Safe Haskell | None |
---|---|

Language | Haskell98 |

BasicPrelude mostly re-exports several key libraries in their entirety. The exception is Data.List, where various functions are replaced by similar versions that are either generalized, operate on Text, or are implemented strictly.

- module CorePrelude
- module Data.List
- module Control.Monad
- class Foldable t where
- elem :: Foldable t => forall a. Eq a => a -> t a -> Bool
- maximum :: Foldable t => forall a. Ord a => t a -> a
- minimum :: Foldable t => forall a. Ord a => t a -> a
- class (Functor t, Foldable t) => Traversable t where
- map :: Functor f => (a -> b) -> f a -> f b
- empty :: Monoid w => w
- (++) :: Monoid w => w -> w -> w
- concat :: Monoid w => [w] -> w
- intercalate :: Monoid w => w -> [w] -> w
- sum :: (Foldable f, Num a) => f a -> a
- product :: (Foldable f, Num a) => f a -> a
- tshow :: Show a => a -> Text
- fromShow :: (Show a, IsString b) => a -> b
- read :: Read a => Text -> a
- readIO :: Read a => Text -> IO a
- readFile :: FilePath -> IO Text
- writeFile :: FilePath -> Text -> IO ()
- appendFile :: FilePath -> Text -> IO ()
- lines :: Text -> [Text]
- words :: Text -> [Text]
- unlines :: [Text] -> Text
- unwords :: [Text] -> Text
- textToString :: Text -> String
- ltextToString :: LText -> String
- fpToText :: FilePath -> Text
- fpFromText :: Text -> FilePath
- fpToString :: FilePath -> String
- encodeUtf8 :: Text -> ByteString
- decodeUtf8 :: ByteString -> Text
- getLine :: IO Text
- getContents :: IO Text
- interact :: (Text -> Text) -> IO ()
- gcd :: Integral a => a -> a -> a
- lcm :: Integral a => a -> a -> a
- class Show a where
- type ShowS = String -> String
- shows :: Show a => a -> ShowS
- showChar :: Char -> ShowS
- showString :: String -> ShowS
- showParen :: Bool -> ShowS -> ShowS
- type ReadS a = String -> [(a, String)]
- readsPrec :: Read a => Int -> ReadS a
- readList :: Read a => ReadS [a]
- reads :: Read a => ReadS a
- readParen :: Bool -> ReadS a -> ReadS a
- lex :: ReadS String
- readMay :: Read a => Text -> Maybe a
- putChar :: Char -> IO ()
- getChar :: IO Char
- readLn :: Read a => IO a

# Module exports

module CorePrelude

module Data.List

module Control.Monad

## Folds and traversals

Data structures that can be folded.

For example, given a data type

data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)

a suitable instance would be

instance Foldable Tree where foldMap f Empty = mempty foldMap f (Leaf x) = f x foldMap f (Node l k r) = foldMap f l `mappend` f k `mappend` foldMap f r

This is suitable even for abstract types, as the monoid is assumed
to satisfy the monoid laws. Alternatively, one could define `foldr`

:

instance Foldable Tree where foldr f z Empty = z foldr f z (Leaf x) = f x z foldr f z (Node l k r) = foldr f (f k (foldr f z r)) l

`Foldable`

instances are expected to satisfy the following laws:

foldr f z t = appEndo (foldMap (Endo . f) t ) z

foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z

fold = foldMap id

`sum`

, `product`

, `maximum`

, and `minimum`

should all be essentially
equivalent to `foldMap`

forms, such as

sum = getSum . foldMap Sum

but may be less defined.

If the type is also a `Functor`

instance, it should satisfy

foldMap f = fold . fmap f

which implies that

foldMap f . fmap g = foldMap (f . g)

foldMap :: Monoid m => (a -> m) -> t a -> m #

Map each element of the structure to a monoid, and combine the results.

foldr :: (a -> b -> b) -> b -> t a -> b #

Right-associative fold of a structure.

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,
`foldr`

can produce a terminating expression from an infinite list.

For a general `Foldable`

structure this should be semantically identical
to,

foldr f z =`foldr`

f z .`toList`

foldr' :: (a -> b -> b) -> b -> t a -> b #

Right-associative fold of a structure, but with strict application of the operator.

foldl :: (b -> a -> b) -> b -> t a -> b #

Left-associative fold of a structure.

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. This means that `foldl'`

will
diverge if given an infinite list.

Also note that if you want an efficient left-fold, you probably want to
use `foldl'`

instead of `foldl`

. The reason for this is that latter does
not force the "inner" results (e.g. `z `

in the above example)
before applying them to the operator (e.g. to `f`

x1`(`

). This results
in a thunk chain `f`

x2)`O(n)`

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`

foldl' :: (b -> a -> b) -> b -> t a -> b #

Left-associative fold of a structure but with strict application of the operator.

This ensures that each step of the fold is forced to weak head normal
form before being applied, avoiding the collection of thunks that would
otherwise occur. This is often what you want to strictly reduce a finite
list to a single, monolithic result (e.g. `length`

).

For a general `Foldable`

structure this should be semantically identical
to,

foldl f z =`foldl'`

f z .`toList`

foldr1 :: (a -> a -> a) -> t a -> a #

A variant of `foldr`

that has no base case,
and thus may only be applied to non-empty structures.

`foldr1`

f =`foldr1`

f .`toList`

foldl1 :: (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.

`foldl1`

f =`foldl1`

f .`toList`

Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.

Returns the size/length of a finite structure as an `Int`

. The
default implementation is optimized for structures that are similar to
cons-lists, because there is no general way to do better.

elem :: Eq a => a -> t a -> Bool infix 4 #

Does the element occur in the structure?

maximum :: Ord a => t a -> a #

The largest element of a non-empty structure.

minimum :: Ord a => t a -> a #

The least element of a non-empty structure.

class (Functor t, Foldable t) => Traversable t where #

Functors representing data structures that can be traversed from left to right.

A definition of `traverse`

must satisfy the following laws:

*naturality*`t .`

for every applicative transformation`traverse`

f =`traverse`

(t . f)`t`

*identity*`traverse`

Identity = Identity*composition*`traverse`

(Compose .`fmap`

g . f) = Compose .`fmap`

(`traverse`

g) .`traverse`

f

A definition of `sequenceA`

must satisfy the following laws:

*naturality*`t .`

for every applicative transformation`sequenceA`

=`sequenceA`

.`fmap`

t`t`

*identity*`sequenceA`

.`fmap`

Identity = Identity*composition*`sequenceA`

.`fmap`

Compose = Compose .`fmap`

`sequenceA`

.`sequenceA`

where an *applicative transformation* is a function

t :: (Applicative f, Applicative g) => f a -> g a

preserving the `Applicative`

operations, i.e.

and the identity functor `Identity`

and composition of functors `Compose`

are defined as

newtype Identity a = Identity a instance Functor Identity where fmap f (Identity x) = Identity (f x) instance Applicative Identity where pure x = Identity x Identity f <*> Identity x = Identity (f x) newtype Compose f g a = Compose (f (g a)) instance (Functor f, Functor g) => Functor (Compose f g) where fmap f (Compose x) = Compose (fmap (fmap f) x) instance (Applicative f, Applicative g) => Applicative (Compose f g) where pure x = Compose (pure (pure x)) Compose f <*> Compose x = Compose ((<*>) <$> f <*> x)

(The naturality law is implied by parametricity.)

Instances are similar to `Functor`

, e.g. given a data type

data Tree a = Empty | Leaf a | Node (Tree a) a (Tree a)

a suitable instance would be

instance Traversable Tree where traverse f Empty = pure Empty traverse f (Leaf x) = Leaf <$> f x traverse f (Node l k r) = Node <$> traverse f l <*> f k <*> traverse f r

This is suitable even for abstract types, as the laws for `<*>`

imply a form of associativity.

The superclass instances should satisfy the following:

- In the
`Functor`

instance,`fmap`

should be equivalent to traversal with the identity applicative functor (`fmapDefault`

). - In the
`Foldable`

instance,`foldMap`

should be equivalent to traversal with a constant applicative functor (`foldMapDefault`

).

traverse :: Applicative f => (a -> f b) -> t a -> f (t b) #

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_`

.

sequenceA :: Applicative f => t (f a) -> f (t a) #

Evaluate each action in the structure from left to right, and
and collect the results. For a version that ignores the results
see `sequenceA_`

.

mapM :: Monad m => (a -> m b) -> t a -> m (t b) #

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_`

.

sequence :: Monad m => t (m a) -> m (t a) #

Evaluate each monadic action in the structure from left to
right, and collect the results. For a version that ignores the
results see `sequence_`

.

# Enhanced exports

## Simpler name for a typeclassed operation

intercalate :: Monoid w => w -> [w] -> w Source #

intercalate = mconcat .: intersperse

## Strict implementation

## Text for Read and Show operations

readIO :: Read a => Text -> IO a Source #

The readIO function is similar to read except that it signals parse failure to the IO monad instead of terminating the program.

## FilePath for file operations

readFile :: FilePath -> IO Text Source #

Read a file and return the contents of the file as Text. The entire file is read strictly.

writeFile :: FilePath -> Text -> IO () Source #

Write Text to a file. The file is truncated to zero length before writing begins.

# Text exports

## Text operations (Pure)

textToString :: Text -> String Source #

ltextToString :: LText -> String Source #

fpToText :: FilePath -> Text Source #

Deprecated: Use Data.Text.pack

This function assumes file paths are encoded in UTF8. If it
cannot decode the `FilePath`

, the result is just an approximation.

Since 0.3.13

fpFromText :: Text -> FilePath Source #

Deprecated: Use Data.Text.unpack

Since 0.3.13

fpToString :: FilePath -> String Source #

Deprecated: Use id

Since 0.3.13

encodeUtf8 :: Text -> ByteString #

Encode text using UTF-8 encoding.

decodeUtf8 :: ByteString -> Text Source #

Note that this is *not* the standard `Data.Text.Encoding.decodeUtf8`

. That
function will throw impure exceptions on any decoding errors. This function
instead uses `decodeLenient`

.

## Text operations (IO)

getContents :: IO Text #

Lazily read all user input on `stdin`

as a single string.

interact :: (Text -> Text) -> IO () #

The `interact`

function takes a function of type `Text -> Text`

as its argument. The entire input from the standard input device is
passed (lazily) to this function as its argument, and the resulting
string is output on the standard output device.

# Miscellaneous prelude re-exports

## Math

gcd :: Integral a => a -> a -> a #

is the non-negative factor of both `gcd`

x y`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,

,
the result may be negative if one of the arguments is `abs`

`minBound`

< 0

(and
necessarily is if the other is `minBound`

`0`

or

) for such types.`minBound`

lcm :: Integral a => a -> a -> a #

is the smallest positive integer that both `lcm`

x y`x`

and `y`

divide.

## Show and Read

Conversion of values to readable `String`

s.

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,

produces the string`show`

(Leaf 1 :^: Leaf 2 :^: Leaf 3)`"Leaf 1 :^: (Leaf 2 :^: Leaf 3)"`

.

showsPrec :: Int -> a -> ShowS #

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:

That is, `readsPrec`

parses the string produced by
`showsPrec`

, and delivers the value that `showsPrec`

started with.

utility function converting a `Char`

to a show function that
simply prepends the character unchanged.

showString :: String -> ShowS #

utility function converting a `String`

to a show function that
simply prepends the string unchanged.

readsPrec :: Read a => Int -> ReadS 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:

That is, `readsPrec`

parses the string produced by
`showsPrec`

, and delivers the value that
`showsPrec`

started with.

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

.) If there is no legal lexeme at the
beginning of the input string, `lex`

"" = [("","")]`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