Copyright	(c) 2016 Stephen Diehl (c) 2016-2018 Serokell (c) 2018-2023 Kowainik
License	MIT
Maintainer	Kowainik <xrom.xkov@gmail.com>
Stability	Stable
Portability	Portable
Safe Haskell	Safe
Language	Haskell2010

Relude.DeepSeq

Contents

Control.DeepSeq reexports
Evaluation

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

class NFData a where
- rnf :: a -> ()
deepseq :: NFData a => a -> b -> b
force :: NFData a => a -> a
($!!) :: NFData a => (a -> b) -> a -> b
evaluateNF :: (NFData a, MonadIO m) => a -> m a
evaluateNF_ :: (NFData a, MonadIO m) => a -> m ()
evaluateWHNF :: MonadIO m => a -> m a
evaluateWHNF_ :: MonadIO m => a -> m ()

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 : _

Control.DeepSeq reexports

Generic NFData deriving

Compatibility with previous deepseq versions

Instances

Evaluation

`Generic` `NFData` deriving

Compatibility with previous `deepseq` versions