- | The character type Char is an enumeration whose values -- represent Unicode (or equivalently ISO/IEC 10646) code points (i.e. -- characters, see http://www.unicode.org/ for details). This set -- extends the ISO 8859-1 (Latin-1) character set (the first 256 -- characters), which is itself an extension of the ASCII character set -- (the first 128 characters). A character literal in Haskell has type -- Char. -- -- To convert a Char to or from the corresponding Int value -- defined by Unicode, use toEnum and fromEnum from the -- Enum class respectively (or equivalently ord and -- chr). data Char -- | Double-precision floating point numbers. It is desirable that this -- type be at least equal in range and precision to the IEEE -- double-precision type. data Double -- | Single-precision floating point numbers. It is desirable that this -- type be at least equal in range and precision to the IEEE -- single-precision type. data Float -- | A fixed-precision integer type with at least the range [-2^29 .. -- 2^29-1]. The exact range for a given implementation can be -- determined by using minBound and maxBound from the -- Bounded class. data Int -- | Arbitrary precision integers. In contrast with fixed-size integral -- types such as Int, the Integer type represents the -- entire infinite range of integers. -- -- Integers are stored in a kind of sign-magnitude form, hence do not -- expect two's complement form when using bit operations. -- -- If the value is small (fit into an Int), IS constructor -- is used. Otherwise Integer and IN constructors are used -- to store a BigNat representing respectively the positive or the -- negative value magnitude. -- -- Invariant: Integer and IN are used iff value doesn't fit -- in IS data Integer -- | The Maybe type encapsulates an optional value. A value of type -- Maybe a either contains a value of type a -- (represented as Just a), or it is empty (represented -- as Nothing). Using Maybe is a good way to deal with -- errors or exceptional cases without resorting to drastic measures such -- as error. -- -- The Maybe type is also a monad. It is a simple kind of error -- monad, where all errors are represented by Nothing. A richer -- error monad can be built using the Either type. data Maybe a Nothing :: Maybe a Just :: a -> Maybe a data Ordering LT :: Ordering EQ :: Ordering GT :: Ordering -- | Arbitrary-precision rational numbers, represented as a ratio of two -- Integer values. A rational number may be constructed using the -- % operator. type Rational = Ratio Integer -- | A value of type IO a is a computation which, when -- performed, does some I/O before returning a value of type a. -- -- There is really only one way to "perform" an I/O action: bind it to -- Main.main in your program. When your program is run, the I/O -- will be performed. It isn't possible to perform I/O from an arbitrary -- function, unless that function is itself in the IO monad and -- called at some point, directly or indirectly, from Main.main. -- -- IO is a monad, so IO actions can be combined using -- either the do-notation or the >> and >>= -- operations from the Monad class. data IO a -- | A Word is an unsigned integral type, with the same size as -- Int. data Word -- | The Either type represents values with two possibilities: a -- value of type Either a b is either Left -- a or Right b. -- -- The Either type is sometimes used to represent a value which is -- either correct or an error; by convention, the Left constructor -- is used to hold an error value and the Right constructor is -- used to hold a correct value (mnemonic: "right" also means "correct"). -- --

Examples

-- -- The type Either String Int is the type -- of values which can be either a String or an Int. The -- Left constructor can be used only on Strings, and the -- Right constructor can be used only on Ints: -- --

--   >>> let s = Left "foo" :: Either String Int
--   
--   >>> s
--   Left "foo"
--   
--   >>> let n = Right 3 :: Either String Int
--   
--   >>> n
--   Right 3
--   
--   >>> :type s
--   s :: Either String Int
--   
--   >>> :type n
--   n :: Either String Int
--

-- -- The fmap from our Functor instance will ignore -- Left values, but will apply the supplied function to values -- contained in a Right: -- --

--   >>> let s = Left "foo" :: Either String Int
--   
--   >>> let n = Right 3 :: Either String Int
--   
--   >>> fmap (*2) s
--   Left "foo"
--   
--   >>> fmap (*2) n
--   Right 6
--

-- -- The Monad instance for Either allows us to chain -- together multiple actions which may fail, and fail overall if any of -- the individual steps failed. First we'll write a function that can -- either parse an Int from a Char, or fail. -- --

--   >>> import Data.Char ( digitToInt, isDigit )
--   
--   >>> :{
--       let parseEither :: Char -> Either String Int
--           parseEither c
--             | isDigit c = Right (digitToInt c)
--             | otherwise = Left "parse error"
--   
--   >>> :}
--

-- -- The following should work, since both '1' and '2' -- can be parsed as Ints. -- --

--   >>> :{
--       let parseMultiple :: Either String Int
--           parseMultiple = do
--             x <- parseEither '1'
--             y <- parseEither '2'
--             return (x + y)
--   
--   >>> :}
--

-- --

--   >>> parseMultiple
--   Right 3
--

-- -- But the following should fail overall, since the first operation where -- we attempt to parse 'm' as an Int will fail: -- --

--   >>> :{
--       let parseMultiple :: Either String Int
--           parseMultiple = do
--             x <- parseEither 'm'
--             y <- parseEither '2'
--             return (x + y)
--   
--   >>> :}
--

-- --

--   >>> parseMultiple
--   Left "parse error"
--

data Either a b Left :: a -> Either a b Right :: b -> Either a b -- | An infix synonym for fmap. -- -- The name of this operator is an allusion to $. Note the -- similarities between their types: -- --

--    ($)  ::              (a -> b) ->   a ->   b
--   (<$>) :: Functor f => (a -> b) -> f a -> f b
--

-- -- Whereas $ is function application, <$> is function -- application lifted over a Functor. -- --

Examples

-- -- Convert from a Maybe Int to a Maybe -- String using show: -- --

--   >>> show <$> Nothing
--   Nothing
--   
--   >>> show <$> Just 3
--   Just "3"
--

-- -- Convert from an Either Int Int to an -- Either Int String using show: -- --

--   >>> show <$> Left 17
--   Left 17
--   
--   >>> show <$> Right 17
--   Right "17"
--

-- -- Double each element of a list: -- --

--   >>> (*2) <$> [1,2,3]
--   [2,4,6]
--

-- -- Apply even to the second element of a pair: -- --

--   >>> even <$> (2,2)
--   (2,True)
--

(<$>) :: Functor f => (a -> b) -> f a -> f b infixl 4 <$> -- | const x is a unary function which evaluates to x for -- all inputs. -- --

--   >>> const 42 "hello"
--   42
--

-- --

--   >>> map (const 42) [0..3]
--   [42,42,42,42]
--

const :: a -> b -> a -- | Function composition. (.) :: (b -> c) -> (a -> b) -> a -> c infixr 9 . -- | Identity function. -- --

--   id x = x
--

id :: a -> a -- | The shows functions return a function that prepends the -- output String to an existing String. This allows -- constant-time concatenation of results using function composition. type ShowS = String -> String -- | Map each element of a structure to a monadic action, evaluate these -- actions from left to right, and ignore the results. For a version that -- doesn't ignore the results see mapM. -- -- mapM_ is just like traverse_, but specialised to monadic -- actions. mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m () -- | The read function reads input from a string, which must be -- completely consumed by the input process. read fails with an -- error if the parse is unsuccessful, and it is therefore -- discouraged from being used in real applications. Use readMaybe -- or readEither for safe alternatives. -- --

--   >>> read "123" :: Int
--   123
--

-- --

--   >>> read "hello" :: Int
--   *** Exception: Prelude.read: no parse
--

read :: Read a => String -> a -- | The computation writeFile file str function writes the -- string str, to the file file. writeFile :: FilePath -> String -> IO () -- | The readLn function combines getLine and readIO. readLn :: Read a => IO a -- | The readIO function is similar to read except that it -- signals parse failure to the IO monad instead of terminating -- the program. readIO :: Read a => String -> IO a -- | The readFile function reads a file and returns the contents of -- the file as a string. The file is read lazily, on demand, as with -- getContents. readFile :: FilePath -> IO String -- | The same as putStr, but adds a newline character. putStrLn :: String -> IO () -- | Write a string to the standard output device (same as hPutStr -- stdout). putStr :: String -> IO () -- | Write a character to the standard output device (same as -- hPutChar stdout). putChar :: Char -> IO () -- | The interact function takes a function of type -- String->String as its argument. The entire input from the -- standard input device is passed to this function as its argument, and -- the resulting string is output on the standard output device. interact :: (String -> String) -> IO () -- | Read a line from the standard input device (same as hGetLine -- stdin). getLine :: IO String -- | The getContents operation returns all user input as a single -- string, which is read lazily as it is needed (same as -- hGetContents stdin). getContents :: IO String -- | Read a character from the standard input device (same as -- hGetChar stdin). getChar :: IO Char -- | The computation appendFile file str function appends -- the string str, to the file file. -- -- Note that writeFile and appendFile write a literal -- string to a file. To write a value of any printable type, as with -- print, use the show function to convert the value to a -- string first. -- --

--   main = appendFile "squares" (show [(x,x*x) | x <- [0,0.1..2]])
--

appendFile :: FilePath -> String -> IO () -- | Raise an IOException in the IO monad. ioError :: IOError -> IO a -- | File and directory names are values of type String, whose -- precise meaning is operating system dependent. Files can be opened, -- yielding a handle which can then be used to operate on the contents of -- that file. type FilePath = String -- | The Haskell 2010 type for exceptions in the IO monad. Any I/O -- operation may raise an IOException instead of returning a -- result. For a more general type of exception, including also those -- that arise in pure code, see Exception. -- -- In Haskell 2010, this is an opaque type. type IOError = IOException -- | Construct an IOException value with a string describing the -- error. The fail method of the IO instance of the -- Monad class raises a userError, thus: -- --

--   instance Monad IO where
--     ...
--     fail s = ioError (userError s)
--

userError :: String -> IOError -- | Evaluate each monadic action in the structure from left to right, and -- ignore the results. For a version that doesn't ignore the results see -- sequence. -- -- sequence_ is just like sequenceA_, but specialised to -- monadic actions. sequence_ :: (Foldable t, Monad m) => t (m a) -> m () -- | or returns the disjunction of a container of Bools. For the -- result to be False, the container must be finite; True, -- however, results from a True value finitely far from the left -- end. -- --

Examples

-- -- Basic usage: -- --

--   >>> or []
--   False
--

-- --

--   >>> or [True]
--   True
--

-- --

--   >>> or [False]
--   False
--

-- --

--   >>> or [True, True, False]
--   True
--

-- --

--   >>> or (True : repeat False) -- Infinite list [True,False,False,False,...
--   True
--

-- --

--   >>> or (repeat False)
--   * Hangs forever *
--

or :: Foldable t => t Bool -> Bool -- | notElem is the negation of elem. -- --

Examples

-- -- Basic usage: -- --

--   >>> 3 `notElem` []
--   True
--

-- --

--   >>> 3 `notElem` [1,2]
--   True
--

-- --

--   >>> 3 `notElem` [1,2,3,4,5]
--   False
--

-- -- For infinite structures, notElem terminates if the value exists -- at a finite distance from the left side of the structure: -- --

--   >>> 3 `notElem` [1..]
--   False
--

-- --

--   >>> 3 `notElem` ([4..] ++ [3])
--   * Hangs forever *
--

notElem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 `notElem` -- | Map a function over all the elements of a container and concatenate -- the resulting lists. -- --

Examples

-- -- Basic usage: -- --

--   >>> concatMap (take 3) [[1..], [10..], [100..], [1000..]]
--   [1,2,3,10,11,12,100,101,102,1000,1001,1002]
--

-- --

--   >>> concatMap (take 3) (Just [1..])
--   [1,2,3]
--

concatMap :: Foldable t => (a -> [b]) -> t a -> [b] -- | The concatenation of all the elements of a container of lists. -- --

Examples

-- -- Basic usage: -- --

--   >>> concat (Just [1, 2, 3])
--   [1,2,3]
--

-- --

--   >>> concat (Left 42)
--   []
--

-- --

--   >>> concat [[1, 2, 3], [4, 5], [6], []]
--   [1,2,3,4,5,6]
--

concat :: Foldable t => t [a] -> [a] -- | Determines whether any element of the structure satisfies the -- predicate. -- --

Examples

-- -- Basic usage: -- --

--   >>> any (> 3) []
--   False
--

-- --

--   >>> any (> 3) [1,2]
--   False
--

-- --

--   >>> any (> 3) [1,2,3,4,5]
--   True
--

-- --

--   >>> any (> 3) [1..]
--   True
--

-- --

--   >>> any (> 3) [0, -1..]
--   * Hangs forever *
--

any :: Foldable t => (a -> Bool) -> t a -> Bool -- | and returns the conjunction of a container of Bools. For the -- result to be True, the container must be finite; False, -- however, results from a False value finitely far from the left -- end. -- --

Examples

-- -- Basic usage: -- --

--   >>> and []
--   True
--

-- --

--   >>> and [True]
--   True
--

-- --

--   >>> and [False]
--   False
--

-- --

--   >>> and [True, True, False]
--   False
--

-- --

--   >>> and (False : repeat True) -- Infinite list [False,True,True,True,...
--   False
--

-- --

--   >>> and (repeat True)
--   * Hangs forever *
--

and :: Foldable t => t Bool -> Bool -- | Determines whether all elements of the structure satisfy the -- predicate. -- --

Examples

-- -- Basic usage: -- --

--   >>> all (> 3) []
--   True
--

-- --

--   >>> all (> 3) [1,2]
--   False
--

-- --

--   >>> all (> 3) [1,2,3,4,5]
--   False
--

-- --

--   >>> all (> 3) [1..]
--   False
--

-- --

--   >>> all (> 3) [4..]
--   * Hangs forever *
--

all :: Foldable t => (a -> Bool) -> t a -> Bool -- | words breaks a string up into a list of words, which were -- delimited by white space. -- --

--   >>> words "Lorem ipsum\ndolor"
--   ["Lorem","ipsum","dolor"]
--

words :: String -> [String] -- | unwords is an inverse operation to words. It joins words -- with separating spaces. -- --

--   >>> unwords ["Lorem", "ipsum", "dolor"]
--   "Lorem ipsum dolor"
--

unwords :: [String] -> String -- | unlines is an inverse operation to lines. It joins -- lines, after appending a terminating newline to each. -- --

--   >>> unlines ["Hello", "World", "!"]
--   "Hello\nWorld\n!\n"
--

unlines :: [String] -> String -- | lines breaks a string up into a list of strings at newline -- characters. The resulting strings do not contain newlines. -- -- Note that after splitting the string at newline characters, the last -- part of the string is considered a line even if it doesn't end with a -- newline. For example, -- --

--   >>> lines ""
--   []
--

-- --

--   >>> lines "\n"
--   [""]
--

-- --

--   >>> lines "one"
--   ["one"]
--

-- --

--   >>> lines "one\n"
--   ["one"]
--

-- --

--   >>> lines "one\n\n"
--   ["one",""]
--

-- --

--   >>> lines "one\ntwo"
--   ["one","two"]
--

-- --

--   >>> lines "one\ntwo\n"
--   ["one","two"]
--

-- -- Thus lines s contains at least as many elements as -- newlines in s. lines :: String -> [String] -- | equivalent to readsPrec with a precedence of 0. reads :: Read a => ReadS a -- | Case analysis for the Either type. If the value is -- Left a, apply the first function to a; if it -- is Right b, apply the second function to b. -- --

Examples

-- -- We create two values of type Either String -- Int, one using the Left constructor and another -- using the Right constructor. Then we apply "either" the -- length function (if we have a String) or the "times-two" -- function (if we have an Int): -- --

--   >>> let s = Left "foo" :: Either String Int
--   
--   >>> let n = Right 3 :: Either String Int
--   
--   >>> either length (*2) s
--   3
--   
--   >>> either length (*2) n
--   6
--

either :: (a -> c) -> (b -> c) -> Either a b -> c -- | readParen True p parses what p parses, -- but surrounded with parentheses. -- -- readParen False p parses what p -- parses, but optionally surrounded with parentheses. readParen :: Bool -> ReadS a -> ReadS a -- | The lex function reads a single lexeme from the input, -- discarding initial white space, and returning the characters that -- constitute the lexeme. If the input string contains only white space, -- lex returns a single successful `lexeme' consisting of the -- empty string. (Thus lex "" = [("","")].) If there is -- no legal lexeme at the beginning of the input string, lex fails -- (i.e. returns []). -- -- This lexer is not completely faithful to the Haskell lexical syntax in -- the following respects: -- --

Qualified names are not handled properly
Octal and hexadecimal numerics are not recognized as a single -- token
Comments are not treated properly

lex :: ReadS String -- | A parser for a type a, represented as a function that takes a -- String and returns a list of possible parses as -- (a,String) pairs. -- -- Note that this kind of backtracking parser is very inefficient; -- reading a large structure may be quite slow (cf ReadP). type ReadS a = String -> [(a, String)] odd :: Integral a => a -> Bool -- | lcm x y is the smallest positive integer that both -- x and y divide. lcm :: Integral a => a -> a -> a -- | gcd x y is the non-negative factor of both x -- and y of which every common factor of x and -- y is also a factor; for example gcd 4 2 = 2, -- gcd (-4) 6 = 2, gcd 0 4 = 4. -- gcd 0 0 = 0. (That is, the common divisor -- that is "greatest" in the divisibility preordering.) -- -- Note: Since for signed fixed-width integer types, abs -- minBound < 0, the result may be negative if one of the -- arguments is minBound (and necessarily is if the other -- is 0 or minBound) for such types. gcd :: Integral a => a -> a -> a even :: Integral a => a -> Bool -- | raise a number to an integral power (^^) :: (Fractional a, Integral b) => a -> b -> a infixr 8 ^^ -- | raise a number to a non-negative integral power (^) :: (Num a, Integral b) => a -> b -> a infixr 8 ^ -- | equivalent to showsPrec with a precedence of 0. shows :: Show a => a -> ShowS -- | utility function converting a String to a show function that -- simply prepends the string unchanged. showString :: String -> ShowS -- | utility function that surrounds the inner show function with -- parentheses when the Bool parameter is True. showParen :: Bool -> ShowS -> ShowS -- | utility function converting a Char to a show function that -- simply prepends the character unchanged. showChar :: Char -> ShowS -- | The zipWith3 function takes a function which combines three -- elements, as well as three lists and returns a list of the function -- applied to corresponding elements, analogous to zipWith. It is -- capable of list fusion, but it is restricted to its first list -- argument and its resulting list. -- --

--   zipWith3 (,,) xs ys zs == zip3 xs ys zs
--   zipWith3 f [x1,x2,x3..] [y1,y2,y3..] [z1,z2,z3..] == [f x1 y1 z1, f x2 y2 z2, f x3 y3 z3..]
--

zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] -- | <math>. zipWith generalises zip by zipping with -- the function given as the first argument, instead of a tupling -- function. -- --

--   zipWith (,) xs ys == zip xs ys
--   zipWith f [x1,x2,x3..] [y1,y2,y3..] == [f x1 y1, f x2 y2, f x3 y3..]
--

-- -- For example, zipWith (+) is applied to two lists to -- produce the list of corresponding sums: -- --

--   >>> zipWith (+) [1, 2, 3] [4, 5, 6]
--   [5,7,9]
--

-- -- zipWith is right-lazy: -- --

--   >>> let f = undefined
--   
--   >>> zipWith f [] undefined
--   []
--

-- -- zipWith is capable of list fusion, but it is restricted to its -- first list argument and its resulting list. zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] -- | zip3 takes three lists and returns a list of triples, analogous -- to zip. It is capable of list fusion, but it is restricted to -- its first list argument and its resulting list. zip3 :: [a] -> [b] -> [c] -> [(a, b, c)] -- | The unzip3 function takes a list of triples and returns three -- lists, analogous to unzip. -- --

--   >>> unzip3 []
--   ([],[],[])
--   
--   >>> unzip3 [(1, 'a', True), (2, 'b', False)]
--   ([1,2],"ab",[True,False])
--

unzip3 :: [(a, b, c)] -> ([a], [b], [c]) -- | unzip transforms a list of pairs into a list of first -- components and a list of second components. -- --

--   >>> unzip []
--   ([],[])
--   
--   >>> unzip [(1, 'a'), (2, 'b')]
--   ([1,2],"ab")
--

unzip :: [(a, b)] -> ([a], [b]) -- | takeWhile, applied to a predicate p and a list -- xs, returns the longest prefix (possibly empty) of -- xs of elements that satisfy p. -- --

--   >>> takeWhile (< 3) [1,2,3,4,1,2,3,4]
--   [1,2]
--   
--   >>> takeWhile (< 9) [1,2,3]
--   [1,2,3]
--   
--   >>> takeWhile (< 0) [1,2,3]
--   []
--

takeWhile :: (a -> Bool) -> [a] -> [a] -- | take n, applied to a list xs, returns the -- prefix of xs of length n, or xs itself if -- n >= length xs. -- --

--   >>> take 5 "Hello World!"
--   "Hello"
--   
--   >>> take 3 [1,2,3,4,5]
--   [1,2,3]
--   
--   >>> take 3 [1,2]
--   [1,2]
--   
--   >>> take 3 []
--   []
--   
--   >>> take (-1) [1,2]
--   []
--   
--   >>> take 0 [1,2]
--   []
--

-- -- It is an instance of the more general genericTake, in which -- n may be of any integral type. take :: Int -> [a] -> [a] -- | <math>. Extract the elements after the head of a list, which -- must be non-empty. -- --

--   >>> tail [1, 2, 3]
--   [2,3]
--   
--   >>> tail [1]
--   []
--   
--   >>> tail []
--   *** Exception: Prelude.tail: empty list
--

tail :: [a] -> [a] -- | splitAt n xs returns a tuple where first element is -- xs prefix of length n and second element is the -- remainder of the list: -- --

--   >>> splitAt 6 "Hello World!"
--   ("Hello ","World!")
--   
--   >>> splitAt 3 [1,2,3,4,5]
--   ([1,2,3],[4,5])
--   
--   >>> splitAt 1 [1,2,3]
--   ([1],[2,3])
--   
--   >>> splitAt 3 [1,2,3]
--   ([1,2,3],[])
--   
--   >>> splitAt 4 [1,2,3]
--   ([1,2,3],[])
--   
--   >>> splitAt 0 [1,2,3]
--   ([],[1,2,3])
--   
--   >>> splitAt (-1) [1,2,3]
--   ([],[1,2,3])
--

-- -- It is equivalent to (take n xs, drop n xs) when -- n is not _|_ (splitAt _|_ xs = _|_). -- splitAt is an instance of the more general -- genericSplitAt, in which n may be of any integral -- type. splitAt :: Int -> [a] -> ([a], [a]) -- | span, applied to a predicate p and a list xs, -- returns a tuple where first element is longest prefix (possibly empty) -- of xs of elements that satisfy p and second element -- is the remainder of the list: -- --

--   >>> span (< 3) [1,2,3,4,1,2,3,4]
--   ([1,2],[3,4,1,2,3,4])
--   
--   >>> span (< 9) [1,2,3]
--   ([1,2,3],[])
--   
--   >>> span (< 0) [1,2,3]
--   ([],[1,2,3])
--

-- -- span p xs is equivalent to (takeWhile p xs, -- dropWhile p xs) span :: (a -> Bool) -> [a] -> ([a], [a]) -- | <math>. scanr1 is a variant of scanr that has no -- starting value argument. -- --

--   >>> scanr1 (+) [1..4]
--   [10,9,7,4]
--   
--   >>> scanr1 (+) []
--   []
--   
--   >>> scanr1 (-) [1..4]
--   [-2,3,-1,4]
--   
--   >>> scanr1 (&&) [True, False, True, True]
--   [False,False,True,True]
--   
--   >>> scanr1 (||) [True, True, False, False]
--   [True,True,False,False]
--   
--   >>> force $ scanr1 (+) [1..]
--   *** Exception: stack overflow
--

scanr1 :: (a -> a -> a) -> [a] -> [a] -- | <math>. scanr is the right-to-left dual of scanl. -- Note that the order of parameters on the accumulating function are -- reversed compared to scanl. Also note that -- --

--   head (scanr f z xs) == foldr f z xs.
--

-- --

--   >>> scanr (+) 0 [1..4]
--   [10,9,7,4,0]
--   
--   >>> scanr (+) 42 []
--   [42]
--   
--   >>> scanr (-) 100 [1..4]
--   [98,-97,99,-96,100]
--   
--   >>> scanr (\nextChar reversedString -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
--   ["abcdfoo","bcdfoo","cdfoo","dfoo","foo"]
--   
--   >>> force $ scanr (+) 0 [1..]
--   *** Exception: stack overflow
--

scanr :: (a -> b -> b) -> b -> [a] -> [b] -- | <math>. scanl1 is a variant of scanl that has no -- starting value argument: -- --

--   scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
--

-- --

--   >>> scanl1 (+) [1..4]
--   [1,3,6,10]
--   
--   >>> scanl1 (+) []
--   []
--   
--   >>> scanl1 (-) [1..4]
--   [1,-1,-4,-8]
--   
--   >>> scanl1 (&&) [True, False, True, True]
--   [True,False,False,False]
--   
--   >>> scanl1 (||) [False, False, True, True]
--   [False,False,True,True]
--   
--   >>> scanl1 (+) [1..]
--   * Hangs forever *
--

scanl1 :: (a -> a -> a) -> [a] -> [a] -- | <math>. scanl is similar to foldl, but returns a -- list of successive reduced values from the left: -- --

--   scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]
--

-- -- Note that -- --

--   last (scanl f z xs) == foldl f z xs
--

-- --

--   >>> scanl (+) 0 [1..4]
--   [0,1,3,6,10]
--   
--   >>> scanl (+) 42 []
--   [42]
--   
--   >>> scanl (-) 100 [1..4]
--   [100,99,97,94,90]
--   
--   >>> scanl (\reversedString nextChar -> nextChar : reversedString) "foo" ['a', 'b', 'c', 'd']
--   ["foo","afoo","bafoo","cbafoo","dcbafoo"]
--   
--   >>> scanl (+) 0 [1..]
--   * Hangs forever *
--

scanl :: (b -> a -> b) -> b -> [a] -> [b] -- | reverse xs returns the elements of xs in -- reverse order. xs must be finite. -- --

--   >>> reverse []
--   []
--   
--   >>> reverse [42]
--   [42]
--   
--   >>> reverse [2,5,7]
--   [7,5,2]
--   
--   >>> reverse [1..]
--   * Hangs forever *
--

reverse :: [a] -> [a] -- | replicate n x is a list of length n with -- x the value of every element. It is an instance of the more -- general genericReplicate, in which n may be of any -- integral type. -- --

--   >>> replicate 0 True
--   []
--   
--   >>> replicate (-1) True
--   []
--   
--   >>> replicate 4 True
--   [True,True,True,True]
--

replicate :: Int -> a -> [a] -- | repeat x is an infinite list, with x the -- value of every element. -- --

--   >>> take 20 $ repeat 17
--   [17,17,17,17,17,17,17,17,17...
--

repeat :: a -> [a] -- | <math>. lookup key assocs looks up a key in an -- association list. -- --

--   >>> lookup 2 []
--   Nothing
--   
--   >>> lookup 2 [(1, "first")]
--   Nothing
--   
--   >>> lookup 2 [(1, "first"), (2, "second"), (3, "third")]
--   Just "second"
--

lookup :: Eq a => a -> [(a, b)] -> Maybe b -- | <math>. Extract the last element of a list, which must be finite -- and non-empty. -- --

--   >>> last [1, 2, 3]
--   3
--   
--   >>> last [1..]
--   * Hangs forever *
--   
--   >>> last []
--   *** Exception: Prelude.last: empty list
--

last :: [a] -> a -- | iterate f x returns an infinite list of repeated -- applications of f to x: -- --

--   iterate f x == [x, f x, f (f x), ...]
--

-- -- Note that iterate is lazy, potentially leading to thunk -- build-up if the consumer doesn't force each iterate. See -- iterate' for a strict variant of this function. -- --

--   >>> take 10 $ iterate not True
--   [True,False,True,False...
--   
--   >>> take 10 $ iterate (+3) 42
--   [42,45,48,51,54,57,60,63...
--

iterate :: (a -> a) -> a -> [a] -- | <math>. Return all the elements of a list except the last one. -- The list must be non-empty. -- --

--   >>> init [1, 2, 3]
--   [1,2]
--   
--   >>> init [1]
--   []
--   
--   >>> init []
--   *** Exception: Prelude.init: empty list
--

init :: [a] -> [a] -- | <math>. Extract the first element of a list, which must be -- non-empty. -- --

--   >>> head [1, 2, 3]
--   1
--   
--   >>> head [1..]
--   1
--   
--   >>> head []
--   *** Exception: Prelude.head: empty list
--

head :: [a] -> a -- | dropWhile p xs returns the suffix remaining after -- takeWhile p xs. -- --

--   >>> dropWhile (< 3) [1,2,3,4,5,1,2,3]
--   [3,4,5,1,2,3]
--   
--   >>> dropWhile (< 9) [1,2,3]
--   []
--   
--   >>> dropWhile (< 0) [1,2,3]
--   [1,2,3]
--

dropWhile :: (a -> Bool) -> [a] -> [a] -- | drop n xs returns the suffix of xs after the -- first n elements, or [] if n >= length -- xs. -- --

--   >>> drop 6 "Hello World!"
--   "World!"
--   
--   >>> drop 3 [1,2,3,4,5]
--   [4,5]
--   
--   >>> drop 3 [1,2]
--   []
--   
--   >>> drop 3 []
--   []
--   
--   >>> drop (-1) [1,2]
--   [1,2]
--   
--   >>> drop 0 [1,2]
--   [1,2]
--

-- -- It is an instance of the more general genericDrop, in which -- n may be of any integral type. drop :: Int -> [a] -> [a] -- | cycle ties a finite list into a circular one, or equivalently, -- the infinite repetition of the original list. It is the identity on -- infinite lists. -- --

--   >>> cycle []
--   *** Exception: Prelude.cycle: empty list
--   
--   >>> take 20 $ cycle [42]
--   [42,42,42,42,42,42,42,42,42,42...
--   
--   >>> take 20 $ cycle [2, 5, 7]
--   [2,5,7,2,5,7,2,5,7,2,5,7...
--

cycle :: [a] -> [a] -- | break, applied to a predicate p and a list -- xs, returns a tuple where first element is longest prefix -- (possibly empty) of xs of elements that do not satisfy -- p and second element is the remainder of the list: -- --

--   >>> break (> 3) [1,2,3,4,1,2,3,4]
--   ([1,2,3],[4,1,2,3,4])
--   
--   >>> break (< 9) [1,2,3]
--   ([],[1,2,3])
--   
--   >>> break (> 9) [1,2,3]
--   ([1,2,3],[])
--

-- -- break p is equivalent to span (not . -- p). break :: (a -> Bool) -> [a] -> ([a], [a]) -- | List index (subscript) operator, starting from 0. It is an instance of -- the more general genericIndex, which takes an index of any -- integral type. -- --

--   >>> ['a', 'b', 'c'] !! 0
--   'a'
--   
--   >>> ['a', 'b', 'c'] !! 2
--   'c'
--   
--   >>> ['a', 'b', 'c'] !! 3
--   *** Exception: Prelude.!!: index too large
--   
--   >>> ['a', 'b', 'c'] !! (-1)
--   *** Exception: Prelude.!!: negative index
--

(!!) :: [a] -> Int -> a infixl 9 !! -- | The maybe function takes a default value, a function, and a -- Maybe value. If the Maybe value is Nothing, the -- function returns the default value. Otherwise, it applies the function -- to the value inside the Just and returns the result. -- --

Examples

-- -- Basic usage: -- --

--   >>> maybe False odd (Just 3)
--   True
--

-- --

--   >>> maybe False odd Nothing
--   False
--

-- -- Read an integer from a string using readMaybe. If we succeed, -- return twice the integer; that is, apply (*2) to it. If -- instead we fail to parse an integer, return 0 by default: -- --

--   >>> import Text.Read ( readMaybe )
--   
--   >>> maybe 0 (*2) (readMaybe "5")
--   10
--   
--   >>> maybe 0 (*2) (readMaybe "")
--   0
--

-- -- Apply show to a Maybe Int. If we have Just n, -- we want to show the underlying Int n. But if we have -- Nothing, we return the empty string instead of (for example) -- "Nothing": -- --

--   >>> maybe "" show (Just 5)
--   "5"
--   
--   >>> maybe "" show Nothing
--   ""
--

maybe :: b -> (a -> b) -> Maybe a -> b -- | uncurry converts a curried function to a function on pairs. -- --

Examples

-- --

--   >>> uncurry (+) (1,2)
--   3
--

-- --

--   >>> uncurry ($) (show, 1)
--   "1"
--

-- --

--   >>> map (uncurry max) [(1,2), (3,4), (6,8)]
--   [2,4,8]
--

uncurry :: (a -> b -> c) -> (a, b) -> c -- | curry converts an uncurried function to a curried function. -- --

Examples

-- --

--   >>> curry fst 1 2
--   1
--

curry :: ((a, b) -> c) -> a -> b -> c -- | the same as flip (-). -- -- Because - is treated specially in the Haskell grammar, -- (- e) is not a section, but an application of -- prefix negation. However, (subtract -- exp) is equivalent to the disallowed section. subtract :: Num a => a -> a -> a -- | until p f yields the result of applying f -- until p holds. until :: (a -> Bool) -> (a -> a) -> a -> a -- | flip f takes its (first) two arguments in the reverse -- order of f. -- --

--   >>> flip (++) "hello" "world"
--   "worldhello"
--

flip :: (a -> b -> c) -> b -> a -> c -- | asTypeOf is a type-restricted version of const. It is -- usually used as an infix operator, and its typing forces its first -- argument (which is usually overloaded) to have the same type as the -- second. asTypeOf :: a -> a -> a -- | Same as >>=, but with the arguments interchanged. (=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 =<< -- | Strict (call-by-value) application operator. It takes a function and -- an argument, evaluates the argument to weak head normal form (WHNF), -- then calls the function with that value. ($!) :: forall (r :: RuntimeRep) a (b :: TYPE r). (a -> b) -> a -> b infixr 0 $! -- | A special case of error. It is expected that compilers will -- recognize this and insert error messages which are more appropriate to -- the context in which undefined appears. undefined :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => a -- | A variant of error that does not produce a stack trace. errorWithoutStackTrace :: forall (r :: RuntimeRep) (a :: TYPE r). [Char] -> a -- | error stops execution and displays an error message. error :: forall (r :: RuntimeRep) (a :: TYPE r). HasCallStack => [Char] -> a -- | Boolean "and", lazy in the second argument (&&) :: Bool -> Bool -> Bool infixr 3 && -- | Boolean "not" not :: Bool -> Bool -- | Boolean "or", lazy in the second argument (||) :: Bool -> Bool -> Bool infixr 2 || -- | Conditional failure of Alternative computations. Defined by -- --

--   guard True  = pure ()
--   guard False = empty
--

-- --

Examples

-- -- Common uses of guard include conditionally signaling an error -- in an error monad and conditionally rejecting the current choice in an -- Alternative-based parser. -- -- As an example of signaling an error in the error monad Maybe, -- consider a safe division function safeDiv x y that returns -- Nothing when the denominator y is zero and -- Just (x `div` y) otherwise. For example: -- --

--   >>> safeDiv 4 0
--   Nothing
--

-- --

--   >>> safeDiv 4 2
--   Just 2
--

-- -- A definition of safeDiv using guards, but not guard: -- --

--   safeDiv :: Int -> Int -> Maybe Int
--   safeDiv x y | y /= 0    = Just (x `div` y)
--               | otherwise = Nothing
--

-- -- A definition of safeDiv using guard and Monad -- do-notation: -- --

--   safeDiv :: Int -> Int -> Maybe Int
--   safeDiv x y = do
--     guard (y /= 0)
--     return (x `div` y)
--

guard :: Alternative f => Bool -> f () -- | The join function is the conventional monad join operator. It -- is used to remove one level of monadic structure, projecting its bound -- argument into the outer level. -- -- 'join bss' can be understood as the do -- expression -- --

--   do bs <- bss
--      bs
--

-- --

Examples

-- -- A common use of join is to run an IO computation -- returned from an STM transaction, since STM transactions -- can't perform IO directly. Recall that -- --

--   atomically :: STM a -> IO a
--

-- -- is used to run STM transactions atomically. So, by specializing -- the types of atomically and join to -- --

--   atomically :: STM (IO b) -> IO (IO b)
--   join       :: IO (IO b)  -> IO b
--

-- -- we can compose them as -- --

--   join . atomically :: STM (IO b) -> IO b
--

-- -- to run an STM transaction and the IO action it returns. join :: Monad m => m (m a) -> m a -- | The Monad class defines the basic operations over a -- monad, a concept from a branch of mathematics known as -- category theory. From the perspective of a Haskell programmer, -- however, it is best to think of a monad as an abstract datatype -- of actions. Haskell's do expressions provide a convenient -- syntax for writing monadic expressions. -- -- Instances of Monad should satisfy the following: -- --

Left identity return a >>= k = k -- a
Right identity m >>= return = -- m
Associativity m >>= (\x -> k x -- >>= h) = (m >>= k) >>= -- h

-- -- Furthermore, the Monad and Applicative operations should -- relate as follows: -- --

```
pure = return
```

m1 <*> m2 = m1 >>= (x1 -> m2
--   >>= (x2 -> return (x1 x2)))

-- -- The above laws imply: -- --

```
fmap f xs = xs >>= return .
--   f
```
```
(>>) = (*>)
```

--   do a <- as
--      bs a
--

--   do as
--      bs
--

Identity fmap id == id
Composition fmap (f . g) == fmap f . -- fmap g

Examples

-- -- Convert from a Maybe Int to a Maybe String -- using show: -- --

--   >>> fmap show Nothing
--   Nothing
--   
--   >>> fmap show (Just 3)
--   Just "3"
--

-- -- Convert from an Either Int Int to an Either Int -- String using show: -- --

--   >>> fmap show (Left 17)
--   Left 17
--   
--   >>> fmap show (Right 17)
--   Right "17"
--

-- -- Double each element of a list: -- --

--   >>> fmap (*2) [1,2,3]
--   [2,4,6]
--

-- -- Apply even to the second element of a pair: -- --

--   >>> fmap even (2,2)
--   (2,True)
--

--   >>> fmap even ("hello", 1.0, 4)
--   ("hello",1.0,True)
--

fmap :: Functor f => (a -> b) -> f a -> f b -- | Replace all locations in the input with the same value. The default -- definition is fmap . const, but this may be -- overridden with a more efficient version. (<$) :: Functor f => a -> f b -> f a infixl 4 <$ -- | When a value is bound in do-notation, the pattern on the left -- hand side of <- might not match. In this case, this class -- provides a function to recover. -- -- A Monad without a MonadFail instance may only be used in -- conjunction with pattern that always match, such as newtypes, tuples, -- data types with only a single data constructor, and irrefutable -- patterns (~pat). -- -- Instances of MonadFail should satisfy the following law: -- fail s should be a left zero for >>=, -- --

--   fail s >>= f  =  fail s
--

-- -- If your Monad is also MonadPlus, a popular definition is -- --

--   fail _ = mzero
--

class Monad m => MonadFail (m :: Type -> Type) -- | Map each element of a structure to a monadic action, evaluate these -- actions from left to right, and collect the results. For a version -- that ignores the results see mapM_. -- --

Examples

-- -- Basic usage: -- -- The first two examples are instances where the input and and output of -- sequence are isomorphic. -- --

--   >>> sequence $ Right [1,2,3,4]
--   [Right 1,Right 2,Right 3,Right 4]
--

-- --

--   >>> sequence $ [Right 1,Right 2,Right 3,Right 4]
--   Right [1,2,3,4]
--

-- -- The following examples demonstrate short circuit behavior for -- sequence. -- --

--   >>> sequence $ Left [1,2,3,4]
--   Left [1,2,3,4]
--

-- --

--   >>> sequence $ [Left 0, Right 1,Right 2,Right 3,Right 4]
--   Left 0
--

sequence :: (Traversable t, Monad m) => t (m a) -> m (t a) -- | forM_ is mapM_ with its arguments flipped. For a version -- that doesn't ignore the results see forM. -- -- forM_ is just like for_, but specialised to monadic -- actions. forM_ :: (Foldable t, Monad m) => t a -> (a -> m b) -> m () -- | Map each element of a structure to a monadic action, evaluate these -- actions from left to right, and ignore the results. For a version that -- doesn't ignore the results see mapM. -- -- mapM_ is just like traverse_, but specialised to monadic -- actions. mapM_ :: (Foldable t, Monad m) => (a -> m b) -> t a -> m () -- | Monads that also support choice and failure. class (Alternative m, Monad m) => MonadPlus (m :: Type -> Type) -- | The identity of mplus. It should also satisfy the equations -- --

--   mzero >>= f  =  mzero
--   v >> mzero   =  mzero
--

-- -- The default definition is -- --

--   mzero = empty
--

mzero :: MonadPlus m => m a -- | An associative operation. The default definition is -- --

--   mplus = (<|>)
--

mplus :: MonadPlus m => m a -> m a -> m a -- | zipWithM_ is the extension of zipWithM which ignores the -- final result. zipWithM_ :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m () -- | The zipWithM function generalizes zipWith to arbitrary -- applicative functors. zipWithM :: Applicative m => (a -> b -> m c) -> [a] -> [b] -> m [c] -- | The reverse of when. unless :: Applicative f => Bool -> f () -> f () -- | Like replicateM, but discards the result. -- --

Examples

-- --

--   >>> replicateM_ 3 (putStrLn "a")
--   a
--   a
--   a
--

replicateM_ :: Applicative m => Int -> m a -> m () -- | replicateM n act performs the action act -- n times, and then returns the list of results: -- --

Examples

-- --

--   >>> import Control.Monad.State
--   
--   >>> runState (replicateM 3 $ state $ \s -> (s, s + 1)) 1
--   ([1,2,3],4)
--

replicateM :: Applicative m => Int -> m a -> m [a] -- | Direct MonadPlus equivalent of filter. -- --

Examples

-- -- The filter function is just mfilter specialized to the -- list monad: -- --

--   filter = ( mfilter :: (a -> Bool) -> [a] -> [a] )
--

-- -- An example using mfilter with the Maybe monad: -- --

--   >>> mfilter odd (Just 1)
--   Just 1
--   
--   >>> mfilter odd (Just 2)
--   Nothing
--

mfilter :: MonadPlus m => (a -> Bool) -> m a -> m a -- | The mapAndUnzipM function maps its first argument over a list, -- returning the result as a pair of lists. This function is mainly used -- with complicated data structures or a state monad. mapAndUnzipM :: Applicative m => (a -> m (b, c)) -> [a] -> m ([b], [c]) -- | Repeat an action indefinitely. -- --

Examples

-- -- A common use of forever is to process input from network -- sockets, Handles, and channels (e.g. MVar and -- Chan). -- -- For example, here is how we might implement an echo server, -- using forever both to listen for client connections on a -- network socket and to echo client input on client connection handles: -- --

--   echoServer :: Socket -> IO ()
--   echoServer socket = forever $ do
--     client <- accept socket
--     forkFinally (echo client) (\_ -> hClose client)
--     where
--       echo :: Handle -> IO ()
--       echo client = forever $
--         hGetLine client >>= hPutStrLn client
--

-- -- Note that "forever" isn't necessarily non-terminating. If the action -- is in a MonadPlus and short-circuits after some number -- of iterations. then forever actually returns -- mzero, effectively short-circuiting its caller. forever :: Applicative f => f a -> f b -- | Like foldM, but discards the result. foldM_ :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m () -- | The foldM function is analogous to foldl, except that -- its result is encapsulated in a monad. Note that foldM works -- from left-to-right over the list arguments. This could be an issue -- where (>>) and the `folded function' are not -- commutative. -- --

--   foldM f a1 [x1, x2, ..., xm]
--   
--   ==
--   
--   do
--     a2 <- f a1 x1
--     a3 <- f a2 x2
--     ...
--     f am xm
--

-- -- If right-to-left evaluation is required, the input list should be -- reversed. -- -- Note: foldM is the same as foldlM foldM :: (Foldable t, Monad m) => (b -> a -> m b) -> b -> t a -> m b -- | This generalizes the list-based filter function. filterM :: Applicative m => (a -> m Bool) -> [a] -> m [a] -- | Left-to-right composition of Kleisli arrows. -- -- '(bs >=> cs) a' can be understood as the -- do expression -- --

--   do b <- bs a
--      cs b
--

(>=>) :: Monad m => (a -> m b) -> (b -> m c) -> a -> m c infixr 1 >=> -- | Right-to-left composition of Kleisli arrows. -- (>=>), with the arguments flipped. -- -- Note how this operator resembles function composition -- (.): -- --

--   (.)   ::            (b ->   c) -> (a ->   b) -> a ->   c
--   (<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c
--

(<=<) :: Monad m => (b -> m c) -> (a -> m b) -> a -> m c infixr 1 <=< -- | Strict version of <$>. (<$!>) :: Monad m => (a -> b) -> m a -> m b infixl 4 <$!> -- | forM is mapM with its arguments flipped. For a version -- that ignores the results see forM_. forM :: (Traversable t, Monad m) => t a -> (a -> m b) -> m (t b) -- | Evaluate each monadic action in the structure from left to right, and -- ignore the results. For a version that doesn't ignore the results see -- sequence. -- -- sequence_ is just like sequenceA_, but specialised to -- monadic actions. sequence_ :: (Foldable t, Monad m) => t (m a) -> m () -- | The sum of a collection of actions, generalizing concat. -- -- msum is just like asum, but specialised to -- MonadPlus. msum :: (Foldable t, MonadPlus m) => t (m a) -> m a -- | void value discards or ignores the result of -- evaluation, such as the return value of an IO action. -- --

Examples

-- -- Replace the contents of a Maybe Int with unit: -- --

--   >>> void Nothing
--   Nothing
--   
--   >>> void (Just 3)
--   Just ()
--

-- -- Replace the contents of an Either Int -- Int with unit, resulting in an Either -- Int (): -- --

--   >>> void (Left 8675309)
--   Left 8675309
--   
--   >>> void (Right 8675309)
--   Right ()
--

-- -- Replace every element of a list with unit: -- --

--   >>> void [1,2,3]
--   [(),(),()]
--

-- -- Replace the second element of a pair with unit: -- --

--   >>> void (1,2)
--   (1,())
--

-- -- Discard the result of an IO action: -- --

--   >>> mapM print [1,2]
--   1
--   2
--   [(),()]
--   
--   >>> void $ mapM print [1,2]
--   1
--   2
--

void :: Functor f => f a -> f () -- | Conditional execution of Applicative expressions. For example, -- --

--   when debug (putStrLn "Debugging")
--

-- -- will output the string Debugging if the Boolean value -- debug is True, and otherwise do nothing. when :: Applicative f => Bool -> f () -> f () -- | Promote a function to a monad, scanning the monadic arguments from -- left to right (cf. liftM2). liftM5 :: Monad m => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r -- | Promote a function to a monad, scanning the monadic arguments from -- left to right (cf. liftM2). liftM4 :: Monad m => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r -- | Promote a function to a monad, scanning the monadic arguments from -- left to right (cf. liftM2). liftM3 :: Monad m => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r -- | Promote a function to a monad, scanning the monadic arguments from -- left to right. For example, -- --

--   liftM2 (+) [0,1] [0,2] = [0,2,1,3]
--   liftM2 (+) (Just 1) Nothing = Nothing
--

liftM2 :: Monad m => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r -- | Promote a function to a monad. liftM :: Monad m => (a1 -> r) -> m a1 -> m r -- | In many situations, the liftM operations can be replaced by -- uses of ap, which promotes function application. -- --

--   return f `ap` x1 `ap` ... `ap` xn
--

-- -- is equivalent to -- --

--   liftMn f x1 x2 ... xn
--

ap :: Monad m => m (a -> b) -> m a -> m b -- | Same as >>=, but with the arguments interchanged. (=<<) :: Monad m => (a -> m b) -> m a -> m b infixr 1 =<< -- | Like findM, but also allows you to compute some additional -- information in the predicate. firstJustM :: Monad m => (a -> m (Maybe b)) -> [a] -> m (Maybe b) -- | Like find, but where the test can be monadic. -- --

--   findM (Just . isUpper) "teST"             == Just (Just 'S')
--   findM (Just . isUpper) "test"             == Just Nothing
--   findM (Just . const True) ["x",undefined] == Just (Just "x")
--

findM :: Monad m => (a -> m Bool) -> [a] -> m (Maybe a) -- | A version of and lifted to a monad. Retains the -- short-circuiting behaviour. -- --

--   andM [Just True,Just False,undefined] == Just False
--   andM [Just True,Just True ,undefined] == undefined
--   \xs -> Just (and xs) == andM (map Just xs)
--

andM :: Monad m => [m Bool] -> m Bool -- | A version of or lifted to a monad. Retains the short-circuiting -- behaviour. -- --

--   orM [Just False,Just True ,undefined] == Just True
--   orM [Just False,Just False,undefined] == undefined
--   \xs -> Just (or xs) == orM (map Just xs)
--

orM :: Monad m => [m Bool] -> m Bool -- | A version of all lifted to a monad. Retains the -- short-circuiting behaviour. -- --

--   allM Just [True,False,undefined] == Just False
--   allM Just [True,True ,undefined] == undefined
--   \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--

allM :: Monad m => (a -> m Bool) -> [a] -> m Bool -- | A version of any lifted to a monad. Retains the -- short-circuiting behaviour. -- --

--   anyM Just [False,True ,undefined] == Just True
--   anyM Just [False,False,undefined] == undefined
--   \(f :: Int -> Maybe Bool) xs -> anyM f xs == orM (map f xs)
--

anyM :: Monad m => (a -> m Bool) -> [a] -> m Bool -- | The lazy && operator lifted to a monad. If the first -- argument evaluates to False the second argument will not be -- evaluated. -- --

--   Just False &&^ undefined  == Just False
--   Just True  &&^ Just True  == Just True
--   Just True  &&^ Just False == Just False
--

(&&^) :: Monad m => m Bool -> m Bool -> m Bool -- | The lazy || operator lifted to a monad. If the first argument -- evaluates to True the second argument will not be evaluated. -- --

--   Just True  ||^ undefined  == Just True
--   Just False ||^ Just True  == Just True
--   Just False ||^ Just False == Just False
--

(||^) :: Monad m => m Bool -> m Bool -> m Bool -- | Like not, but where the test can be monadic. notM :: Functor m => m Bool -> m Bool -- | Like if, but where the test can be monadic. ifM :: Monad m => m Bool -> m a -> m a -> m a -- | Like unless, but where the test can be monadic. unlessM :: Monad m => m Bool -> m () -> m () -- | Like when, but where the test can be monadic. whenM :: Monad m => m Bool -> m () -> m () -- | Keep running an operation until it becomes a Just, then return -- the value inside the Just as the result of the overall loop. untilJustM :: Monad m => m (Maybe a) -> m a -- | Keep running an operation until it becomes a Nothing, -- accumulating the monoid results inside the Justs as the result -- of the overall loop. whileJustM :: (Monad m, Monoid a) => m (Maybe a) -> m a -- | Keep running an operation until it becomes False. As an -- example: -- --

--   whileM $ do sleep 0.1; notM $ doesFileExist "foo.txt"
--   readFile "foo.txt"
--

-- -- If you need some state persisted between each test, use loopM. whileM :: Monad m => m Bool -> m () -- | A monadic version of loop, where the predicate returns -- Left as a seed for the next loop or Right to abort the -- loop. loopM :: Monad m => (a -> m (Either a b)) -> a -> m b -- | A looping operation, where the predicate returns Left as a seed -- for the next loop or Right to abort the loop. -- --

--   loop (\x -> if x < 10 then Left $ x * 2 else Right $ show x) 1 == "16"
--

loop :: (a -> Either a b) -> a -> b -- | A version of mapMaybe that works with a monadic predicate. mapMaybeM :: Monad m => (a -> m (Maybe b)) -> [a] -> m [b] -- | A version of mconcatMap that works with a monadic predicate. mconcatMapM :: (Monad m, Monoid b) => (a -> m b) -> [a] -> m b -- | Like concatMapM, but has its arguments flipped, so can be used -- instead of the common fmap concat $ forM pattern. concatForM :: Monad m => [a] -> (a -> m [b]) -> m [b] -- | A version of concatMap that works with a monadic predicate. concatMapM :: Monad m => (a -> m [b]) -> [a] -> m [b] -- | A version of partition that works with a monadic predicate. -- --

--   partitionM (Just . even) [1,2,3] == Just ([2], [1,3])
--   partitionM (const Nothing) [1,2,3] == Nothing
--

partitionM :: Monad m => (a -> m Bool) -> [a] -> m ([a], [a]) -- | Like fold1M but discards the result. fold1M_ :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m () -- | A variant of foldM that has no base case, and thus may only be -- applied to non-empty lists. -- --

--   fold1M (\x y -> Just x) [] == undefined
--   fold1M (\x y -> Just $ x + y) [1, 2, 3] == Just 6
--

fold1M :: (Partial, Monad m) => (a -> a -> m a) -> [a] -> m a -- | Monadic generalisation of either. eitherM :: Monad m => (a -> m c) -> (b -> m c) -> m (Either a b) -> m c -- | Monadic generalisation of fromMaybe. fromMaybeM :: Monad m => m a -> m (Maybe a) -> m a -- | Monadic generalisation of maybe. maybeM :: Monad m => m b -> (a -> m b) -> m (Maybe a) -> m b -- | The identity function which requires the inner argument to be -- (). Useful for functions with overloaded return types. -- --

--   \(x :: Maybe ()) -> unit x == x
--

unit :: m () -> m () -- | Like whenMaybe, but where the test can be monadic. whenMaybeM :: Monad m => m Bool -> m a -> m (Maybe a) -- | Like when, but return either Nothing if the predicate -- was False, of Just with the result of the computation. -- --

--   whenMaybe True  (print 1) == fmap Just (print 1)
--   whenMaybe False (print 1) == pure Nothing
--

whenMaybe :: Applicative m => Bool -> m a -> m (Maybe a) -- | Return either a pure value if a condition is True, -- otherwise empty. -- --

--   pureIf @Maybe True  5 == Just 5
--   pureIf @Maybe False 5 == Nothing
--   pureIf @[]    True  5 == [5]
--   pureIf @[]    False 5 == []
--

pureIf :: Alternative m => Bool -> a -> m a -- | Like whenJust, but where the test can be monadic. whenJustM :: Monad m => m (Maybe a) -> (a -> m ()) -> m () -- | Perform some operation on Just, given the field inside the -- Just. This is a specialized for_. -- --

--   whenJust Nothing  print == pure ()
--   whenJust (Just 1) print == print 1
--

whenJust :: Applicative m => Maybe a -> (a -> m ()) -> m () -- | Monads in which IO computations may be embedded. Any monad -- built by applying a sequence of monad transformers to the IO -- monad will be an instance of this class. -- -- Instances should satisfy the following laws, which state that -- liftIO is a transformer of monads: -- --

```
liftIO . return = return
```

liftIO (m >>= f) = liftIO m >>=
--   (liftIO . f)

class Monad m => MonadIO (m :: Type -> Type) -- | Lift a computation from the IO monad. This allows us to run IO -- computations in any monadic stack, so long as it supports these kinds -- of operations (i.e. IO is the base monad for the stack). -- --

Example

-- --

--   import Control.Monad.Trans.State -- from the "transformers" library
--   
--   printState :: Show s => StateT s IO ()
--   printState = do
--     state <- get
--     liftIO $ print state
--

-- -- Had we omitted liftIO, we would have ended up with -- this error: -- --

--   • Couldn't match type ‘IO’ with ‘StateT s IO’
--    Expected type: StateT s IO ()
--      Actual type: IO ()
--

-- -- The important part here is the mismatch between StateT s IO -- () and IO (). -- -- Luckily, we know of a function that takes an IO a and -- returns an (m a): liftIO, enabling us to run -- the program and see the expected results: -- --

--   > evalStateT printState "hello"
--   "hello"
--   
--   > evalStateT printState 3
--   3
--

liftIO :: MonadIO m => IO a -> m a -- | The class of monoids (types with an associative binary operation that -- has an identity). Instances should satisfy the following: -- --

Right identity x <> mempty = -- x
Left identity mempty <> x = -- x
Associativity x <> (y <> z) = -- (x <> y) <> z (Semigroup -- law)
Concatenation mconcat = foldr -- (<>) mempty

--   >>> "Hello world" <> mempty
--   "Hello world"
--

--   >>> mconcat ["Hello", " ", "Haskell", "!"]
--   "Hello Haskell!"
--

mconcat :: Monoid a => [a] -> a -- | The class of semigroups (types with an associative binary operation). -- -- Instances should satisfy the following: -- --

Associativity x <> (y <> z) = -- (x <> y) <> z

class Semigroup a -- | An associative operation. -- --

--   >>> [1,2,3] <> [4,5,6]
--   [1,2,3,4,5,6]
--

(<>) :: Semigroup a => a -> a -> a -- | Reduce a non-empty list with <> -- -- The default definition should be sufficient, but this can be -- overridden for efficiency. -- --

--   >>> import Data.List.NonEmpty (NonEmpty (..))
--   
--   >>> sconcat $ "Hello" :| [" ", "Haskell", "!"]
--   "Hello Haskell!"
--

sconcat :: Semigroup a => NonEmpty a -> a -- | Repeat a value n times. -- -- Given that this works on a Semigroup it is allowed to fail if -- you request 0 or fewer repetitions, and the default definition will do -- so. -- -- By making this a member of the class, idempotent semigroups and -- monoids can upgrade this to execute in <math> by picking -- stimes = stimesIdempotent or stimes = -- stimesIdempotentMonoid respectively. -- --

--   >>> stimes 4 [1]
--   [1,1,1,1]
--

stimes :: (Semigroup a, Integral b) => b -> a -> a infixr 6 <> -- | 8-bit unsigned integer type data Word8 -- | Representable types of kind *. This class is derivable in GHC -- with the DeriveGeneric flag on. -- -- A Generic instance must satisfy the following laws: -- --

--   from . to ≡ id
--   to . from ≡ id
--

class Generic a -- | Natural number -- -- Invariant: numbers <= 0xffffffffffffffff use the NS -- constructor data Natural -- | A space efficient, packed, unboxed Unicode text type. data Text type LazyText = Text -- | A space-efficient representation of a Word8 vector, supporting -- many efficient operations. -- -- A ByteString contains 8-bit bytes, or by using the operations -- from Data.ByteString.Char8 it can be interpreted as containing -- 8-bit characters. data ByteString type LazyByteString = ByteString packText :: String -> Text unpackText :: Text -> String -- | The most general way to run a parser. runParserT p state filePath -- input runs parser p on the input list of tokens -- input, obtained from source filePath with the -- initial user state st. The filePath is only used in -- error messages and may be the empty string. Returns a computation in -- the underlying monad m that return either a ParseError -- (Left) or a value of type a (Right). runParserT :: Stream s m t => ParsecT s u m a -> u -> SourceName -> s -> m (Either ParseError a) -- | The most general way to run a parser over the Identity monad. -- runParser p state filePath input runs parser p on -- the input list of tokens input, obtained from source -- filePath with the initial user state st. The -- filePath is only used in error messages and may be the empty -- string. Returns either a ParseError (Left) or a value of -- type a (Right). -- --

--   parseFromFile p fname
--     = do{ input <- readFile fname
--         ; return (runParser p () fname input)
--         }
--

runParser :: Stream s Identity t => Parsec s u a -> u -> SourceName -> s -> Either ParseError a -- | Convenience wrapper around runParser that uses the -- HasParser class to determine the desired parser for the given -- result type. The function reports syntax errors by throwing -- ParseError. This approach is inherently impure and complicates -- error handling greatly. Use this function only on occasions where -- parser errors are fatal errors that your code cannot recover from. In -- almost all cases, parseM is the better choice. -- --

--   >>> parse "Natural" "12345" :: Natural
--   12345
--

-- -- Like parseM, this function does not skip over any white space. -- Use Parsec's primitive runParser or runParserT functions -- if you don't like this behavior: -- --

--   >>> runParser (spaces >> parser) () "Natural" "  1  " :: Either ParseError Natural
--   Right 1
--

parse :: (Stream input Identity Char, HasParser a) => ErrorContext -> input -> a -- | Convenience wrapper around runParserT that uses the -- HasParser class to determine the desired parser for the given -- result type. The function reports syntax errors via fail. -- --

--   >>> parseM "Natural" "987654321" :: IO Natural
--   987654321
--   
--   >>> parseM "Natural" "123456789" :: Maybe Natural
--   Just 123456789
--

-- -- Please note that parsers run this way do not ignore any white space: -- --

--   >>> parseM "Natural" " 1" :: Maybe Natural
--   Nothing
--   
--   >>> parseM "Natural" "1 " :: Maybe Natural
--   Nothing
--

parseM :: (MonadFail m, Stream input m Char, HasParser a) => ErrorContext -> input -> m a -- | A simplified ParsecT parser that consumes some kind of -- character stream without requiring any particular state state. type CharParser st input (m :: Type -> Type) a = Stream st m Char => ParsecT st input m a -- | Types that are instances of this class can be parsed and constructed -- from some character based text representation. class HasParser a parser :: forall st input (m :: Type -> Type). HasParser a => CharParser st input m a -- | Parsers functions like parse or parseM use this type to -- provide a helpful context in case the parser failes. Parsec uses the -- synonym SourceName for the same purpose, but in fact this type -- doesn't necessarily have to be a file name. It can be any name or -- identifier. Oftentimes, it it's useful to pass the name of the type -- that the parser attempted to parse. type ErrorContext = String -- | Pretty printing class. The precedence level is used in a similar way -- as in the Show class. Minimal complete definition is either -- pPrintPrec or pPrint. class Pretty a pPrint :: Pretty a => a -> Doc -- | Pretty print a value with the prettyNormal level. prettyShow :: Pretty a => a -> String -- | The abstract type of documents. A Doc represents a set of -- layouts. A Doc with no occurrences of Union or NoDoc represents just -- one layout. data Doc -- | A type that can be converted to JSON. -- -- Instances in general must specify toJSON and -- should (but don't need to) specify toEncoding. -- -- An example type and instance: -- --

--   -- Allow ourselves to write Text literals.
--   {-# LANGUAGE OverloadedStrings #-}
--   
--   data Coord = Coord { x :: Double, y :: Double }
--   
--   instance ToJSON Coord where
--     toJSON (Coord x y) = object ["x" .= x, "y" .= y]
--   
--     toEncoding (Coord x y) = pairs ("x" .= x <> "y" .= y)
--

-- -- Instead of manually writing your ToJSON instance, there are two -- options to do it automatically: -- --

Data.Aeson.TH provides Template Haskell functions which -- will derive an instance at compile time. The generated instance is -- optimized for your type so it will probably be more efficient than the -- following option.
The compiler can provide a default generic implementation for -- toJSON.

-- -- To use the second, simply add a deriving Generic -- clause to your datatype and declare a ToJSON instance. If you -- require nothing other than defaultOptions, it is sufficient to -- write (and this is the only alternative where the default -- toJSON implementation is sufficient): -- --

--   {-# LANGUAGE DeriveGeneric #-}
--   
--   import GHC.Generics
--   
--   data Coord = Coord { x :: Double, y :: Double } deriving Generic
--   
--   instance ToJSON Coord where
--       toEncoding = genericToEncoding defaultOptions
--

-- -- or more conveniently using the DerivingVia extension -- --

--   deriving via Generically Coord instance ToJSON Coord
--

-- -- If on the other hand you wish to customize the generic decoding, you -- have to implement both methods: -- --

--   customOptions = defaultOptions
--                   { fieldLabelModifier = map toUpper
--                   }
--   
--   instance ToJSON Coord where
--       toJSON     = genericToJSON customOptions
--       toEncoding = genericToEncoding customOptions
--

-- -- Previous versions of this library only had the toJSON method. -- Adding toEncoding had two reasons: -- --

toEncoding is more efficient for the common case that the -- output of toJSON is directly serialized to a -- ByteString. Further, expressing either method in terms of the -- other would be non-optimal.
The choice of defaults allows a smooth transition for existing -- users: Existing instances that do not define toEncoding still -- compile and have the correct semantics. This is ensured by making the -- default implementation of toEncoding use toJSON. This -- produces correct results, but since it performs an intermediate -- conversion to a Value, it will be less efficient than directly -- emitting an Encoding. (this also means that specifying nothing -- more than instance ToJSON Coord would be sufficient as a -- generically decoding instance, but there probably exists no good -- reason to not specify toEncoding in new instances.)

class ToJSON a -- | A type that can be converted from JSON, with the possibility of -- failure. -- -- In many cases, you can get the compiler to generate parsing code for -- you (see below). To begin, let's cover writing an instance by hand. -- -- There are various reasons a conversion could fail. For example, an -- Object could be missing a required key, an Array could -- be of the wrong size, or a value could be of an incompatible type. -- -- The basic ways to signal a failed conversion are as follows: -- --

fail yields a custom error message: it is the recommended -- way of reporting a failure;
empty (or mzero) is uninformative: use it when the -- error is meant to be caught by some (<|>);
typeMismatch can be used to report a failure when the -- encountered value is not of the expected JSON type; unexpected -- is an appropriate alternative when more than one type may be expected, -- or to keep the expected type implicit.

-- -- prependFailure (or modifyFailure) add more information -- to a parser's error messages. -- -- An example type and instance using typeMismatch and -- prependFailure: -- --

--   -- Allow ourselves to write Text literals.
--   {-# LANGUAGE OverloadedStrings #-}
--   
--   data Coord = Coord { x :: Double, y :: Double }
--   
--   instance FromJSON Coord where
--       parseJSON (Object v) = Coord
--           <$> v .: "x"
--           <*> v .: "y"
--   
--       -- We do not expect a non-Object value here.
--       -- We could use empty to fail, but typeMismatch
--       -- gives a much more informative error message.
--       parseJSON invalid    =
--           prependFailure "parsing Coord failed, "
--               (typeMismatch "Object" invalid)
--

-- -- For this common case of only being concerned with a single type of -- JSON value, the functions withObject, withScientific, -- etc. are provided. Their use is to be preferred when possible, since -- they are more terse. Using withObject, we can rewrite the above -- instance (assuming the same language extension and data type) as: -- --

--   instance FromJSON Coord where
--       parseJSON = withObject "Coord" $ \v -> Coord
--           <$> v .: "x"
--           <*> v .: "y"
--

-- -- Instead of manually writing your FromJSON instance, there are -- two options to do it automatically: -- --

Data.Aeson.TH provides Template Haskell functions which -- will derive an instance at compile time. The generated instance is -- optimized for your type so it will probably be more efficient than the -- following option.
The compiler can provide a default generic implementation for -- parseJSON.

-- -- To use the second, simply add a deriving Generic -- clause to your datatype and declare a FromJSON instance for -- your datatype without giving a definition for parseJSON. -- -- For example, the previous example can be simplified to just: -- --

--   {-# LANGUAGE DeriveGeneric #-}
--   
--   import GHC.Generics
--   
--   data Coord = Coord { x :: Double, y :: Double } deriving Generic
--   
--   instance FromJSON Coord
--

-- -- or using the DerivingVia extension -- --

--   deriving via Generically Coord instance FromJSON Coord
--

-- -- The default implementation will be equivalent to parseJSON = -- genericParseJSON defaultOptions; if you need -- different options, you can customize the generic decoding by defining: -- --

--   customOptions = defaultOptions
--                   { fieldLabelModifier = map toUpper
--                   }
--   
--   instance FromJSON Coord where
--       parseJSON = genericParseJSON customOptions
--

class FromJSON a -- | Class for string-like datastructures; used by the overloaded string -- extension (-XOverloadedStrings in GHC). class IsString a fromString :: IsString a => String -> a -- | This is the simplest representation of UTC. It consists of the day -- number, and a time offset from midnight. Note that if a day has a leap -- second added to it, it will have 86401 seconds. data UTCTime UTCTime :: Day -> DiffTime -> UTCTime -- | the day [utctDay] :: UTCTime -> Day -- | the time from midnight, 0 <= t < 86401s (because of -- leap-seconds) [utctDayTime] :: UTCTime -> DiffTime -- | This is a length of time, as measured by a clock. Conversion functions -- such as fromInteger and realToFrac will treat it as -- seconds. For example, (0.010 :: DiffTime) corresponds to 10 -- milliseconds. -- -- It has a precision of one picosecond (= 10^-12 s). Enumeration -- functions will treat it as picoseconds. data DiffTime -- | A set of values a. data Set a -- | A class of types that can be fully evaluated. class NFData a -- | The Binary class provides put and get, methods to -- encode and decode a Haskell value to a lazy ByteString. It -- mirrors the Read and Show classes for textual -- representation of Haskell types, and is suitable for serialising -- Haskell values to disk, over the network. -- -- For decoding and generating simple external binary formats (e.g. C -- structures), Binary may be used, but in general is not suitable for -- complex protocols. Instead use the PutM and Get -- primitives directly. -- -- Instances of Binary should satisfy the following property: -- --

--   decode . encode == id
--

-- -- That is, the get and put methods should be the inverse -- of each other. A range of instances are provided for basic Haskell -- types. class Binary t -- | The class of types that can be converted to a hash value. -- -- Minimal implementation: hashWithSalt. -- -- Note: the hash is not guaranteed to be stable across library -- versions, operating systems or architectures. For stable hashing use -- named hashes: SHA256, CRC32 etc. -- -- If you are looking for Hashable instance in time -- package, check time-compat class Eq a => Hashable a -- | The fromMaybe function takes a default value and a Maybe -- value. If the Maybe is Nothing, it returns the default -- value; otherwise, it returns the value contained in the Maybe. -- --

Examples

-- -- Basic usage: -- --

--   >>> fromMaybe "" (Just "Hello, World!")
--   "Hello, World!"
--

-- --

--   >>> fromMaybe "" Nothing
--   ""
--

-- -- Read an integer from a string using readMaybe. If we fail to -- parse an integer, we want to return 0 by default: -- --

--   >>> import Text.Read ( readMaybe )
--   
--   >>> fromMaybe 0 (readMaybe "5")
--   5
--   
--   >>> fromMaybe 0 (readMaybe "")
--   0
--

fromMaybe :: a -> Maybe a -> a module OpenSuse.StripSpace -- | A (quite possibly inefficient) re-implementation of git -- stripspace. This function normalizes a Text buffer to -- conform to the following rules: -- --

All trailing white space is stripped.
Empty lines at the beginning or at the end of the buffer are -- stripped.
Consecutive empty lines between paragraphs are collapsed into -- one.
\r\n line endings are normalized into \n.
If the buffer is not empty, then its last line is terminated by -- \n.
If the buffer is empty (i.e. it contains only white space), then -- it comes out as the empty string.

stripSpace :: Text -> Text module OpenSuse.GuessChangeLog -- | Automatically guess the differences between to releases of a package -- by looking at the change log file provided by upstream. The function -- as arguments the paths of two directories that contain the extracted -- release tarballs. The first arguments ought to point to the older -- release, the second paths ought to point to the updated version. -- -- The function uses the following algorithm to detect the relevant -- changes: -- --

Scan both directories for files that look like they might be -- change logs.
If both directories contain the same candidate file, e.g. -- ChangeLog, then use that.
Compute the differences between the change log files and check -- that all modifications are additions at the top of the file.
Return those additions as Text.

guessChangeLog :: FilePath -> FilePath -> IO GuessedChangeLog data GuessedChangeLog -- | Both releases contained the given change log file, and these files -- differed so that the given text was added at the top of the new one. -- The text undergoes some amount of cleanup, i.e. we'll trim leading -- empty lines at the top, trailing whitespace, and trailing empty lines -- at the end. GuessedChangeLog :: FilePath -> Text -> GuessedChangeLog -- | Neither release contains a change log file. NoChangeLogFiles :: GuessedChangeLog -- | A change log file exists (and its name is returned), but it's -- identical in both releases. In other words, upstream probably forgot -- to document the release. UndocumentedUpdate :: FilePath -> GuessedChangeLog -- | Both releases contain a set of files that look like they might be a -- change log, but their intersection is empty! This happens, for -- example, when upstream has renamed the file. NoCommonChangeLogFiles :: Set FilePath -> Set FilePath -> GuessedChangeLog -- | Multiple change log files exists in both directories. Now, it would -- probably work out okay if we'd just look at the diffs of both of them, -- respectively, but it felt like a good idea to err on the side of -- caution. This case is rare anyways. MoreThanOneChangeLogFile :: Set FilePath -> GuessedChangeLog -- | guessChangelog accepts up to 10 lines of unmodified text at -- the top of the upstream change log file because some people like to -- have a short introduction text there etc. If that header becomes too -- large, however, then we return this error because we expect upstream -- to add text at the top, not in the middle of the file. UnmodifiedTopIsTooLarge :: FilePath -> Word -> GuessedChangeLog -- | This happens when upstream edits the file in ways other than just -- adding at the top. Sometimes people re-format old entries or rewrite -- URLs or fix typos, and in such a case it feels to risky to trust the -- diff. NotJustTopAdditions :: FilePath -> GuessedChangeLog instance GHC.Show.Show OpenSuse.GuessChangeLog.GuessedChangeLog module OpenSuse.Types.EMailAddress -- |

--   >>> mkEMailAddress " accept . full (rfc822) . syntax @ example . org "
--   Just (EMailAddress "accept.full.syntax@example.org")
--

-- --

--   >>> mkEMailAddress "@this@is@not@good@"
--   Nothing
--

-- --

--   >>> prettyShow (fromString "joe @ example.net" :: EMailAddress)
--   "joe@example.net"
--

data EMailAddress -- | Constructor function for e-mail addresses. Returns Nothing if -- the input is syntactically invalid. mkEMailAddress :: String -> Maybe EMailAddress -- | Accessor function for the underlying path of strings. unEMailAddress :: EMailAddress -> String instance Control.DeepSeq.NFData OpenSuse.Types.EMailAddress.EMailAddress instance Data.Binary.Class.Binary OpenSuse.Types.EMailAddress.EMailAddress instance Data.Hashable.Class.Hashable OpenSuse.Types.EMailAddress.EMailAddress instance GHC.Generics.Generic OpenSuse.Types.EMailAddress.EMailAddress instance GHC.Classes.Ord OpenSuse.Types.EMailAddress.EMailAddress instance GHC.Classes.Eq OpenSuse.Types.EMailAddress.EMailAddress instance GHC.Show.Show OpenSuse.Types.EMailAddress.EMailAddress instance Text.Parsec.Class.HasParser OpenSuse.Types.EMailAddress.EMailAddress instance Data.String.IsString OpenSuse.Types.EMailAddress.EMailAddress instance Text.PrettyPrint.HughesPJClass.Pretty OpenSuse.Types.EMailAddress.EMailAddress module OpenSuse.Types.ChangeLog newtype ChangeLog ChangeLog :: [Entry] -> ChangeLog data Entry Entry :: UTCTime -> EMailAddress -> Text -> Entry [changedAt] :: Entry -> UTCTime [changedBy] :: Entry -> EMailAddress [changeDescription] :: Entry -> Text parseEntry :: CharParser st input m Entry parseDashedLine :: CharParser st input m () -- | Note that the input must be terminated by a newline. -- --

--   >>> parseTest parseDateAddressLine "Wed Jun 27 09:25:07 UTC 2018 - foo@example.org\n"
--   (2018-06-27 09:25:07 UTC,EMailAddress "foo@example.org")
--

parseDateAddressLine :: CharParser st input m (UTCTime, EMailAddress) -- | Consume all text until the end of the file or a dashed line is found. -- In the latter case, the dashed line is consumed as well. This is -- unfortunate, but it's how the notFollowedBy combinator works, -- unfortunately, parseDescription :: CharParser st input m String instance GHC.Generics.Generic OpenSuse.Types.ChangeLog.Entry instance GHC.Classes.Ord OpenSuse.Types.ChangeLog.Entry instance GHC.Classes.Eq OpenSuse.Types.ChangeLog.Entry instance GHC.Show.Show OpenSuse.Types.ChangeLog.Entry instance GHC.Base.Monoid OpenSuse.Types.ChangeLog.ChangeLog instance GHC.Base.Semigroup OpenSuse.Types.ChangeLog.ChangeLog instance Control.DeepSeq.NFData OpenSuse.Types.ChangeLog.ChangeLog instance GHC.Generics.Generic OpenSuse.Types.ChangeLog.ChangeLog instance GHC.Classes.Ord OpenSuse.Types.ChangeLog.ChangeLog instance GHC.Classes.Eq OpenSuse.Types.ChangeLog.ChangeLog instance GHC.Show.Show OpenSuse.Types.ChangeLog.ChangeLog instance Text.Parsec.Class.HasParser OpenSuse.Types.ChangeLog.ChangeLog instance Control.DeepSeq.NFData OpenSuse.Types.ChangeLog.Entry instance Text.Parsec.Class.HasParser OpenSuse.Types.ChangeLog.Entry module OpenSuse.Types.Issue data Issue Bsc :: Natural -> Issue Cve :: Natural -> Natural -> Issue parseIssue :: String -> Issue parseCve :: String -> Issue parseBsc :: String -> Issue showIssue :: Issue -> String isCve :: Issue -> Bool isBsc :: Issue -> Bool instance GHC.Generics.Generic OpenSuse.Types.Issue.Issue instance GHC.Classes.Ord OpenSuse.Types.Issue.Issue instance GHC.Classes.Eq OpenSuse.Types.Issue.Issue instance GHC.Show.Show OpenSuse.Types.Issue.Issue instance Data.Hashable.Class.Hashable OpenSuse.Types.Issue.Issue instance Data.Binary.Class.Binary OpenSuse.Types.Issue.Issue instance Control.DeepSeq.NFData OpenSuse.Types.Issue.Issue instance Data.Aeson.Types.FromJSON.FromJSON OpenSuse.Types.Issue.Issue instance Data.Aeson.Types.FromJSON.FromJSONKey OpenSuse.Types.Issue.Issue module OpenSuse.Types.PackageName type PackageName = String module OpenSuse.Types.ProjectId -- | Projects are identified on OBS by a string path. -- --

--   >>> parse "project id" "SUSE:SLE-12-SP2:Update" :: ProjectId
--   ProjectId ["SUSE","SLE-12-SP2","Update"]
--   
--   >>> parseM "project id" "SUSE::SLE-12-SP2" :: Maybe ProjectId
--   Nothing
--   
--   >>> parseM "project id" ":SUSE" :: Maybe ProjectId
--   Nothing
--   
--   >>> parseM "project id" "SUSE:" :: Maybe ProjectId
--   Nothing
--

data ProjectId -- | Constructor function for project identifiers. -- -- TODO: Figure out how to deal with the [] project. mkProjectId :: [String] -> ProjectId -- | Accessor function for the underlying path of strings. unProjectId :: ProjectId -> [String] instance GHC.Base.Monoid OpenSuse.Types.ProjectId.ProjectId instance GHC.Base.Semigroup OpenSuse.Types.ProjectId.ProjectId instance Control.DeepSeq.NFData OpenSuse.Types.ProjectId.ProjectId instance Data.Binary.Class.Binary OpenSuse.Types.ProjectId.ProjectId instance Data.Hashable.Class.Hashable OpenSuse.Types.ProjectId.ProjectId instance GHC.Generics.Generic OpenSuse.Types.ProjectId.ProjectId instance GHC.Classes.Ord OpenSuse.Types.ProjectId.ProjectId instance GHC.Classes.Eq OpenSuse.Types.ProjectId.ProjectId instance GHC.Show.Show OpenSuse.Types.ProjectId.ProjectId instance Data.String.IsString OpenSuse.Types.ProjectId.ProjectId instance Text.PrettyPrint.HughesPJClass.Pretty OpenSuse.Types.ProjectId.ProjectId instance Text.Parsec.Class.HasParser OpenSuse.Types.ProjectId.ProjectId instance Data.Aeson.Types.FromJSON.FromJSON OpenSuse.Types.ProjectId.ProjectId instance Data.Aeson.Types.FromJSON.FromJSONKey OpenSuse.Types.ProjectId.ProjectId instance Data.Aeson.Types.ToJSON.ToJSON OpenSuse.Types.ProjectId.ProjectId instance Data.Aeson.Types.ToJSON.ToJSONKey OpenSuse.Types.ProjectId.ProjectId module OpenSuse.Types.RequestId data RequestId -- | Constructor function for typed request identifiers. mkRequestId :: Natural -> RequestId -- | Accessor function for the underlying natural number. unRequestId :: RequestId -> Natural -- | Type synonym for convenience. type ReleaseRequestId = RequestId -- | Type synonym for convenience. type MaintenanceRequestId = RequestId instance Control.DeepSeq.NFData OpenSuse.Types.RequestId.RequestId instance Data.Binary.Class.Binary OpenSuse.Types.RequestId.RequestId instance Data.Hashable.Class.Hashable OpenSuse.Types.RequestId.RequestId instance GHC.Generics.Generic OpenSuse.Types.RequestId.RequestId instance GHC.Enum.Enum OpenSuse.Types.RequestId.RequestId instance GHC.Classes.Ord OpenSuse.Types.RequestId.RequestId instance GHC.Classes.Eq OpenSuse.Types.RequestId.RequestId instance GHC.Show.Show OpenSuse.Types.RequestId.RequestId instance Data.Aeson.Types.FromJSON.FromJSON OpenSuse.Types.RequestId.RequestId instance Data.Aeson.Types.ToJSON.ToJSON OpenSuse.Types.RequestId.RequestId instance Data.String.IsString OpenSuse.Types.RequestId.RequestId instance Text.PrettyPrint.HughesPJClass.Pretty OpenSuse.Types.RequestId.RequestId instance Text.Parsec.Class.HasParser OpenSuse.Types.RequestId.RequestId module OpenSuse.Types.UserName type UserName = String