relude-1.2.0.0: Safe, performant, user-friendly and lightweight Haskell Standard Library
Copyright(c) 2016 Stephen Diehl
(c) 2016-2018 Serokell
(c) 2018-2023 Kowainik
LicenseMIT
MaintainerKowainik <xrom.xkov@gmail.com>
StabilityStable
PortabilityPortable
Safe HaskellSafe
LanguageHaskell2010

Relude.DeepSeq

Contents

Description

This module contains useful functions to evaluate expressions to weak-head normal form (WHNF) or just normal form (NF). Useful to force traces or errors inside monadic computations or to remove space leaks.

Synopsis

Control.DeepSeq reexports

class NFData a where #

A class of types that can be fully evaluated.

Since: deepseq-1.1.0.0

Minimal complete definition

Nothing

Methods

rnf :: a -> () #

rnf should reduce its argument to normal form (that is, fully evaluate all sub-components), and then return ().

Generic NFData deriving

Starting with GHC 7.2, you can automatically derive instances for types possessing a Generic instance.

Note: Generic1 can be auto-derived starting with GHC 7.4

{-# LANGUAGE DeriveGeneric #-}

import GHC.Generics (Generic, Generic1)
import Control.DeepSeq

data Foo a = Foo a String
             deriving (Eq, Generic, Generic1)

instance NFData a => NFData (Foo a)
instance NFData1 Foo

data Colour = Red | Green | Blue
              deriving Generic

instance NFData Colour

Starting with GHC 7.10, the example above can be written more concisely by enabling the new DeriveAnyClass extension:

{-# LANGUAGE DeriveGeneric, DeriveAnyClass #-}

import GHC.Generics (Generic)
import Control.DeepSeq

data Foo a = Foo a String
             deriving (Eq, Generic, Generic1, NFData, NFData1)

data Colour = Red | Green | Blue
              deriving (Generic, NFData)

Compatibility with previous deepseq versions

Prior to version 1.4.0.0, the default implementation of the rnf method was defined as

rnf a = seq a ()

However, starting with deepseq-1.4.0.0, the default implementation is based on DefaultSignatures allowing for more accurate auto-derived NFData instances. If you need the previously used exact default rnf method implementation semantics, use

instance NFData Colour where rnf x = seq x ()

or alternatively

instance NFData Colour where rnf = rwhnf

or

{-# LANGUAGE BangPatterns #-}
instance NFData Colour where rnf !_ = ()

Instances

Instances details
NFData All

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: All -> () #

NFData Any

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Any -> () #

NFData TypeRep

NOTE: Prior to deepseq-1.4.4.0 this instance was only defined for base-4.8.0.0 and later.

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: TypeRep -> () #

NFData Unique

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Unique -> () #

NFData Version

Since: deepseq-1.3.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Version -> () #

NFData Void

Defined as rnf = absurd.

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Void -> () #

NFData CBool

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CBool -> () #

NFData CChar

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CChar -> () #

NFData CClock

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CClock -> () #

NFData CDouble

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CDouble -> () #

NFData CFile

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CFile -> () #

NFData CFloat

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CFloat -> () #

NFData CFpos

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CFpos -> () #

NFData CInt

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CInt -> () #

NFData CIntMax

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CIntMax -> () #

NFData CIntPtr

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CIntPtr -> () #

NFData CJmpBuf

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CJmpBuf -> () #

NFData CLLong

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CLLong -> () #

NFData CLong

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CLong -> () #

NFData CPtrdiff

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CPtrdiff -> () #

NFData CSChar

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CSChar -> () #

NFData CSUSeconds

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CSUSeconds -> () #

NFData CShort

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CShort -> () #

NFData CSigAtomic

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CSigAtomic -> () #

NFData CSize

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CSize -> () #

NFData CTime

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CTime -> () #

NFData CUChar

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUChar -> () #

NFData CUInt

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUInt -> () #

NFData CUIntMax

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUIntMax -> () #

NFData CUIntPtr

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUIntPtr -> () #

NFData CULLong

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CULLong -> () #

NFData CULong

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CULong -> () #

NFData CUSeconds

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUSeconds -> () #

NFData CUShort

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CUShort -> () #

NFData CWchar

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CWchar -> () #

NFData ThreadId

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: ThreadId -> () #

NFData Fingerprint

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Fingerprint -> () #

NFData MaskingState

Since: deepseq-1.4.4.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: MaskingState -> () #

NFData ExitCode

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: ExitCode -> () #

NFData Int16 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Int16 -> () #

NFData Int32 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Int32 -> () #

NFData Int64 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Int64 -> () #

NFData Int8 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Int8 -> () #

NFData CallStack

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: CallStack -> () #

NFData SrcLoc

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: SrcLoc -> () #

NFData Word16 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Word16 -> () #

NFData Word32 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Word32 -> () #

NFData Word64 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Word64 -> () #

NFData Word8 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Word8 -> () #

NFData ByteString 
Instance details

Defined in Data.ByteString.Internal

Methods

rnf :: ByteString -> () #

NFData ByteString 
Instance details

Defined in Data.ByteString.Lazy.Internal

Methods

rnf :: ByteString -> () #

NFData ShortByteString 
Instance details

Defined in Data.ByteString.Short.Internal

Methods

rnf :: ShortByteString -> () #

NFData IntSet 
Instance details

Defined in Data.IntSet.Internal

Methods

rnf :: IntSet -> () #

NFData ByteArray 
Instance details

Defined in Data.Array.Byte

Methods

rnf :: ByteArray -> () #

NFData Ordering 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Ordering -> () #

NFData TyCon

NOTE: Prior to deepseq-1.4.4.0 this instance was only defined for base-4.8.0.0 and later.

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: TyCon -> () #

NFData UnicodeException 
Instance details

Defined in Data.Text.Encoding.Error

Methods

rnf :: UnicodeException -> () #

NFData Integer 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Integer -> () #

NFData Natural

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Natural -> () #

NFData () 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: () -> () #

NFData Bool 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Bool -> () #

NFData Char 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Char -> () #

NFData Double 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Double -> () #

NFData Float 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Float -> () #

NFData Int 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Int -> () #

NFData Word 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Word -> () #

NFData a => NFData (ZipList a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: ZipList a -> () #

NFData a => NFData (Complex a) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Complex a -> () #

NFData a => NFData (Identity a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Identity a -> () #

NFData a => NFData (First a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: First a -> () #

NFData a => NFData (Last a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Last a -> () #

NFData a => NFData (Down a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Down a -> () #

NFData a => NFData (First a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: First a -> () #

NFData a => NFData (Last a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Last a -> () #

NFData a => NFData (Max a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Max a -> () #

NFData a => NFData (Min a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Min a -> () #

NFData m => NFData (WrappedMonoid m)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: WrappedMonoid m -> () #

NFData a => NFData (Dual a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Dual a -> () #

NFData a => NFData (Product a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Product a -> () #

NFData a => NFData (Sum a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Sum a -> () #

NFData (IORef a)

NOTE: Only strict in the reference and not the referenced value.

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: IORef a -> () #

NFData (MVar a)

NOTE: Only strict in the reference and not the referenced value.

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: MVar a -> () #

NFData (FunPtr a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: FunPtr a -> () #

NFData (Ptr a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Ptr a -> () #

NFData a => NFData (Ratio a) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Ratio a -> () #

NFData (StableName a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: StableName a -> () #

NFData a => NFData (IntMap a) 
Instance details

Defined in Data.IntMap.Internal

Methods

rnf :: IntMap a -> () #

NFData a => NFData (Digit a) 
Instance details

Defined in Data.Sequence.Internal

Methods

rnf :: Digit a -> () #

NFData a => NFData (Elem a) 
Instance details

Defined in Data.Sequence.Internal

Methods

rnf :: Elem a -> () #

NFData a => NFData (FingerTree a) 
Instance details

Defined in Data.Sequence.Internal

Methods

rnf :: FingerTree a -> () #

NFData a => NFData (Node a) 
Instance details

Defined in Data.Sequence.Internal

Methods

rnf :: Node a -> () #

NFData a => NFData (Seq a) 
Instance details

Defined in Data.Sequence.Internal

Methods

rnf :: Seq a -> () #

NFData a => NFData (Set a) 
Instance details

Defined in Data.Set.Internal

Methods

rnf :: Set a -> () #

NFData a => NFData (Tree a) 
Instance details

Defined in Data.Tree

Methods

rnf :: Tree a -> () #

NFData (MutableByteArray s) 
Instance details

Defined in Data.Array.Byte

Methods

rnf :: MutableByteArray s -> () #

NFData a => NFData (Hashed a) 
Instance details

Defined in Data.Hashable.Class

Methods

rnf :: Hashed a -> () #

NFData a => NFData (HashSet a) 
Instance details

Defined in Data.HashSet.Internal

Methods

rnf :: HashSet a -> () #

NFData a => NFData (NonEmpty a)

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: NonEmpty a -> () #

NFData a => NFData (Maybe a) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Maybe a -> () #

NFData a => NFData [a] 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: [a] -> () #

(NFData a, NFData b) => NFData (Either a b) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Either a b -> () #

NFData (Fixed a)

Since: deepseq-1.3.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Fixed a -> () #

NFData (Proxy a)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Proxy a -> () #

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

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Arg a b -> () #

(NFData a, NFData b) => NFData (Array a b) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: Array a b -> () #

NFData (STRef s a)

NOTE: Only strict in the reference and not the referenced value.

Since: deepseq-1.4.2.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: STRef s a -> () #

(NFData k, NFData a) => NFData (Map k a) 
Instance details

Defined in Data.Map.Internal

Methods

rnf :: Map k a -> () #

(NFData k, NFData v) => NFData (HashMap k v) 
Instance details

Defined in Data.HashMap.Internal

Methods

rnf :: HashMap k v -> () #

(NFData k, NFData v) => NFData (Leaf k v) 
Instance details

Defined in Data.HashMap.Internal

Methods

rnf :: Leaf k v -> () #

NFData (a -> b)

This instance is for convenience and consistency with seq. This assumes that WHNF is equivalent to NF for functions.

Since: deepseq-1.3.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a -> b) -> () #

(NFData a, NFData b) => NFData (a, b) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a, b) -> () #

NFData a => NFData (Const a b)

Since: deepseq-1.4.0.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Const a b -> () #

NFData (a :~: b)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a :~: b) -> () #

(NFData a1, NFData a2, NFData a3) => NFData (a1, a2, a3) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3) -> () #

(NFData1 f, NFData1 g, NFData a) => NFData (Product f g a)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Product f g a -> () #

(NFData1 f, NFData1 g, NFData a) => NFData (Sum f g a)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Sum f g a -> () #

NFData (a :~~: b)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a :~~: b) -> () #

(NFData a1, NFData a2, NFData a3, NFData a4) => NFData (a1, a2, a3, a4) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4) -> () #

(NFData1 f, NFData1 g, NFData a) => NFData (Compose f g a)

Since: deepseq-1.4.3.0

Instance details

Defined in Control.DeepSeq

Methods

rnf :: Compose f g a -> () #

(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5) => NFData (a1, a2, a3, a4, a5) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4, a5) -> () #

(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6) => NFData (a1, a2, a3, a4, a5, a6) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4, a5, a6) -> () #

(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7) => NFData (a1, a2, a3, a4, a5, a6, a7) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4, a5, a6, a7) -> () #

(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8) => NFData (a1, a2, a3, a4, a5, a6, a7, a8) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4, a5, a6, a7, a8) -> () #

(NFData a1, NFData a2, NFData a3, NFData a4, NFData a5, NFData a6, NFData a7, NFData a8, NFData a9) => NFData (a1, a2, a3, a4, a5, a6, a7, a8, a9) 
Instance details

Defined in Control.DeepSeq

Methods

rnf :: (a1, a2, a3, a4, a5, a6, a7, a8, a9) -> () #

deepseq :: NFData a => a -> b -> b #

deepseq: fully evaluates the first argument, before returning the second.

The name deepseq is used to illustrate the relationship to seq: where seq is shallow in the sense that it only evaluates the top level of its argument, deepseq traverses the entire data structure evaluating it completely.

deepseq can be useful for forcing pending exceptions, eradicating space leaks, or forcing lazy I/O to happen. It is also useful in conjunction with parallel Strategies (see the parallel package).

There is no guarantee about the ordering of evaluation. The implementation may evaluate the components of the structure in any order or in parallel. To impose an actual order on evaluation, use pseq from Control.Parallel in the parallel package.

Since: deepseq-1.1.0.0

force :: NFData a => a -> a #

a variant of deepseq that is useful in some circumstances:

force x = x `deepseq` x

force x fully evaluates x, and then returns it. Note that force x only performs evaluation when the value of force x itself is demanded, so essentially it turns shallow evaluation into deep evaluation.

force can be conveniently used in combination with ViewPatterns:

{-# LANGUAGE BangPatterns, ViewPatterns #-}
import Control.DeepSeq

someFun :: ComplexData -> SomeResult
someFun (force -> !arg) = {- 'arg' will be fully evaluated -}

Another useful application is to combine force with evaluate in order to force deep evaluation relative to other IO operations:

import Control.Exception (evaluate)
import Control.DeepSeq

main = do
  result <- evaluate $ force $ pureComputation
  {- 'result' will be fully evaluated at this point -}
  return ()

Finally, here's an exception safe variant of the readFile' example:

readFile' :: FilePath -> IO String
readFile' fn = bracket (openFile fn ReadMode) hClose $ \h ->
                       evaluate . force =<< hGetContents h

Since: deepseq-1.2.0.0

($!!) :: NFData a => (a -> b) -> a -> b infixr 0 #

the deep analogue of $!. In the expression f $!! x, x is fully evaluated before the function f is applied to it.

Since: deepseq-1.2.0.0

Evaluation

evaluateNF :: (NFData a, MonadIO m) => a -> m a Source #

Alias for evaluateWHNF . force with a clearer name.

>>> let list = [1..5] :: [Int]
>>> :sprint list
list = _
>>> () <$ evaluateNF list
>>> :sprint list
list = [1,2,3,4,5]

evaluateNF_ :: (NFData a, MonadIO m) => a -> m () Source #

Alias for evaluateWHNF . rnf. Similar to evaluateNF but discards the resulting value.

>>> let list = [1..5] :: [Int]
>>> :sprint list
list = _
>>> evaluateNF_ list
>>> :sprint list
list = [1,2,3,4,5]

evaluateWHNF :: MonadIO m => a -> m a Source #

Lifted alias for evaluate with a clearer name.

>>> let list = [1..5] :: [Int]
>>> :sprint list
list = _
>>> () <$ evaluateWHNF list
>>> :sprint list
list = 1 : _

evaluateWHNF_ :: MonadIO m => a -> m () Source #

Like evaluateWHNF but discards value.

>>> let list = [1..5] :: [Int]
>>> :sprint list
list = _
>>> evaluateWHNF_ list
>>> :sprint list
list = 1 : _