Copyright	(c) The University of Glasgow 2001-2009
License	BSD-style (see the file LICENSE)
Maintainer	libraries@haskell.org
Stability	stable
Portability	portable
Safe Haskell	Safe
Language	Haskell2010

Control.DeepSeq

Contents

NFData class
Helper functions
Liftings of the NFData class
- For unary constructors
- For binary constructors

Description

This module provides overloaded functions, such as deepseq and rnf, for fully evaluating data structures (that is, evaluating to "Normal Form").

A typical use is to prevent resource leaks in lazy IO programs, by forcing all characters from a file to be read. For example:

import System.IO
import Control.DeepSeq
import Control.Exception (evaluate)

readFile' :: FilePath -> IO String
readFile' fn = do
    h <- openFile fn ReadMode
    s <- hGetContents h
    evaluate (rnf s)
    hClose h
    return s

Note: The example above should rather be written in terms of bracket to ensure releasing file-descriptors in a timely matter (see the description of force for an example).

deepseq differs from seq as it traverses data structures deeply, for example, seq will evaluate only to the first constructor in the list:

> [1,2,undefined] `seq` 3
3

While deepseq will force evaluation of all the list elements:

> [1,2,undefined] `deepseq` 3
*** Exception: Prelude.undefined

Another common use is to ensure any exceptions hidden within lazy fields of a data structure do not leak outside the scope of the exception handler, or to force evaluation of a data structure in one thread, before passing to another thread (preventing work moving to the wrong threads).

Since: deepseq-1.1.0.0

Synopsis

class NFData a where
deepseq :: NFData a => a -> b -> b
force :: NFData a => a -> a
($!!) :: NFData a => (a -> b) -> a -> b
(<$!!>) :: (Monad m, NFData b) => (a -> b) -> m a -> m b
rwhnf :: a -> ()
class NFData1 f where
rnf1 :: (NFData1 f, NFData a) => f a -> ()
class NFData2 p where
rnf2 :: (NFData2 p, NFData a, NFData b) => p a b -> ()

`NFData` class

class NFData a where Source #

A class of types that can be fully evaluated.

Since: deepseq-1.1.0.0

Methods

rnf :: a -> () Source #

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 !_ = ()

rnf :: (Generic a, GNFData Zero (Rep a)) => a -> () Source #

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

NFData Bool Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Bool -> () Source #
NFData Char Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Char -> () Source #
NFData Double Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Double -> () Source #
NFData Float Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Float -> () Source #
NFData Int Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Int -> () Source #
NFData Int8 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Int8 -> () Source #
NFData Int16 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Int16 -> () Source #
NFData Int32 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Int32 -> () Source #
NFData Int64 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Int64 -> () Source #
NFData Integer Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Integer -> () Source #
NFData Natural Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Natural -> () Source #
NFData Ordering Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Ordering -> () Source #
NFData Word Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Word -> () Source #
NFData Word8 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Word8 -> () Source #
NFData Word16 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Word16 -> () Source #
NFData Word32 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Word32 -> () Source #
NFData Word64 Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Word64 -> () Source #
NFData CallStack Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: CallStack -> () Source #
NFData () Source #
Instance details Defined in Control.DeepSeq Methods rnf :: () -> () Source #
NFData TyCon Source #	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 -> () Source #
NFData Void Source #	Defined as `rnf = absurd`. Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Void -> () Source #
NFData Unique Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Unique -> () Source #
NFData Version Source #	Since: deepseq-1.3.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Version -> () Source #
NFData ThreadId Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: ThreadId -> () Source #
NFData ExitCode Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: ExitCode -> () Source #
NFData MaskingState Source #	Since: deepseq-1.4.4.0
Instance details Defined in Control.DeepSeq Methods rnf :: MaskingState -> () Source #
NFData TypeRep Source #	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 -> () Source #
NFData All Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: All -> () Source #
NFData Any Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Any -> () Source #
NFData CChar Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CChar -> () Source #
NFData CSChar Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CSChar -> () Source #
NFData CUChar Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUChar -> () Source #
NFData CShort Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CShort -> () Source #
NFData CUShort Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUShort -> () Source #
NFData CInt Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CInt -> () Source #
NFData CUInt Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUInt -> () Source #
NFData CLong Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CLong -> () Source #
NFData CULong Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CULong -> () Source #
NFData CLLong Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CLLong -> () Source #
NFData CULLong Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CULLong -> () Source #
NFData CBool Source #	Since: deepseq-1.4.3.0
Instance details Defined in Control.DeepSeq Methods rnf :: CBool -> () Source #
NFData CFloat Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CFloat -> () Source #
NFData CDouble Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CDouble -> () Source #
NFData CPtrdiff Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CPtrdiff -> () Source #
NFData CSize Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CSize -> () Source #
NFData CWchar Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CWchar -> () Source #
NFData CSigAtomic Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CSigAtomic -> () Source #
NFData CClock Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CClock -> () Source #
NFData CTime Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CTime -> () Source #
NFData CUSeconds Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUSeconds -> () Source #
NFData CSUSeconds Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CSUSeconds -> () Source #
NFData CFile Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CFile -> () Source #
NFData CFpos Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CFpos -> () Source #
NFData CJmpBuf Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CJmpBuf -> () Source #
NFData CIntPtr Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CIntPtr -> () Source #
NFData CUIntPtr Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUIntPtr -> () Source #
NFData CIntMax Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CIntMax -> () Source #
NFData CUIntMax Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: CUIntMax -> () Source #
NFData Fingerprint Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Fingerprint -> () Source #
NFData SrcLoc Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: SrcLoc -> () Source #
NFData a => NFData [a] Source #
Instance details Defined in Control.DeepSeq Methods rnf :: [a] -> () Source #
NFData a => NFData (Maybe a) Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Maybe a -> () Source #
NFData a => NFData (Ratio a) Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Ratio a -> () Source #
NFData (Ptr a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: Ptr a -> () Source #
NFData (FunPtr a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: FunPtr a -> () Source #
NFData a => NFData (Complex a) Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Complex a -> () Source #
NFData (Fixed a) Source #	Since: deepseq-1.3.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Fixed a -> () Source #
NFData a => NFData (Min a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: Min a -> () Source #
NFData a => NFData (Max a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: Max a -> () Source #
NFData a => NFData (First a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: First a -> () Source #
NFData a => NFData (Last a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: Last a -> () Source #
NFData m => NFData (WrappedMonoid m) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: WrappedMonoid m -> () Source #
NFData a => NFData (Option a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: Option a -> () Source #
NFData (StableName a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: StableName a -> () Source #
NFData a => NFData (ZipList a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: ZipList a -> () Source #
NFData a => NFData (Identity a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Identity a -> () Source #
NFData (IORef a) Source #	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 -> () Source #
NFData a => NFData (First a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: First a -> () Source #
NFData a => NFData (Last a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Last a -> () Source #
NFData a => NFData (Dual a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Dual a -> () Source #
NFData a => NFData (Sum a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Sum a -> () Source #
NFData a => NFData (Product a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Product a -> () Source #
NFData a => NFData (Down a) Source #	Since: deepseq-1.4.0.0
Instance details Defined in Control.DeepSeq Methods rnf :: Down a -> () Source #
NFData (MVar a) Source #	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 -> () Source #
NFData a => NFData (NonEmpty a) Source #	Since: deepseq-1.4.2.0
Instance details Defined in Control.DeepSeq Methods rnf :: NonEmpty a -> () Source #
NFData (a -> b) Source #	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) -> () Source #
(NFData a, NFData b) => NFData (Either a b) Source #
Instance details Defined in Control.DeepSeq Methods rnf :: Either a b -> () Source #
(NFData a, NFData b) => NFData (a, b) Source #
Instance details Defined in Control.DeepSeq Methods rnf :: (a, b) -> () Source #
(NFData a, NFData b) => NFData (Array a b) Source #
Instance details Defined in Control.DeepSeq Methods

NFData class

Generic NFData deriving

Compatibility with previous deepseq versions

Generic NFData deriving

Compatibility with previous deepseq versions

`NFData` class

`Generic` `NFData` deriving

Compatibility with previous `deepseq` versions

`Generic` `NFData` deriving

Compatibility with previous `deepseq` versions