{-
NOTA BENE: Do NOT use ($) anywhere in this module! The type of ($) is
slightly magical (it can return unlifted types), and it is wired in.
But, it is also *defined* in this module, with a non-magical type.
GHC gets terribly confused (and *hangs*) if you try to use ($) in this
module, because it has different types in different scenarios.
This is not a problem in general, because the type ($), being wired in, is not
written out to the interface file, so importing files don't get confused.
The problem is only if ($) is used here. So don't!
---------------------------------------------
The overall structure of the GHC Prelude is a bit tricky.
a) We want to avoid "orphan modules", i.e. ones with instance
decls that don't belong either to a tycon or a class
defined in the same module
b) We want to avoid giant modules
So the rough structure is as follows, in (linearised) dependency order
GHC.Prim Has no implementation. It defines built-in things, and
by importing it you bring them into scope.
The source file is GHC.Prim.hi-boot, which is just
copied to make GHC.Prim.hi
GHC.Base Classes: Eq, Ord, Functor, Monad
Types: list, (), Int, Bool, Ordering, Char, String
Data.Tuple Types: tuples, plus instances for GHC.Base classes
GHC.Show Class: Show, plus instances for GHC.Base/GHC.Tup types
GHC.Enum Class: Enum, plus instances for GHC.Base/GHC.Tup types
Data.Maybe Type: Maybe, plus instances for GHC.Base classes
GHC.List List functions
GHC.Num Class: Num, plus instances for Int
Type: Integer, plus instances for all classes so far (Eq, Ord, Num, Show)
Integer is needed here because it is mentioned in the signature
of 'fromInteger' in class Num
GHC.Real Classes: Real, Integral, Fractional, RealFrac
plus instances for Int, Integer
Types: Ratio, Rational
plus instances for classes so far
Rational is needed here because it is mentioned in the signature
of 'toRational' in class Real
GHC.ST The ST monad, instances and a few helper functions
Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
GHC.Arr Types: Array, MutableArray, MutableVar
Arrays are used by a function in GHC.Float
GHC.Float Classes: Floating, RealFloat
Types: Float, Double, plus instances of all classes so far
This module contains everything to do with floating point.
It is a big module (900 lines)
With a bit of luck, many modules can be compiled without ever reading GHC.Float.hi
Other Prelude modules are much easier with fewer complex dependencies.
-}
{-# LANGUAGE Unsafe #-}
{-# LANGUAGE CPP
, NoImplicitPrelude
, BangPatterns
, ExplicitForAll
, MagicHash
, UnboxedTuples
, ExistentialQuantification
, RankNTypes
#-}
-- -Wno-orphans is needed for things like:
-- Orphan rule: "x# -# x#" ALWAYS forall x# :: Int# -# x# x# = 0
{-# OPTIONS_GHC -Wno-orphans #-}
{-# OPTIONS_HADDOCK hide #-}
-----------------------------------------------------------------------------
-- |
-- Module : GHC.Base
-- Copyright : (c) The University of Glasgow, 1992-2002
-- License : see libraries/base/LICENSE
--
-- Maintainer : cvs-ghc@haskell.org
-- Stability : internal
-- Portability : non-portable (GHC extensions)
--
-- Basic data types and classes.
--
-----------------------------------------------------------------------------
#include "MachDeps.h"
module GHC.Base
(
module GHC.Base,
module GHC.Classes,
module GHC.CString,
module GHC.Magic,
module GHC.Types,
module GHC.Prim, -- Re-export GHC.Prim and [boot] GHC.Err,
-- to avoid lots of people having to
module GHC.Err -- import it explicitly
)
where
import GHC.Types
import GHC.Classes
import GHC.CString
import GHC.Magic
import GHC.Prim
import GHC.Err
import {-# SOURCE #-} GHC.IO (failIO,mplusIO)
import GHC.Tuple () -- Note [Depend on GHC.Tuple]
import GHC.Integer () -- Note [Depend on GHC.Integer]
infixr 9 .
infixr 5 ++
infixl 4 <$
infixl 1 >>, >>=
infixr 1 =<<
infixr 0 $, $!
infixl 4 <*>, <*, *>, <**>
default () -- Double isn't available yet
{-
Note [Depend on GHC.Integer]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The Integer type is special because TidyPgm uses
GHC.Integer.Type.mkInteger to construct Integer literal values
Currently it reads the interface file whether or not the current
module *has* any Integer literals, so it's important that
GHC.Integer.Type (in package integer-gmp or integer-simple) is
compiled before any other module. (There's a hack in GHC to disable
this for packages ghc-prim, integer-gmp, integer-simple, which aren't
allowed to contain any Integer literals.)
Likewise we implicitly need Integer when deriving things like Eq
instances.
The danger is that if the build system doesn't know about the dependency
on Integer, it'll compile some base module before GHC.Integer.Type,
resulting in:
Failed to load interface for ‘GHC.Integer.Type’
There are files missing in the ‘integer-gmp’ package,
Bottom line: we make GHC.Base depend on GHC.Integer; and everything
else either depends on GHC.Base, or does not have NoImplicitPrelude
(and hence depends on Prelude).
Note [Depend on GHC.Tuple]
~~~~~~~~~~~~~~~~~~~~~~~~~~
Similarly, tuple syntax (or ()) creates an implicit dependency on
GHC.Tuple, so we use the same rule as for Integer --- see Note [Depend on
GHC.Integer] --- to explain this to the build system. We make GHC.Base
depend on GHC.Tuple, and everything else depends on GHC.Base or Prelude.
-}
#if 0
-- for use when compiling GHC.Base itself doesn't work
data Bool = False | True
data Ordering = LT | EQ | GT
data Char = C# Char#
type String = [Char]
data Int = I# Int#
data () = ()
data [] a = MkNil
not True = False
(&&) True True = True
otherwise = True
build = errorWithoutStackTrace "urk"
foldr = errorWithoutStackTrace "urk"
#endif
-- | The 'Maybe' type encapsulates an optional value. A value of type
-- @'Maybe' a@ either contains a value of type @a@ (represented as @'Just' a@),
-- or it is empty (represented as 'Nothing'). Using 'Maybe' is a good way to
-- deal with errors or exceptional cases without resorting to drastic
-- measures such as 'error'.
--
-- The 'Maybe' type is also a monad. It is a simple kind of error
-- monad, where all errors are represented by 'Nothing'. A richer
-- error monad can be built using the 'Data.Either.Either' type.
--
data Maybe a = Nothing | Just a
deriving (Eq, Ord)
-- | The class of monoids (types with an associative binary operation that
-- has an identity). Instances should satisfy the following laws:
--
-- * @mappend mempty x = x@
--
-- * @mappend x mempty = x@
--
-- * @mappend x (mappend y z) = mappend (mappend x y) z@
--
-- * @mconcat = 'foldr' mappend mempty@
--
-- The method names refer to the monoid of lists under concatenation,
-- but there are many other instances.
--
-- Some types can be viewed as a monoid in more than one way,
-- e.g. both addition and multiplication on numbers.
-- In such cases we often define @newtype@s and make those instances
-- of 'Monoid', e.g. 'Sum' and 'Product'.
class Monoid a where
mempty :: a
-- ^ Identity of 'mappend'
mappend :: a -> a -> a
-- ^ An associative operation
mconcat :: [a] -> a
-- ^ Fold a list using the monoid.
-- For most types, the default definition for 'mconcat' will be
-- used, but the function is included in the class definition so
-- that an optimized version can be provided for specific types.
mconcat = foldr mappend mempty
-- | @since 2.01
instance Monoid [a] where
{-# INLINE mempty #-}
mempty = []
{-# INLINE mappend #-}
mappend = (++)
{-# INLINE mconcat #-}
mconcat xss = [x | xs <- xss, x <- xs]
-- See Note: [List comprehensions and inlining]
{-
Note: [List comprehensions and inlining]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The list monad operations are traditionally described in terms of concatMap:
xs >>= f = concatMap f xs
Similarly, mconcat for lists is just concat. Here in Base, however, we don't
have concatMap, and we'll refrain from adding it here so it won't have to be
hidden in imports. Instead, we use GHC's list comprehension desugaring
mechanism to define mconcat and the Applicative and Monad instances for lists.
We mark them INLINE because the inliner is not generally too keen to inline
build forms such as the ones these desugar to without our insistence. Defining
these using list comprehensions instead of foldr has an additional potential
benefit, as described in compiler/deSugar/DsListComp.lhs: if optimizations
needed to make foldr/build forms efficient are turned off, we'll get reasonably
efficient translations anyway.
-}
-- | @since 2.01
instance Monoid b => Monoid (a -> b) where
mempty _ = mempty
mappend f g x = f x `mappend` g x
-- | @since 2.01
instance Monoid () where
-- Should it be strict?
mempty = ()
_ `mappend` _ = ()
mconcat _ = ()
-- | @since 2.01
instance (Monoid a, Monoid b) => Monoid (a,b) where
mempty = (mempty, mempty)
(a1,b1) `mappend` (a2,b2) =
(a1 `mappend` a2, b1 `mappend` b2)
-- | @since 2.01
instance (Monoid a, Monoid b, Monoid c) => Monoid (a,b,c) where
mempty = (mempty, mempty, mempty)
(a1,b1,c1) `mappend` (a2,b2,c2) =
(a1 `mappend` a2, b1 `mappend` b2, c1 `mappend` c2)
-- | @since 2.01
instance (Monoid a, Monoid b, Monoid c, Monoid d) => Monoid (a,b,c,d) where
mempty = (mempty, mempty, mempty, mempty)
(a1,b1,c1,d1) `mappend` (a2,b2,c2,d2) =
(a1 `mappend` a2, b1 `mappend` b2,
c1 `mappend` c2, d1 `mappend` d2)
-- | @since 2.01
instance (Monoid a, Monoid b, Monoid c, Monoid d, Monoid e) =>
Monoid (a,b,c,d,e) where
mempty = (mempty, mempty, mempty, mempty, mempty)
(a1,b1,c1,d1,e1) `mappend` (a2,b2,c2,d2,e2) =
(a1 `mappend` a2, b1 `mappend` b2, c1 `mappend` c2,
d1 `mappend` d2, e1 `mappend` e2)
-- lexicographical ordering
-- | @since 2.01
instance Monoid Ordering where
mempty = EQ
LT `mappend` _ = LT
EQ `mappend` y = y
GT `mappend` _ = GT
-- | Lift a semigroup into 'Maybe' forming a 'Monoid' according to
-- : \"Any semigroup @S@ may be
-- turned into a monoid simply by adjoining an element @e@ not in @S@
-- and defining @e*e = e@ and @e*s = s = s*e@ for all @s ∈ S@.\" Since
-- there is no \"Semigroup\" typeclass providing just 'mappend', we
-- use 'Monoid' instead.
--
-- @since 2.01
instance Monoid a => Monoid (Maybe a) where
mempty = Nothing
Nothing `mappend` m = m
m `mappend` Nothing = m
Just m1 `mappend` Just m2 = Just (m1 `mappend` m2)
-- | @since 2.01
instance Monoid a => Applicative ((,) a) where
pure x = (mempty, x)
(u, f) <*> (v, x) = (u `mappend` v, f x)
-- | @since 4.9.0.0
instance Monoid a => Monad ((,) a) where
(u, a) >>= k = case k a of (v, b) -> (u `mappend` v, b)
-- | @since 4.9.0.0
instance Monoid a => Monoid (IO a) where
mempty = pure mempty
mappend = liftA2 mappend
{- | The 'Functor' class is used for types that can be mapped over.
Instances of 'Functor' should satisfy the following laws:
> fmap id == id
> fmap (f . g) == fmap f . fmap g
The instances of 'Functor' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
satisfy these laws.
-}
class Functor f where
fmap :: (a -> b) -> f a -> f b
-- | Replace all locations in the input with the same value.
-- The default definition is @'fmap' . 'const'@, but this may be
-- overridden with a more efficient version.
(<$) :: a -> f b -> f a
(<$) = fmap . const
-- | A functor with application, providing operations to
--
-- * embed pure expressions ('pure'), and
--
-- * sequence computations and combine their results ('<*>').
--
-- A minimal complete definition must include implementations of these
-- functions satisfying the following laws:
--
-- [/identity/]
--
-- @'pure' 'id' '<*>' v = v@
--
-- [/composition/]
--
-- @'pure' (.) '<*>' u '<*>' v '<*>' w = u '<*>' (v '<*>' w)@
--
-- [/homomorphism/]
--
-- @'pure' f '<*>' 'pure' x = 'pure' (f x)@
--
-- [/interchange/]
--
-- @u '<*>' 'pure' y = 'pure' ('$' y) '<*>' u@
--
-- The other methods have the following default definitions, which may
-- be overridden with equivalent specialized implementations:
--
-- * @u '*>' v = 'pure' ('const' 'id') '<*>' u '<*>' v@
--
-- * @u '<*' v = 'pure' 'const' '<*>' u '<*>' v@
--
-- As a consequence of these laws, the 'Functor' instance for @f@ will satisfy
--
-- * @'fmap' f x = 'pure' f '<*>' x@
--
-- If @f@ is also a 'Monad', it should satisfy
--
-- * @'pure' = 'return'@
--
-- * @('<*>') = 'ap'@
--
-- (which implies that 'pure' and '<*>' satisfy the applicative functor laws).
class Functor f => Applicative f where
-- | Lift a value.
pure :: a -> f a
-- | Sequential application.
(<*>) :: f (a -> b) -> f a -> f b
-- | Sequence actions, discarding the value of the first argument.
(*>) :: f a -> f b -> f b
a1 *> a2 = (id <$ a1) <*> a2
-- This is essentially the same as liftA2 (const id), but if the
-- Functor instance has an optimized (<$), we want to use that instead.
-- | Sequence actions, discarding the value of the second argument.
(<*) :: f a -> f b -> f a
(<*) = liftA2 const
-- | A variant of '<*>' with the arguments reversed.
(<**>) :: Applicative f => f a -> f (a -> b) -> f b
(<**>) = liftA2 (flip ($))
-- | Lift a function to actions.
-- This function may be used as a value for `fmap` in a `Functor` instance.
liftA :: Applicative f => (a -> b) -> f a -> f b
liftA f a = pure f <*> a
-- Caution: since this may be used for `fmap`, we can't use the obvious
-- definition of liftA = fmap.
-- | Lift a binary function to actions.
liftA2 :: Applicative f => (a -> b -> c) -> f a -> f b -> f c
liftA2 f a b = fmap f a <*> b
-- | Lift a ternary function to actions.
liftA3 :: Applicative f => (a -> b -> c -> d) -> f a -> f b -> f c -> f d
liftA3 f a b c = fmap f a <*> b <*> c
{-# INLINABLE liftA #-}
{-# SPECIALISE liftA :: (a1->r) -> IO a1 -> IO r #-}
{-# SPECIALISE liftA :: (a1->r) -> Maybe a1 -> Maybe r #-}
{-# INLINABLE liftA2 #-}
{-# SPECIALISE liftA2 :: (a1->a2->r) -> IO a1 -> IO a2 -> IO r #-}
{-# SPECIALISE liftA2 :: (a1->a2->r) -> Maybe a1 -> Maybe a2 -> Maybe r #-}
{-# INLINABLE liftA3 #-}
{-# SPECIALISE liftA3 :: (a1->a2->a3->r) -> IO a1 -> IO a2 -> IO a3 -> IO r #-}
{-# SPECIALISE liftA3 :: (a1->a2->a3->r) ->
Maybe a1 -> Maybe a2 -> Maybe a3 -> Maybe r #-}
-- | The 'join' function is the conventional monad join operator. It
-- is used to remove one level of monadic structure, projecting its
-- bound argument into the outer level.
join :: (Monad m) => m (m a) -> m a
join x = x >>= id
{- | The 'Monad' class defines the basic operations over a /monad/,
a concept from a branch of mathematics known as /category theory/.
From the perspective of a Haskell programmer, however, it is best to
think of a monad as an /abstract datatype/ of actions.
Haskell's @do@ expressions provide a convenient syntax for writing
monadic expressions.
Instances of 'Monad' should satisfy the following laws:
* @'return' a '>>=' k = k a@
* @m '>>=' 'return' = m@
* @m '>>=' (\x -> k x '>>=' h) = (m '>>=' k) '>>=' h@
Furthermore, the 'Monad' and 'Applicative' operations should relate as follows:
* @'pure' = 'return'@
* @('<*>') = 'ap'@
The above laws imply:
* @'fmap' f xs = xs '>>=' 'return' . f@
* @('>>') = ('*>')@
and that 'pure' and ('<*>') satisfy the applicative functor laws.
The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
defined in the "Prelude" satisfy these laws.
-}
class Applicative m => Monad m where
-- | Sequentially compose two actions, passing any value produced
-- by the first as an argument to the second.
(>>=) :: forall a b. m a -> (a -> m b) -> m b
-- | Sequentially compose two actions, discarding any value produced
-- by the first, like sequencing operators (such as the semicolon)
-- in imperative languages.
(>>) :: forall a b. m a -> m b -> m b
m >> k = m >>= \_ -> k -- See Note [Recursive bindings for Applicative/Monad]
{-# INLINE (>>) #-}
-- | Inject a value into the monadic type.
return :: a -> m a
return = pure
-- | Fail with a message. This operation is not part of the
-- mathematical definition of a monad, but is invoked on pattern-match
-- failure in a @do@ expression.
--
-- As part of the MonadFail proposal (MFP), this function is moved
-- to its own class 'MonadFail' (see "Control.Monad.Fail" for more
-- details). The definition here will be removed in a future
-- release.
fail :: String -> m a
fail s = errorWithoutStackTrace s
{- Note [Recursive bindings for Applicative/Monad]
~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~
The original Applicative/Monad proposal stated that after
implementation, the designated implementation of (>>) would become
(>>) :: forall a b. m a -> m b -> m b
(>>) = (*>)
by default. You might be inclined to change this to reflect the stated
proposal, but you really shouldn't! Why? Because people tend to define
such instances the /other/ way around: in particular, it is perfectly
legitimate to define an instance of Applicative (*>) in terms of (>>),
which would lead to an infinite loop for the default implementation of
Monad! And people do this in the wild.
This turned into a nasty bug that was tricky to track down, and rather
than eliminate it everywhere upstream, it's easier to just retain the
original default.
-}
-- | Same as '>>=', but with the arguments interchanged.
{-# SPECIALISE (=<<) :: (a -> [b]) -> [a] -> [b] #-}
(=<<) :: Monad m => (a -> m b) -> m a -> m b
f =<< x = x >>= f
-- | Conditional execution of 'Applicative' expressions. For example,
--
-- > when debug (putStrLn "Debugging")
--
-- will output the string @Debugging@ if the Boolean value @debug@
-- is 'True', and otherwise do nothing.
when :: (Applicative f) => Bool -> f () -> f ()
{-# INLINABLE when #-}
{-# SPECIALISE when :: Bool -> IO () -> IO () #-}
{-# SPECIALISE when :: Bool -> Maybe () -> Maybe () #-}
when p s = if p then s else pure ()
-- | Evaluate each action in the sequence from left to right,
-- and collect the results.
sequence :: Monad m => [m a] -> m [a]
{-# INLINE sequence #-}
sequence = mapM id
-- Note: [sequence and mapM]
-- | @'mapM' f@ is equivalent to @'sequence' . 'map' f@.
mapM :: Monad m => (a -> m b) -> [a] -> m [b]
{-# INLINE mapM #-}
mapM f as = foldr k (return []) as
where
k a r = do { x <- f a; xs <- r; return (x:xs) }
{-
Note: [sequence and mapM]
~~~~~~~~~~~~~~~~~~~~~~~~~
Originally, we defined
mapM f = sequence . map f
This relied on list fusion to produce efficient code for mapM, and led to
excessive allocation in cryptarithm2. Defining
sequence = mapM id
relies only on inlining a tiny function (id) and beta reduction, which tends to
be a more reliable aspect of simplification. Indeed, this does not lead to
similar problems in nofib.
-}
-- | Promote a function to a monad.
liftM :: (Monad m) => (a1 -> r) -> m a1 -> m r
liftM f m1 = do { x1 <- m1; return (f x1) }
-- | Promote a function to a monad, scanning the monadic arguments from
-- left to right. For example,
--
-- > liftM2 (+) [0,1] [0,2] = [0,2,1,3]
-- > liftM2 (+) (Just 1) Nothing = Nothing
--
liftM2 :: (Monad m) => (a1 -> a2 -> r) -> m a1 -> m a2 -> m r
liftM2 f m1 m2 = do { x1 <- m1; x2 <- m2; return (f x1 x2) }
-- | Promote a function to a monad, scanning the monadic arguments from
-- left to right (cf. 'liftM2').
liftM3 :: (Monad m) => (a1 -> a2 -> a3 -> r) -> m a1 -> m a2 -> m a3 -> m r
liftM3 f m1 m2 m3 = do { x1 <- m1; x2 <- m2; x3 <- m3; return (f x1 x2 x3) }
-- | Promote a function to a monad, scanning the monadic arguments from
-- left to right (cf. 'liftM2').
liftM4 :: (Monad m) => (a1 -> a2 -> a3 -> a4 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m r
liftM4 f m1 m2 m3 m4 = do { x1 <- m1; x2 <- m2; x3 <- m3; x4 <- m4; return (f x1 x2 x3 x4) }
-- | Promote a function to a monad, scanning the monadic arguments from
-- left to right (cf. 'liftM2').
liftM5 :: (Monad m) => (a1 -> a2 -> a3 -> a4 -> a5 -> r) -> m a1 -> m a2 -> m a3 -> m a4 -> m a5 -> m r
liftM5 f m1 m2 m3 m4 m5 = do { x1 <- m1; x2 <- m2; x3 <- m3; x4 <- m4; x5 <- m5; return (f x1 x2 x3 x4 x5) }
{-# INLINABLE liftM #-}
{-# SPECIALISE liftM :: (a1->r) -> IO a1 -> IO r #-}
{-# SPECIALISE liftM :: (a1->r) -> Maybe a1 -> Maybe r #-}
{-# INLINABLE liftM2 #-}
{-# SPECIALISE liftM2 :: (a1->a2->r) -> IO a1 -> IO a2 -> IO r #-}
{-# SPECIALISE liftM2 :: (a1->a2->r) -> Maybe a1 -> Maybe a2 -> Maybe r #-}
{-# INLINABLE liftM3 #-}
{-# SPECIALISE liftM3 :: (a1->a2->a3->r) -> IO a1 -> IO a2 -> IO a3 -> IO r #-}
{-# SPECIALISE liftM3 :: (a1->a2->a3->r) -> Maybe a1 -> Maybe a2 -> Maybe a3 -> Maybe r #-}
{-# INLINABLE liftM4 #-}
{-# SPECIALISE liftM4 :: (a1->a2->a3->a4->r) -> IO a1 -> IO a2 -> IO a3 -> IO a4 -> IO r #-}
{-# SPECIALISE liftM4 :: (a1->a2->a3->a4->r) -> Maybe a1 -> Maybe a2 -> Maybe a3 -> Maybe a4 -> Maybe r #-}
{-# INLINABLE liftM5 #-}
{-# SPECIALISE liftM5 :: (a1->a2->a3->a4->a5->r) -> IO a1 -> IO a2 -> IO a3 -> IO a4 -> IO a5 -> IO r #-}
{-# SPECIALISE liftM5 :: (a1->a2->a3->a4->a5->r) -> Maybe a1 -> Maybe a2 -> Maybe a3 -> Maybe a4 -> Maybe a5 -> Maybe r #-}
{- | In many situations, the 'liftM' operations can be replaced by uses of
'ap', which promotes function application.
> return f `ap` x1 `ap` ... `ap` xn
is equivalent to
> liftMn f x1 x2 ... xn
-}
ap :: (Monad m) => m (a -> b) -> m a -> m b
ap m1 m2 = do { x1 <- m1; x2 <- m2; return (x1 x2) }
-- Since many Applicative instances define (<*>) = ap, we
-- cannot define ap = (<*>)
{-# INLINABLE ap #-}
{-# SPECIALISE ap :: IO (a -> b) -> IO a -> IO b #-}
{-# SPECIALISE ap :: Maybe (a -> b) -> Maybe a -> Maybe b #-}
-- instances for Prelude types
-- | @since 2.01
instance Functor ((->) r) where
fmap = (.)
-- | @since 2.01
instance Applicative ((->) a) where
pure = const
(<*>) f g x = f x (g x)
-- | @since 2.01
instance Monad ((->) r) where
f >>= k = \ r -> k (f r) r
-- | @since 2.01
instance Functor ((,) a) where
fmap f (x,y) = (x, f y)
-- | @since 2.01
instance Functor Maybe where
fmap _ Nothing = Nothing
fmap f (Just a) = Just (f a)
-- | @since 2.01
instance Applicative Maybe where
pure = Just
Just f <*> m = fmap f m
Nothing <*> _m = Nothing
Just _m1 *> m2 = m2
Nothing *> _m2 = Nothing
-- | @since 2.01
instance Monad Maybe where
(Just x) >>= k = k x
Nothing >>= _ = Nothing
(>>) = (*>)
fail _ = Nothing
-- -----------------------------------------------------------------------------
-- The Alternative class definition
infixl 3 <|>
-- | A monoid on applicative functors.
--
-- If defined, 'some' and 'many' should be the least solutions
-- of the equations:
--
-- * @some v = (:) '<$>' v '<*>' many v@
--
-- * @many v = some v '<|>' 'pure' []@
class Applicative f => Alternative f where
-- | The identity of '<|>'
empty :: f a
-- | An associative binary operation
(<|>) :: f a -> f a -> f a
-- | One or more.
some :: f a -> f [a]
some v = some_v
where
many_v = some_v <|> pure []
some_v = (fmap (:) v) <*> many_v
-- | Zero or more.
many :: f a -> f [a]
many v = many_v
where
many_v = some_v <|> pure []
some_v = (fmap (:) v) <*> many_v
-- | @since 2.01
instance Alternative Maybe where
empty = Nothing
Nothing <|> r = r
l <|> _ = l
-- -----------------------------------------------------------------------------
-- The MonadPlus class definition
-- | Monads that also support choice and failure.
class (Alternative m, Monad m) => MonadPlus m where
-- | the identity of 'mplus'. It should also satisfy the equations
--
-- > mzero >>= f = mzero
-- > v >> mzero = mzero
--
mzero :: m a
mzero = empty
-- | an associative operation
mplus :: m a -> m a -> m a
mplus = (<|>)
-- | @since 2.01
instance MonadPlus Maybe
----------------------------------------------
-- The list type
-- | @since 2.01
instance Functor [] where
{-# INLINE fmap #-}
fmap = map
-- See Note: [List comprehensions and inlining]
-- | @since 2.01
instance Applicative [] where
{-# INLINE pure #-}
pure x = [x]
{-# INLINE (<*>) #-}
fs <*> xs = [f x | f <- fs, x <- xs]
{-# INLINE (*>) #-}
xs *> ys = [y | _ <- xs, y <- ys]
-- See Note: [List comprehensions and inlining]
-- | @since 2.01
instance Monad [] where
{-# INLINE (>>=) #-}
xs >>= f = [y | x <- xs, y <- f x]
{-# INLINE (>>) #-}
(>>) = (*>)
{-# INLINE fail #-}
fail _ = []
-- | @since 2.01
instance Alternative [] where
empty = []
(<|>) = (++)
-- | @since 2.01
instance MonadPlus []
{-
A few list functions that appear here because they are used here.
The rest of the prelude list functions are in GHC.List.
-}
----------------------------------------------
-- foldr/build/augment
----------------------------------------------
-- | 'foldr', applied to a binary operator, a starting value (typically
-- the right-identity of the operator), and a list, reduces the list
-- using the binary operator, from right to left:
--
-- > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
foldr :: (a -> b -> b) -> b -> [a] -> b
-- foldr _ z [] = z
-- foldr f z (x:xs) = f x (foldr f z xs)
{-# INLINE [0] foldr #-}
-- Inline only in the final stage, after the foldr/cons rule has had a chance
-- Also note that we inline it when it has *two* parameters, which are the
-- ones we are keen about specialising!
foldr k z = go
where
go [] = z
go (y:ys) = y `k` go ys
-- | A list producer that can be fused with 'foldr'.
-- This function is merely
--
-- > build g = g (:) []
--
-- but GHC's simplifier will transform an expression of the form
-- @'foldr' k z ('build' g)@, which may arise after inlining, to @g k z@,
-- which avoids producing an intermediate list.
build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
{-# INLINE [1] build #-}
-- The INLINE is important, even though build is tiny,
-- because it prevents [] getting inlined in the version that
-- appears in the interface file. If [] *is* inlined, it
-- won't match with [] appearing in rules in an importing module.
--
-- The "1" says to inline in phase 1
build g = g (:) []
-- | A list producer that can be fused with 'foldr'.
-- This function is merely
--
-- > augment g xs = g (:) xs
--
-- but GHC's simplifier will transform an expression of the form
-- @'foldr' k z ('augment' g xs)@, which may arise after inlining, to
-- @g k ('foldr' k z xs)@, which avoids producing an intermediate list.
augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
{-# INLINE [1] augment #-}
augment g xs = g (:) xs
{-# RULES
"fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
foldr k z (build g) = g k z
"foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
foldr k z (augment g xs) = g k (foldr k z xs)
"foldr/id" foldr (:) [] = \x -> x
"foldr/app" [1] forall ys. foldr (:) ys = \xs -> xs ++ ys
-- Only activate this from phase 1, because that's
-- when we disable the rule that expands (++) into foldr
-- The foldr/cons rule looks nice, but it can give disastrously
-- bloated code when commpiling
-- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
-- i.e. when there are very very long literal lists
-- So I've disabled it for now. We could have special cases
-- for short lists, I suppose.
-- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
"foldr/single" forall k z x. foldr k z [x] = k x z
"foldr/nil" forall k z. foldr k z [] = z
"foldr/cons/build" forall k z x (g::forall b. (a->b->b) -> b -> b) .
foldr k z (x:build g) = k x (g k z)
"augment/build" forall (g::forall b. (a->b->b) -> b -> b)
(h::forall b. (a->b->b) -> b -> b) .
augment g (build h) = build (\c n -> g c (h c n))
"augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
augment g [] = build g
#-}
-- This rule is true, but not (I think) useful:
-- augment g (augment h t) = augment (\cn -> g c (h c n)) t
----------------------------------------------
-- map
----------------------------------------------
-- | 'map' @f xs@ is the list obtained by applying @f@ to each element
-- of @xs@, i.e.,
--
-- > map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
-- > map f [x1, x2, ...] == [f x1, f x2, ...]
map :: (a -> b) -> [a] -> [b]
{-# NOINLINE [0] map #-}
-- We want the RULEs "map" and "map/coerce" to fire first.
-- map is recursive, so won't inline anyway,
-- but saying so is more explicit, and silences warnings
map _ [] = []
map f (x:xs) = f x : map f xs
-- Note eta expanded
mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
{-# INLINE [0] mapFB #-}
mapFB c f = \x ys -> c (f x) ys
-- The rules for map work like this.
--
-- Up to (but not including) phase 1, we use the "map" rule to
-- rewrite all saturated applications of map with its build/fold
-- form, hoping for fusion to happen.
-- In phase 1 and 0, we switch off that rule, inline build, and
-- switch on the "mapList" rule, which rewrites the foldr/mapFB
-- thing back into plain map.
--
-- It's important that these two rules aren't both active at once
-- (along with build's unfolding) else we'd get an infinite loop
-- in the rules. Hence the activation control below.
--
-- The "mapFB" rule optimises compositions of map.
--
-- This same pattern is followed by many other functions:
-- e.g. append, filter, iterate, repeat, etc.
{-# RULES
"map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
"mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
"mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
#-}
-- See Breitner, Eisenberg, Peyton Jones, and Weirich, "Safe Zero-cost
-- Coercions for Haskell", section 6.5:
-- http://research.microsoft.com/en-us/um/people/simonpj/papers/ext-f/coercible.pdf
{-# RULES "map/coerce" [1] map coerce = coerce #-}
----------------------------------------------
-- append
----------------------------------------------
-- | Append two lists, i.e.,
--
-- > [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
-- > [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
--
-- If the first list is not finite, the result is the first list.
(++) :: [a] -> [a] -> [a]
{-# NOINLINE [1] (++) #-} -- We want the RULE to fire first.
-- It's recursive, so won't inline anyway,
-- but saying so is more explicit
(++) [] ys = ys
(++) (x:xs) ys = x : xs ++ ys
{-# RULES
"++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
#-}
-- |'otherwise' is defined as the value 'True'. It helps to make
-- guards more readable. eg.
--
-- > f x | x < 0 = ...
-- > | otherwise = ...
otherwise :: Bool
otherwise = True
----------------------------------------------
-- Type Char and String
----------------------------------------------
-- | A 'String' is a list of characters. String constants in Haskell are values
-- of type 'String'.
--
type String = [Char]
unsafeChr :: Int -> Char
unsafeChr (I# i#) = C# (chr# i#)
-- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
ord :: Char -> Int
ord (C# c#) = I# (ord# c#)
-- | This 'String' equality predicate is used when desugaring
-- pattern-matches against strings.
eqString :: String -> String -> Bool
eqString [] [] = True
eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
eqString _ _ = False
{-# RULES "eqString" (==) = eqString #-}
-- eqString also has a BuiltInRule in PrelRules.lhs:
-- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2)) = s1==s2
----------------------------------------------
-- 'Int' related definitions
----------------------------------------------
maxInt, minInt :: Int
{- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
#if WORD_SIZE_IN_BITS == 31
minInt = I# (-0x40000000#)
maxInt = I# 0x3FFFFFFF#
#elif WORD_SIZE_IN_BITS == 32
minInt = I# (-0x80000000#)
maxInt = I# 0x7FFFFFFF#
#else
minInt = I# (-0x8000000000000000#)
maxInt = I# 0x7FFFFFFFFFFFFFFF#
#endif
----------------------------------------------
-- The function type
----------------------------------------------
-- | Identity function.
id :: a -> a
id x = x
-- Assertion function. This simply ignores its boolean argument.
-- The compiler may rewrite it to @('assertError' line)@.
-- | 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.
-- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
-- but from Template Haskell onwards it's simply
-- defined here in Base.lhs
assert :: Bool -> a -> a
assert _pred r = r
breakpoint :: a -> a
breakpoint r = r
breakpointCond :: Bool -> a -> a
breakpointCond _ r = r
data Opaque = forall a. O a
-- | @const x@ is a unary function which evaluates to @x@ for all inputs.
--
-- For instance,
--
-- >>> map (const 42) [0..3]
-- [42,42,42,42]
const :: a -> b -> a
const x _ = x
-- | Function composition.
{-# INLINE (.) #-}
-- Make sure it has TWO args only on the left, so that it inlines
-- when applied to two functions, even if there is no final argument
(.) :: (b -> c) -> (a -> b) -> a -> c
(.) f g = \x -> f (g x)
-- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
flip :: (a -> b -> c) -> b -> a -> c
flip f x y = f y x
-- | Application operator. This operator is redundant, since ordinary
-- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
-- low, right-associative binding precedence, so it sometimes allows
-- parentheses to be omitted; for example:
--
-- > f $ g $ h x = f (g (h x))
--
-- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
-- or @'Data.List.zipWith' ('$') fs xs@.
{-# INLINE ($) #-}
($) :: (a -> b) -> a -> b
f $ x = f x
-- | Strict (call-by-value) application operator. It takes a function and an
-- argument, evaluates the argument to weak head normal form (WHNF), then calls
-- the function with that value.
($!) :: (a -> b) -> a -> b
f $! x = let !vx = x in f vx -- see #2273
-- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
until :: (a -> Bool) -> (a -> a) -> a -> a
until p f = go
where
go x | p x = x
| otherwise = go (f x)
-- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
-- used as an infix operator, and its typing forces its first argument
-- (which is usually overloaded) to have the same type as the second.
asTypeOf :: a -> a -> a
asTypeOf = const
----------------------------------------------
-- Functor/Applicative/Monad instances for IO
----------------------------------------------
-- | @since 2.01
instance Functor IO where
fmap f x = x >>= (pure . f)
-- | @since 2.01
instance Applicative IO where
{-# INLINE pure #-}
{-# INLINE (*>) #-}
pure = returnIO
(*>) = thenIO
(<*>) = ap
-- | @since 2.01
instance Monad IO where
{-# INLINE (>>) #-}
{-# INLINE (>>=) #-}
(>>) = (*>)
(>>=) = bindIO
fail s = failIO s
-- | @since 4.9.0.0
instance Alternative IO where
empty = failIO "mzero"
(<|>) = mplusIO
-- | @since 4.9.0.0
instance MonadPlus IO
returnIO :: a -> IO a
returnIO x = IO (\ s -> (# s, x #))
bindIO :: IO a -> (a -> IO b) -> IO b
bindIO (IO m) k = IO (\ s -> case m s of (# new_s, a #) -> unIO (k a) new_s)
thenIO :: IO a -> IO b -> IO b
thenIO (IO m) k = IO (\ s -> case m s of (# new_s, _ #) -> unIO k new_s)
unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
unIO (IO a) = a
{- |
Returns the 'tag' of a constructor application; this function is used
by the deriving code for Eq, Ord and Enum.
The primitive dataToTag# requires an evaluated constructor application
as its argument, so we provide getTag as a wrapper that performs the
evaluation before calling dataToTag#. We could have dataToTag#
evaluate its argument, but we prefer to do it this way because (a)
dataToTag# can be an inline primop if it doesn't need to do any
evaluation, and (b) we want to expose the evaluation to the
simplifier, because it might be possible to eliminate the evaluation
in the case when the argument is already known to be evaluated.
-}
{-# INLINE getTag #-}
getTag :: a -> Int#
getTag !x = dataToTag# x
----------------------------------------------
-- Numeric primops
----------------------------------------------
-- Definitions of the boxed PrimOps; these will be
-- used in the case of partial applications, etc.
{-# INLINE quotInt #-}
{-# INLINE remInt #-}
quotInt, remInt, divInt, modInt :: Int -> Int -> Int
(I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
(I# x) `remInt` (I# y) = I# (x `remInt#` y)
(I# x) `divInt` (I# y) = I# (x `divInt#` y)
(I# x) `modInt` (I# y) = I# (x `modInt#` y)
quotRemInt :: Int -> Int -> (Int, Int)
(I# x) `quotRemInt` (I# y) = case x `quotRemInt#` y of
(# q, r #) ->
(I# q, I# r)
divModInt :: Int -> Int -> (Int, Int)
(I# x) `divModInt` (I# y) = case x `divModInt#` y of
(# q, r #) -> (I# q, I# r)
divModInt# :: Int# -> Int# -> (# Int#, Int# #)
x# `divModInt#` y#
| isTrue# (x# ># 0#) && isTrue# (y# <# 0#) =
case (x# -# 1#) `quotRemInt#` y# of
(# q, r #) -> (# q -# 1#, r +# y# +# 1# #)
| isTrue# (x# <# 0#) && isTrue# (y# ># 0#) =
case (x# +# 1#) `quotRemInt#` y# of
(# q, r #) -> (# q -# 1#, r +# y# -# 1# #)
| otherwise =
x# `quotRemInt#` y#
-- Wrappers for the shift operations. The uncheckedShift# family are
-- undefined when the amount being shifted by is greater than the size
-- in bits of Int#, so these wrappers perform a check and return
-- either zero or -1 appropriately.
--
-- Note that these wrappers still produce undefined results when the
-- second argument (the shift amount) is negative.
-- | Shift the argument left by the specified number of bits
-- (which must be non-negative).
shiftL# :: Word# -> Int# -> Word#
a `shiftL#` b | isTrue# (b >=# WORD_SIZE_IN_BITS#) = 0##
| otherwise = a `uncheckedShiftL#` b
-- | Shift the argument right by the specified number of bits
-- (which must be non-negative).
-- The "RL" means "right, logical" (as opposed to RA for arithmetic)
-- (although an arithmetic right shift wouldn't make sense for Word#)
shiftRL# :: Word# -> Int# -> Word#
a `shiftRL#` b | isTrue# (b >=# WORD_SIZE_IN_BITS#) = 0##
| otherwise = a `uncheckedShiftRL#` b
-- | Shift the argument left by the specified number of bits
-- (which must be non-negative).
iShiftL# :: Int# -> Int# -> Int#
a `iShiftL#` b | isTrue# (b >=# WORD_SIZE_IN_BITS#) = 0#
| otherwise = a `uncheckedIShiftL#` b
-- | Shift the argument right (signed) by the specified number of bits
-- (which must be non-negative).
-- The "RA" means "right, arithmetic" (as opposed to RL for logical)
iShiftRA# :: Int# -> Int# -> Int#
a `iShiftRA#` b | isTrue# (b >=# WORD_SIZE_IN_BITS#) = if isTrue# (a <# 0#)
then (-1#)
else 0#
| otherwise = a `uncheckedIShiftRA#` b
-- | Shift the argument right (unsigned) by the specified number of bits
-- (which must be non-negative).
-- The "RL" means "right, logical" (as opposed to RA for arithmetic)
iShiftRL# :: Int# -> Int# -> Int#
a `iShiftRL#` b | isTrue# (b >=# WORD_SIZE_IN_BITS#) = 0#
| otherwise = a `uncheckedIShiftRL#` b
-- Rules for C strings (the functions themselves are now in GHC.CString)
{-# RULES
"unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
"unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
"unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
-- There's a built-in rule (in PrelRules.lhs) for
-- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
#-}