ClassyPrelude

CorePrelude

module CorePrelude

undefined :: a

Deprecated: It is highly recommended that you either avoid partial functions or provide meaningful error messages

We define our own undefined which is marked as deprecated. This makes it useful to use during development, but lets you more easily get notifications if you accidentally ship partial code in production.

The classy prelude recommendation for when you need to really have a partial function in production is to use error with a very descriptive message so that, in case an exception is thrown, you get more information than Prelude.undefined.

Since 0.5.5

Standard

Monoid

(++) :: Monoid m => m -> m -> m infixr 5

Semigroup

class Semigroup a where

Minimal complete definition

Nothing

Methods

(<>) :: a -> a -> a infixr 6

An associative operation.

(a <> b) <> c = a <> (b <> c)

If a is also a Monoid we further require

(<>) = mappend

sconcat :: NonEmpty a -> a

Reduce a non-empty list with <>

The default definition should be sufficient, but this can be overridden for efficiency.

times1p :: Natural -> a -> a

Repeat a value (n + 1) times.

times1p n a = a <> a <> ... <> a  -- using <> n times

The default definition uses peasant multiplication, exploiting associativity to only require O(log n) uses of <>.

See also timesN.

Instances

Semigroup Ordering

Semigroup ()

Semigroup All

Semigroup Any

Semigroup Text

Semigroup IntSet

Semigroup ByteString

Semigroup ByteString

Semigroup Text

Semigroup Builder

Semigroup ShortByteString

Semigroup Builder

Semigroup Void

Semigroup [a]

Semigroup a => Semigroup (Dual a)

Semigroup (Endo a)

Num a => Semigroup (Sum a)

Num a => Semigroup (Product a)

Semigroup (First a)

Semigroup (Last a)

Semigroup a => Semigroup (Maybe a)

Semigroup (Vector a)

(Hashable a, Eq a) => Semigroup (HashSet a)

Semigroup (Seq a)

Ord a => Semigroup (Set a)

Semigroup (IntMap v)

Semigroup (DList a)

Storable a => Semigroup (Vector a)

Ord a => Semigroup (Min a)

Ord a => Semigroup (Max a)

Semigroup (First a)

Semigroup (Last a)

Monoid m => Semigroup (WrappedMonoid m)

Semigroup a => Semigroup (Option a)

Semigroup (NonEmpty a)

Unbox a => Semigroup (Vector a)

Prim a => Semigroup (Vector a)

Semigroup b => Semigroup (a -> b)

Semigroup (Either a b)

(Semigroup a, Semigroup b) => Semigroup (a, b)

Semigroup a => Semigroup (Const a b)

(Hashable k, Eq k) => Semigroup (HashMap k a)

Ord k => Semigroup (Map k v)

Apply f => Semigroup (Act f a)

GrowingAppend mono => Semigroup (MinLen nat mono)

(Semigroup a, Semigroup b, Semigroup c) => Semigroup (a, b, c)

(Semigroup a, Semigroup b, Semigroup c, Semigroup d) => Semigroup (a, b, c, d)

(Semigroup a, Semigroup b, Semigroup c, Semigroup d, Semigroup e) => Semigroup (a, b, c, d, e)

data WrappedMonoid m :: * -> *

Provide a Semigroup for an arbitrary Monoid.

Instances

Generic1 WrappedMonoid

Bounded a => Bounded (WrappedMonoid a)

Enum a => Enum (WrappedMonoid a)

Eq m => Eq (WrappedMonoid m)

Data m => Data (WrappedMonoid m)

Ord m => Ord (WrappedMonoid m)

Read m => Read (WrappedMonoid m)

Show m => Show (WrappedMonoid m)

Generic (WrappedMonoid m)

Monoid m => Monoid (WrappedMonoid m)

Hashable a => Hashable (WrappedMonoid a)

NFData m => NFData (WrappedMonoid m)

Monoid m => Semigroup (WrappedMonoid m)

Typeable (* -> *) WrappedMonoid

type Rep1 WrappedMonoid = D1 D1WrappedMonoid (C1 C1_0WrappedMonoid (S1 S1_0_0WrappedMonoid Par1))

type Rep (WrappedMonoid m) = D1 D1WrappedMonoid (C1 C1_0WrappedMonoid (S1 S1_0_0WrappedMonoid (Rec0 m)))

Functor

module Data.Functor

Applicative

module Control.Applicative

Monad

module Control.Monad

whenM :: Monad m => m Bool -> m () -> m ()

Only perform the action if the predicate returns True.

Since 0.9.2

unlessM :: Monad m => m Bool -> m () -> m ()

Only perform the action if the predicate returns False.

Since 0.9.2

Mutable references

module Control.Concurrent.MVar.Lifted

module Control.Concurrent.Chan.Lifted

module Control.Concurrent.STM

atomically :: MonadIO m => STM a -> m a

Generalized version of atomically.

alwaysSTM :: STM Bool -> STM ()

Synonym for always.

alwaysSucceedsSTM :: STM a -> STM ()

Synonym for alwaysSucceeds.

retrySTM :: STM a

Synonym for retry.

orElseSTM :: STM a -> STM a -> STM a

Synonym for orElse.

checkSTM :: Bool -> STM ()

Synonym for check.

module Data.IORef.Lifted

module Data.Mutable

Primitive (exported since 0.9.4)

class Monad m => PrimMonad m

Class of monads which can perform primitive state-transformer actions

Minimal complete definition

primitive

Associated Types

type PrimState m :: *

State token type

Instances

PrimMonad IO

PrimMonad (ST s)

PrimMonad m => PrimMonad (IdentityT m)

PrimMonad m => PrimMonad (ListT m)

PrimMonad m => PrimMonad (MaybeT m)

PrimMonad m => PrimMonad (ReaderT r m)

PrimMonad m => PrimMonad (StateT s m)

PrimMonad m => PrimMonad (StateT s m)

PrimMonad m => PrimMonad (ExceptT e m)

(Error e, PrimMonad m) => PrimMonad (ErrorT e m)

(Monoid w, PrimMonad m) => PrimMonad (WriterT w m)

(Monoid w, PrimMonad m) => PrimMonad (WriterT w m)

(Monoid w, PrimMonad m) => PrimMonad (RWST r w s m)

(Monoid w, PrimMonad m) => PrimMonad (RWST r w s m)

type family PrimState m :: *

State token type

Instances

type PrimState IO = RealWorld

type PrimState (ST s) = s

type PrimState (IdentityT m) = PrimState m

type PrimState (ListT m) = PrimState m

type PrimState (MaybeT m) = PrimState m

type PrimState (ReaderT r m) = PrimState m

type PrimState (StateT s m) = PrimState m

type PrimState (StateT s m) = PrimState m

type PrimState (ExceptT e m) = PrimState m

type PrimState (ErrorT e m) = PrimState m

type PrimState (WriterT w m) = PrimState m

type PrimState (WriterT w m) = PrimState m

type PrimState (RWST r w s m) = PrimState m

type PrimState (RWST r w s m) = PrimState m

primToPrim :: (PrimBase m1, PrimMonad m2, (~) * (PrimState m1) (PrimState m2)) => m1 a -> m2 a

Convert a PrimBase to another monad with the same state token.

primToIO :: (PrimBase m, (~) * (PrimState m) RealWorld) => m a -> IO a

Convert a PrimBase with a RealWorld state token to IO

primToST :: PrimBase m => m a -> ST (PrimState m) a

Convert a PrimBase to ST

module Data.Primitive.MutVar

class Prim a

Class of types supporting primitive array operations

Minimal complete definition

sizeOf#, alignment#, indexByteArray#, readByteArray#, writeByteArray#, setByteArray#, indexOffAddr#, readOffAddr#, writeOffAddr#, setOffAddr#

Instances

Prim Char

Prim Double

Prim Float

Prim Int

Prim Int8

Prim Int16

Prim Int32

Prim Int64

Prim Word

Prim Word8

Prim Word16

Prim Word32

Prim Word64

Prim Addr

Debugging

trace :: String -> a -> a

The trace function outputs the trace message given as its first argument, before returning the second argument as its result.

For example, this returns the value of f x but first outputs the message.

trace ("calling f with x = " ++ show x) (f x)

The trace function should only be used for debugging, or for monitoring execution. The function is not referentially transparent: its type indicates that it is a pure function but it has the side effect of outputting the trace message.

traceShow :: Show a => a -> b -> b

Like trace, but uses show on the argument to convert it to a String.

This makes it convenient for printing the values of interesting variables or expressions inside a function. For example here we print the value of the variables x and z:

f x y =
    traceShow (x, z) $ result
  where
    z = ...
    ...

traceId :: String -> String

Since 0.5.9

traceM :: Monad m => String -> m ()

Since 0.5.9

traceShowId :: Show a => a -> a

Since 0.5.9

traceShowM :: (Show a, Monad m) => a -> m ()

Since 0.5.9

assert :: Bool -> a -> a

If the first argument evaluates to True, then the result is the second argument. Otherwise an AssertionFailed exception is raised, containing a String with the source file and line number of the call to assert.

Assertions can normally be turned on or off with a compiler flag (for GHC, assertions are normally on unless optimisation is turned on with -O or the -fignore-asserts option is given). When assertions are turned off, the first argument to assert is ignored, and the second argument is returned as the result.

Time (since 0.6.1)

module Data.Time

defaultTimeLocale :: TimeLocale

Generics (since 0.8.1)

class Generic a

Representable types of kind *. This class is derivable in GHC with the DeriveGeneric flag on.

Minimal complete definition

from, to

Instances

Generic Bool

Generic Char

Generic Double

Generic Float

Generic Int

Generic Ordering

Generic ()

Generic All

Generic Any

Generic Arity

Generic Fixity

Generic Associativity

Generic Void

Generic [a]

Generic (U1 p)

Generic (Par1 p)

Generic (ZipList a)

Generic (Dual a)

Generic (Endo a)

Generic (Sum a)

Generic (Product a)

Generic (First a)

Generic (Last a)

Generic (Maybe a)

Generic (Min a)

Generic (Max a)

Generic (First a)

Generic (Last a)

Generic (WrappedMonoid m)

Generic (Option a)

Generic (NonEmpty a)

Generic (Either a b)

Generic (Rec1 f p)

Generic (a, b)

Generic (Const a b)

Generic (WrappedMonad m a)

Generic (Proxy * t)

Generic (Arg a b)

Typeable (* -> Constraint) Generic

Generic (K1 i c p)

Generic ((:+:) f g p)

Generic ((:*:) f g p)

Generic ((:.:) f g p)

Generic (a, b, c)

Generic (WrappedArrow a b c)

Generic (Tagged k s b)

Generic (M1 i c f p)

Generic (a, b, c, d)

Generic (a, b, c, d, e)

Generic (a, b, c, d, e, f)

Generic (a, b, c, d, e, f, g)

Transformers (since 0.9.4)

newtype Identity a :: * -> *

Identity functor and monad. (a non-strict monad)

Constructors

Identity

Fields

runIdentity :: a

Instances

Monad Identity

Functor Identity

MonadFix Identity

Applicative Identity

Foldable Identity

Traversable Identity

Representable Identity

Comonad Identity

ComonadApply Identity

Keyed Identity

Zip Identity

ZipWithKey Identity

Indexable Identity

Lookup Identity

Adjustable Identity

FoldableWithKey Identity

FoldableWithKey1 Identity

TraversableWithKey Identity

TraversableWithKey1 Identity

Apply Identity

Bind Identity

Eq1 Identity

Ord1 Identity

Read1 Identity

Show1 Identity

MonadBaseControl Identity Identity

Eq a => Eq (Identity a)

Ord a => Ord (Identity a)

Read a => Read (Identity a)

Show a => Show (Identity a)

MonoFunctor (Identity a)

MonoFoldable (Identity a)

Eq a => MonoFoldableEq (Identity a)

Ord a => MonoFoldableOrd (Identity a)

MonoTraversable (Identity a)

MonoPointed (Identity a)

MonoComonad (Identity a)

type Rep Identity = ()

type Key Identity = ()

type StM Identity a = a

type Element (Identity a) = a

class Monad m => MonadReader r m | m -> r where

See examples in Control.Monad.Reader. Note, the partially applied function type (->) r is a simple reader monad. See the instance declaration below.

Minimal complete definition

(ask | reader), local

Methods

ask :: m r

Retrieves the monad environment.

Instances

MonadReader r m => MonadReader r (MaybeT m)

MonadReader r m => MonadReader r (ListT m)

MonadReader r m => MonadReader r (IdentityT m)

MonadReader r ((->) r)

(Representable f, (~) * (Rep f) a) => MonadReader a (Co f)

(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

(Monoid w, MonadReader r m) => MonadReader r (WriterT w m)

MonadReader r m => MonadReader r (StateT s m)

MonadReader r m => MonadReader r (StateT s m)

Monad m => MonadReader r (ReaderT r m)

MonadReader r m => MonadReader r (ExceptT e m)

(Error e, MonadReader r m) => MonadReader r (ErrorT e m)

MonadReader r' m => MonadReader r' (ContT r m)

(Monad m, Monoid w) => MonadReader r (RWST r w s m)

(Monad m, Monoid w) => MonadReader r (RWST r w s m)

ask :: MonadReader r m => m r

Retrieves the monad environment.

newtype ReaderT r m a :: * -> (* -> *) -> * -> *

The reader monad transformer, which adds a read-only environment to the given monad.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

Constructors

ReaderT

Fields

runReaderT :: r -> m a

Instances

Monad m => MonadReader r (ReaderT r m)

MonadBaseControl b m => MonadBaseControl b (ReaderT r m)

MonadTrans (ReaderT r)

MonadTransControl (ReaderT r)

Alternative m => Alternative (ReaderT r m)

Monad m => Monad (ReaderT r m)

Functor m => Functor (ReaderT r m)

MonadFix m => MonadFix (ReaderT r m)

MonadPlus m => MonadPlus (ReaderT r m)

Applicative m => Applicative (ReaderT r m)

Representable m => Representable (ReaderT e m)

MonadIO m => MonadIO (ReaderT r m)

Zip m => Zip (ReaderT e m)

MonadThrow m => MonadThrow (ReaderT r m)

MonadCatch m => MonadCatch (ReaderT r m)

MonadMask m => MonadMask (ReaderT r m)

Keyed m => Keyed (ReaderT e m)

Zip m => Zip (ReaderT e m)

ZipWithKey m => ZipWithKey (ReaderT e m)

Indexable m => Indexable (ReaderT e m)

Lookup m => Lookup (ReaderT e m)

PrimMonad m => PrimMonad (ReaderT r m)

Apply m => Apply (ReaderT e m)

Bind m => Bind (ReaderT e m)

Functor m => MonoFunctor (ReaderT r m a)

Applicative m => MonoPointed (ReaderT r m a)

type StT (ReaderT r) a = a

type Rep (ReaderT e m) = (e, Rep m)

type Key (ReaderT e m) = (e, Key m)

type PrimState (ReaderT r m) = PrimState m

type StM (ReaderT r m) a = ComposeSt (ReaderT r) m a

type Element (ReaderT r m a) = a

type Reader r = ReaderT r Identity

The parameterizable reader monad.

Computations are functions of a shared environment.

The return function ignores the environment, while >>= passes the inherited environment to both subcomputations.

Poly hierarchy

module Data.Foldable

module Data.Traversable

Bifunctor (since 0.10.0)

module Data.Bifunctor

Mono hierarchy

module Data.MonoTraversable

module Data.Sequences

module Data.Sequences.Lazy

module Data.Textual.Encoding

module Data.Containers

module Data.Builder

module Data.MinLen

module Data.ByteVector

I/O

data Handle :: *

Haskell defines operations to read and write characters from and to files, represented by values of type Handle. Each value of this type is a handle: a record used by the Haskell run-time system to manage I/O with file system objects. A handle has at least the following properties:

• whether it manages input or output or both;
• whether it is open, closed or semi-closed;
• whether the object is seekable;
• whether buffering is disabled, or enabled on a line or block basis;
• a buffer (whose length may be zero).

Most handles will also have a current I/O position indicating where the next input or output operation will occur. A handle is readable if it manages only input or both input and output; likewise, it is writable if it manages only output or both input and output. A handle is open when first allocated. Once it is closed it can no longer be used for either input or output, though an implementation cannot re-use its storage while references remain to it. Handles are in the Show and Eq classes. The string produced by showing a handle is system dependent; it should include enough information to identify the handle for debugging. A handle is equal according to == only to itself; no attempt is made to compare the internal state of different handles for equality.

Instances

Eq Handle

Show Handle

Typeable * Handle

stdin :: Handle

A handle managing input from the Haskell program's standard input channel.

stdout :: Handle

A handle managing output to the Haskell program's standard output channel.

stderr :: Handle

A handle managing output to the Haskell program's standard error channel.

Non-standard

List-like classes

map :: Functor f => (a -> b) -> f a -> f b

concat :: (MonoFoldable c, Monoid (Element c)) => c -> Element c

concatMap :: (Monoid m, MonoFoldable c) => (Element c -> m) -> c -> m

foldMap :: (Monoid m, MonoFoldable c) => (Element c -> m) -> c -> m

fold :: (Monoid (Element c), MonoFoldable c) => c -> Element c

length :: MonoFoldable c => c -> Int

null :: MonoFoldable c => c -> Bool

pack :: IsSequence c => [Element c] -> c

unpack :: MonoFoldable c => c -> [Element c]

repack :: (MonoFoldable a, IsSequence b, Element a ~ Element b) => a -> b

Repack from one type to another, dropping to a list in the middle.

repack = pack . unpack.

toList :: MonoFoldable c => c -> [Element c]

mapM_ :: (Monad m, MonoFoldable c) => (Element c -> m ()) -> c -> m ()

sequence_ :: (Monad m, MonoFoldable mono, Element mono ~ m a) => mono -> m ()

forM_ :: (Monad m, MonoFoldable c) => c -> (Element c -> m ()) -> m ()

any :: MonoFoldable c => (Element c -> Bool) -> c -> Bool

all :: MonoFoldable c => (Element c -> Bool) -> c -> Bool

and :: (MonoFoldable mono, Element mono ~ Bool) => mono -> Bool

Since 0.9.2

or :: (MonoFoldable mono, Element mono ~ Bool) => mono -> Bool

Since 0.9.2

foldl' :: MonoFoldable c => (a -> Element c -> a) -> a -> c -> a

foldr :: MonoFoldable c => (Element c -> b -> b) -> b -> c -> b

foldM :: (Monad m, MonoFoldable c) => (a -> Element c -> m a) -> a -> c -> m a

elem :: MonoFoldableEq c => Element c -> c -> Bool

readMay :: (Element c ~ Char, MonoFoldable c, Read a) => c -> Maybe a

intercalate :: (Monoid (Element c), IsSequence c) => Element c -> c -> Element c

zip :: Zip f => forall a b. f a -> f b -> f (a, b)

zip3 :: Zip3 f => forall a b c. f a -> f b -> f c -> f (a, b, c)

zip4 :: Zip4 f => forall a b c d. f a -> f b -> f c -> f d -> f (a, b, c, d)

zip5 :: Zip5 f => forall a b c d e. f a -> f b -> f c -> f d -> f e -> f (a, b, c, d, e)

zip6 :: Zip6 f => forall a b c d e g. f a -> f b -> f c -> f d -> f e -> f g -> f (a, b, c, d, e, g)

zip7 :: Zip7 f => forall a b c d e g h. f a -> f b -> f c -> f d -> f e -> f g -> f h -> f (a, b, c, d, e, g, h)

unzip :: Zip f => forall a b. f (a, b) -> (f a, f b)

unzip3 :: Zip3 f => forall a b c. f (a, b, c) -> (f a, f b, f c)

unzip4 :: Zip4 f => forall a b c d. f (a, b, c, d) -> (f a, f b, f c, f d)

unzip5 :: Zip5 f => forall a b c d e. f (a, b, c, d, e) -> (f a, f b, f c, f d, f e)

unzip6 :: Zip6 f => forall a b c d e g. f (a, b, c, d, e, g) -> (f a, f b, f c, f d, f e, f g)

unzip7 :: Zip7 f => forall a b c d e g h. f (a, b, c, d, e, g, h) -> (f a, f b, f c, f d, f e, f g, f h)

zipWith :: Zip f => forall a b c. (a -> b -> c) -> f a -> f b -> f c

zipWith3 :: Zip3 f => forall a b c d. (a -> b -> c -> d) -> f a -> f b -> f c -> f d

zipWith4 :: Zip4 f => forall a b c d e. (a -> b -> c -> d -> e) -> f a -> f b -> f c -> f d -> f e

zipWith5 :: Zip5 f => forall a b c d e g. (a -> b -> c -> d -> e -> g) -> f a -> f b -> f c -> f d -> f e -> f g

zipWith6 :: Zip6 f => forall a b c d e g h. (a -> b -> c -> d -> e -> g -> h) -> f a -> f b -> f c -> f d -> f e -> f g -> f h

zipWith7 :: Zip7 f => forall a b c d e g h i. (a -> b -> c -> d -> e -> g -> h -> i) -> f a -> f b -> f c -> f d -> f e -> f g -> f h -> f i

hashNub :: (Hashable a, Eq a) => [a] -> [a]

same behavior as nub, but requires Hashable & Eq and is O(n log n)

https://github.com/nh2/haskell-ordnub

ordNub :: Ord a => [a] -> [a]

same behavior as nub, but requires Ord and is O(n log n)

https://github.com/nh2/haskell-ordnub

ordNubBy :: Ord b => (a -> b) -> (a -> a -> Bool) -> [a] -> [a]

same behavior as nubBy, but requires Ord and is O(n log n)

https://github.com/nh2/haskell-ordnub

sortWith :: (Ord a, IsSequence c) => (Element c -> a) -> c -> c

Sort elements using the user supplied function to project something out of each element. Inspired by http://hackage.haskell.org/packages/archive/base/latest/doc/html/GHC-Exts.html#v:sortWith.

compareLength :: (Integral i, MonoFoldable c) => c -> i -> Ordering

sum :: (MonoFoldable c, Num (Element c)) => c -> Element c

product :: (MonoFoldable c, Num (Element c)) => c -> Element c

repeat :: a -> [a]

repeat x is an infinite list, with x the value of every element.

Set-like

(\\) :: SetContainer a => a -> a -> a infixl 9

An alias for difference.

intersect :: SetContainer a => a -> a -> a

An alias for intersection.

unions :: (MonoFoldable c, SetContainer (Element c)) => c -> Element c

Text-like

class Show a where

Conversion of values to readable Strings.

Minimal complete definition: showsPrec or show.

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)".

Minimal complete definition

showsPrec | show

Methods

showsPrec

Arguments

:: Int

the operator precedence of the enclosing context (a number from 0 to 11). Function application has precedence 10.

-> a

the value to be converted to a String

-> 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:

• (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.

show :: a -> String

A specialised variant of showsPrec, using precedence context zero, and returning an ordinary String.

showList :: [a] -> ShowS

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.

Instances

Show Bool

Show Char

Show Double

Show Float

Show Int

Show Int8

Show Int16

Show Int32

Show Int64

Show Integer

Show Ordering

Show Word

Show Word8

Show Word16

Show Word32

Show Word64

Show ()

Show Handle

Show ThreadId

Show HandleType

Show SomeNat

Show SomeSymbol

Show HandlePosn

Show BlockReason

Show ThreadStatus

Show BlockedIndefinitelyOnMVar

Show BlockedIndefinitelyOnSTM

Show Deadlock

Show AssertionFailed

Show SomeAsyncException

Show AsyncException

Show ArrayException

Show ExitCode

Show IOErrorType

Show BufferMode

Show Newline

Show NewlineMode

Show GeneralCategory

Show MaskingState

Show IOException

Show ErrorCall

Show ArithException

Show All

Show Any

Show Arity

Show Fixity

Show Associativity

Show TypeRep

Show TyCon

Show SomeException

Show Text

Show IntSet

Show ByteString

Show ByteString

Show Text

Show ShortByteString

Show TimeLocale

Show FilePath

Show Padding

Show DateFormatSpec

Show LocalTime

Show ZonedTime

Show UTCTime

Show Day

Show Void

Show a => Show [a]

(Integral a, Show a) => Show (Ratio a)

Show (U1 p)

Show p => Show (Par1 p)

Show a => Show (ZipList a)

Show a => Show (Dual a)

Show a => Show (Sum a)

Show a => Show (Product a)

Show a => Show (First a)

Show a => Show (Last a)

Show a => Show (Down a)

Show a => Show (Maybe a)

Show a => Show (Vector a)

Show a => Show (HashSet a)

Show a => Show (Seq a)

Show a => Show (Set a)

Show a => Show (IntMap a)

Show a => Show (Identity a)

Show a => Show (Tree a)

Show a => Show (ViewL a)

Show a => Show (ViewR a)

Show a => Show (DList a)

(Show a, Storable a) => Show (Vector a)

Show a => Show (Min a)

Show a => Show (Max a)

Show a => Show (First a)

Show a => Show (Last a)

Show m => Show (WrappedMonoid m)

Show a => Show (Option a)

Show a => Show (NonEmpty a)

(Show a, Unbox a) => Show (Vector a)

(Show a, Prim a) => Show (Vector a)

(Show a, Show b) => Show (Either a b)

Show (f p) => Show (Rec1 f p)

(Show a, Show b) => Show (a, b)

Show (ST s a)

Show a => Show (Const a b)

(Show k, Show v) => Show (HashMap k v)

(Show k, Show a) => Show (Map k a)

(Show1 f, Show a) => Show (IdentityT f a)

Show mono => Show (MinLen nat mono)

(Show1 m, Show a) => Show (ListT m a)

(Show a, Show b) => Show (Arg a b)

(Show1 g, Show a) => Show (Apply g a)

(Show1 m, Show a) => Show (MaybeT m a)

Typeable (* -> Constraint) Show

Show c => Show (K1 i c p)

(Show (f p), Show (g p)) => Show ((:+:) f g p)

(Show (f p), Show (g p)) => Show ((:*:) f g p)

Show (f (g p)) => Show ((:.:) f g p)

(Show a, Show b, Show c) => Show (a, b, c)

Show (Coercion k a b)

Show ((:~:) k a b)

(Show (f a), Show (g a)) => Show (Coproduct f g a)

(Show e, Show1 m, Show a) => Show (ExceptT e m a)

(Show e, Show1 m, Show a) => Show (ErrorT e m a)

(Show w, Show1 m, Show a) => Show (WriterT w m a)

(Show w, Show1 m, Show a) => Show (WriterT w m a)

(Functor f, Show1 f, Show1 g, Show a) => Show (Compose f g a)

Show b => Show (Tagged k s b)

(Show1 f, Show1 g, Show a) => Show (Product f g a)

Show (f p) => Show (M1 i c f p)

(Show a, Show b, Show c, Show d) => Show (a, b, c, d)

(Show a, Show b, Show c, Show d, Show e) => Show (a, b, c, d, e)

(Show a, Show b, Show c, Show d, Show e, Show f) => Show (a, b, c, d, e, f)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g) => Show (a, b, c, d, e, f, g)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h) => Show (a, b, c, d, e, f, g, h)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i) => Show (a, b, c, d, e, f, g, h, i)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j) => Show (a, b, c, d, e, f, g, h, i, j)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k) => Show (a, b, c, d, e, f, g, h, i, j, k)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l) => Show (a, b, c, d, e, f, g, h, i, j, k, l)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n)

(Show a, Show b, Show c, Show d, Show e, Show f, Show g, Show h, Show i, Show j, Show k, Show l, Show m, Show n, Show o) => Show (a, b, c, d, e, f, g, h, i, j, k, l, m, n, o)

tshow :: Show a => a -> Text

tlshow :: Show a => a -> LText

Case conversion

charToLower :: Char -> Char

Convert a character to lower case.

Character-based case conversion is lossy in comparison to string-based toLower. For instance, İ will be converted to i, instead of i̇.

charToUpper :: Char -> Char

Convert a character to upper case.

Character-based case conversion is lossy in comparison to string-based toUpper. For instance, ß won't be converted to SS.

IO

class IsSequence a => IOData a where

Data which can be read to and from files and handles.

Note that, for lazy sequences, these operations may perform lazy I/O.

Methods

readFile :: MonadIO m => FilePath -> m a

writeFile :: MonadIO m => FilePath -> a -> m ()

getLine :: MonadIO m => m a

hGetContents :: MonadIO m => Handle -> m a

hGetLine :: MonadIO m => Handle -> m a

hPut :: MonadIO m => Handle -> a -> m ()

hPutStrLn :: MonadIO m => Handle -> a -> m ()

hGetChunk :: MonadIO m => Handle -> m a

Instances

IOData Text

IOData ByteString

IOData ByteString

IOData Text

(~) * Char c => IOData [c]

print :: (Show a, MonadIO m) => a -> m ()

hClose :: Handle -> IO ()

Computation hClose hdl makes handle hdl closed. Before the computation finishes, if hdl is writable its buffer is flushed as for hFlush. Performing hClose on a handle that has already been closed has no effect; doing so is not an error. All other operations on a closed handle will fail. If hClose fails for any reason, any further operations (apart from hClose) on the handle will still fail as if hdl had been successfully closed.

FilePath

fpToString :: FilePath -> String

Deprecated: Now same as id

fpFromString :: String -> FilePath

Deprecated: Now same as id

fpToText :: FilePath -> Text

Deprecated: Use pack

Translates a FilePath to a Text This translation is not correct for a (unix) filename which can contain arbitrary (non-unicode) bytes: those bytes will be discarded.

This means you cannot translate the Text back to the original file name.

If you control or otherwise understand the filenames and believe them to be unicode valid consider using fpToTextEx or fpToTextWarn

fpFromText :: Text -> FilePath

Deprecated: Use unpack

fpToTextWarn :: Monad m => FilePath -> m Text

Deprecated: Use pack

Translates a FilePath to a Text

Warns if there are non-unicode sequences in the file name

fpToTextEx :: FilePath -> Text

Deprecated: Use pack

Translates a FilePath to a Text

Throws an exception if there are non-unicode sequences in the file name

Use this to assert that you know a filename will translate properly into a Text. If you created the filename, this should be the case.

Difference lists

data DList a :: * -> *

A difference list is a function that, given a list, returns the original contents of the difference list prepended to the given list.

This structure supports O(1) append and snoc operations on lists, making it very useful for append-heavy uses (esp. left-nested uses of ++), such as logging and pretty printing.

Here is an example using DList as the state type when printing a tree with the Writer monad:

import Control.Monad.Writer
import Data.DList

data Tree a = Leaf a | Branch (Tree a) (Tree a)

flatten_writer :: Tree x -> DList x
flatten_writer = snd . runWriter . flatten
    where
      flatten (Leaf x)     = tell (singleton x)
      flatten (Branch x y) = flatten x >> flatten y

Instances

Alternative DList

Monad DList

Functor DList

MonadPlus DList

Applicative DList

Foldable DList

IsList (DList a)

Eq a => Eq (DList a)

Ord a => Ord (DList a)

Read a => Read (DList a)

Show a => Show (DList a)

IsString (DList Char)

Monoid (DList a)

NFData a => NFData (DList a)

Semigroup (DList a)

SemiSequence (DList a)

IsSequence (DList a)

GrowingAppend (DList a)

MonoFunctor (DList a)

MonoFoldable (DList a)

Eq a => MonoFoldableEq (DList a)

Ord a => MonoFoldableOrd (DList a)

MonoTraversable (DList a)

MonoPointed (DList a)

type Item (DList a) = a

type Index (DList a) = Int

type Element (DList a) = a

asDList :: DList a -> DList a

Force type to a DList

Since 0.11.0

applyDList :: DList a -> [a] -> [a]

Synonym for apply

Since 0.11.0

Exceptions

module Control.Exception.Enclosed

class Monad m => MonadThrow m where

A class for monads in which exceptions may be thrown.

Instances should obey the following law:

throwM e >> x = throwM e

In other words, throwing an exception short-circuits the rest of the monadic computation.

Methods

throwM :: Exception e => e -> m a

Throw an exception. Note that this throws when this action is run in the monad m, not when it is applied. It is a generalization of Control.Exception's throwIO.

Should satisfy the law:

throwM e >> f = throwM e

Instances

MonadThrow []

MonadThrow IO

MonadThrow STM

MonadThrow Maybe

(~) * e SomeException => MonadThrow (Either e)

MonadThrow m => MonadThrow (IdentityT m)

MonadThrow m => MonadThrow (ListT m)

MonadThrow m => MonadThrow (MaybeT m)

Throws exceptions into the base monad.

MonadThrow m => MonadThrow (ContT r m)

MonadThrow m => MonadThrow (ReaderT r m)

MonadThrow m => MonadThrow (StateT s m)

MonadThrow m => MonadThrow (StateT s m)

MonadThrow m => MonadThrow (ExceptT e m)

Throws exceptions into the base monad.

(Error e, MonadThrow m) => MonadThrow (ErrorT e m)

Throws exceptions into the base monad.

(MonadThrow m, Monoid w) => MonadThrow (WriterT w m)

(MonadThrow m, Monoid w) => MonadThrow (WriterT w m)

(MonadThrow m, Monoid w) => MonadThrow (RWST r w s m)

(MonadThrow m, Monoid w) => MonadThrow (RWST r w s m)

class MonadThrow m => MonadCatch m

A class for monads which allow exceptions to be caught, in particular exceptions which were thrown by throwM.

Instances should obey the following law:

catch (throwM e) f = f e

Note that the ability to catch an exception does not guarantee that we can deal with all possible exit points from a computation. Some monads, such as continuation-based stacks, allow for more than just a success/failure strategy, and therefore catch cannot be used by those monads to properly implement a function such as finally. For more information, see MonadMask.

Minimal complete definition

catch

Instances

MonadCatch IO

MonadCatch STM

MonadCatch m => MonadCatch (IdentityT m)

MonadCatch m => MonadCatch (ListT m)

MonadCatch m => MonadCatch (MaybeT m)

Catches exceptions from the base monad.

MonadCatch m => MonadCatch (ReaderT r m)

MonadCatch m => MonadCatch (StateT s m)

MonadCatch m => MonadCatch (StateT s m)

MonadCatch m => MonadCatch (ExceptT e m)

Catches exceptions from the base monad.

(Error e, MonadCatch m) => MonadCatch (ErrorT e m)

Catches exceptions from the base monad.

(MonadCatch m, Monoid w) => MonadCatch (WriterT w m)

(MonadCatch m, Monoid w) => MonadCatch (WriterT w m)

(MonadCatch m, Monoid w) => MonadCatch (RWST r w s m)

(MonadCatch m, Monoid w) => MonadCatch (RWST r w s m)

class MonadCatch m => MonadMask m

A class for monads which provide for the ability to account for all possible exit points from a computation, and to mask asynchronous exceptions. Continuation-based monads, and stacks such as ErrorT e IO which provide for multiple failure modes, are invalid instances of this class.

Note that this package does provide a MonadMask instance for CatchT. This instance is only valid if the base monad provides no ability to provide multiple exit. For example, IO or Either would be invalid base monads, but Reader or State would be acceptable.

Instances should ensure that, in the following code:

f `finally` g

The action g is called regardless of what occurs within f, including async exceptions.

Minimal complete definition

mask, uninterruptibleMask

Instances

MonadMask IO

MonadMask m => MonadMask (IdentityT m)

MonadMask m => MonadMask (ReaderT r m)

MonadMask m => MonadMask (StateT s m)

MonadMask m => MonadMask (StateT s m)

(MonadMask m, Monoid w) => MonadMask (WriterT w m)

(MonadMask m, Monoid w) => MonadMask (WriterT w m)

(MonadMask m, Monoid w) => MonadMask (RWST r w s m)

(MonadMask m, Monoid w) => MonadMask (RWST r w s m)

Force types

Helper functions for situations where type inferer gets confused.

asByteString :: ByteString -> ByteString

asLByteString :: LByteString -> LByteString

asHashMap :: HashMap k v -> HashMap k v

asHashSet :: HashSet a -> HashSet a

asText :: Text -> Text

asLText :: LText -> LText

asList :: [a] -> [a]

asMap :: Map k v -> Map k v

asIntMap :: IntMap v -> IntMap v

asMaybe :: Maybe a -> Maybe a

asSet :: Set a -> Set a

asIntSet :: IntSet -> IntSet

asVector :: Vector a -> Vector a

asUVector :: UVector a -> UVector a

asSVector :: SVector a -> SVector a

asString :: [Char] -> [Char]