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
+ 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.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
+GHC.Base Classes: Eq, Ord, Functor, Monad
+ Types: list, (), Int, Bool, Ordering, Char, String
-Data.Tuple Types: tuples, plus instances for GHC.Base classes
+Data.Tuple Types: tuples, plus instances for GHC.Base classes
-GHC.Show Class: Show, plus instances for GHC.Base/GHC.Tup types
+GHC.Show Class: Show, plus instances for GHC.Base/GHC.Tup types
-GHC.Enum Class: Enum, 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
+Data.Maybe Type: Maybe, plus instances for GHC.Base classes
-GHC.List List functions
+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)
+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
+ 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 intances for classes so far
+GHC.Real Classes: Real, Integral, Fractional, RealFrac
+ plus instances for Int, Integer
+ Types: Ratio, Rational
+ plus intances for classes so far
- Rational is needed here because it is mentioned in the signature
- of 'toRational' in class Real
+ 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
+GHC.ST The ST monad, instances and a few helper functions
-Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
+Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
-GHC.Arr Types: Array, MutableArray, MutableVar
+GHC.Arr Types: Array, MutableArray, MutableVar
- Arrays are used by a function in GHC.Float
+ Arrays are used by a function in GHC.Float
-GHC.Float Classes: Floating, RealFloat
- Types: Float, Double, plus instances of all classes so far
+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
+ 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.
-- #hide
module GHC.Base
- (
- module GHC.Base,
- module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
- module GHC.Err -- of people having to import it explicitly
+ (
+ module GHC.Base,
+ module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
+ module GHC.Err -- of people having to import it explicitly
)
- where
+ where
import GHC.Prim
import {-# SOURCE #-} GHC.Err
infixl 1 >>, >>=
infixr 0 $
-default () -- Double isn't available yet
+default () -- Double isn't available yet
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{DEBUGGING STUFF}
%* (for use when compiling GHC.Base itself doesn't work)
-%* *
+%* *
%*********************************************************
\begin{code}
%*********************************************************
-%* *
+%* *
\subsection{Standard classes @Eq@, @Ord@}
-%* *
+%* *
%*********************************************************
\begin{code}
-- Minimal complete definition: either '==' or '/='.
--
class Eq a where
- (==), (/=) :: a -> a -> Bool
+ (==), (/=) :: a -> a -> Bool
- x /= y = not (x == y)
- x == y = not (x /= y)
+ x /= y = not (x == y)
+ x == y = not (x /= y)
-- | The 'Ord' class is used for totally ordered datatypes.
--
-- Using 'compare' can be more efficient for complex types.
--
class (Eq a) => Ord a where
- compare :: a -> a -> Ordering
+ compare :: a -> a -> Ordering
(<), (<=), (>), (>=) :: a -> a -> Bool
- max, min :: a -> a -> a
+ max, min :: a -> a -> a
compare x y
- | x == y = EQ
- | x <= y = LT -- NB: must be '<=' not '<' to validate the
- -- above claim about the minimal things that
- -- can be defined for an instance of Ord
- | otherwise = GT
+ | x == y = EQ
+ | x <= y = LT -- NB: must be '<=' not '<' to validate the
+ -- above claim about the minimal things that
+ -- can be defined for an instance of Ord
+ | otherwise = GT
- x < y = case compare x y of { LT -> True; _other -> False }
+ x < y = case compare x y of { LT -> True; _other -> False }
x <= y = case compare x y of { GT -> False; _other -> True }
- x > y = case compare x y of { GT -> True; _other -> False }
+ x > y = case compare x y of { GT -> True; _other -> False }
x >= y = case compare x y of { LT -> False; _other -> True }
- -- These two default methods use '<=' rather than 'compare'
- -- because the latter is often more expensive
+ -- These two default methods use '<=' rather than 'compare'
+ -- because the latter is often more expensive
max x y = if x <= y then y else x
min x y = if x <= y then x else y
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Monadic classes @Functor@, @Monad@ }
-%* *
+%* *
%*********************************************************
\begin{code}
-- by the first, like sequencing operators (such as the semicolon)
-- in imperative languages.
(>>) :: forall a b. m a -> m b -> m b
- -- Explicit for-alls so that we know what order to
- -- give type arguments when desugaring
+ -- Explicit for-alls so that we know what order to
+ -- give type arguments when desugaring
-- | Inject a value into the monadic type.
return :: a -> m a
-- | 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.
- fail :: String -> m a
+ fail :: String -> m a
m >> k = m >>= \_ -> k
fail s = error s
%*********************************************************
-%* *
+%* *
\subsection{The list type}
-%* *
+%* *
%*********************************************************
\begin{code}
data [] a = [] | a : [a] -- do explicitly: deriving (Eq, Ord)
- -- to avoid weird names like con2tag_[]#
+ -- to avoid weird names like con2tag_[]#
instance (Eq a) => Eq [a] where
m >>= k = foldr ((++) . k) [] m
m >> k = foldr ((++) . (\ _ -> k)) [] m
return x = [x]
- fail _ = []
+ fail _ = []
\end{code}
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/build/augment
----------------------------------------------
\begin{code}
{-# INLINE [0] foldr #-}
-- Inline only in the final stage, after the foldr/cons rule has had a chance
foldr k z xs = go xs
- where
- go [] = z
- go (y:ys) = y `k` go ys
+ 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 (:) []
+-- > 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]
+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
+ -- 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
+-- > 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
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
+"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 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
+"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... ]
+-- 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/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/single" forall k z x. foldr k z [x] = k x z
+"foldr/nil" forall k z. foldr k z [] = 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))
+ (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
+ 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
+-- augment g (augment h t) = augment (\cn -> g c (h c n)) t
\end{code}
----------------------------------------------
--- map
+-- map
----------------------------------------------
\begin{code}
-- 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)
+"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)
#-}
\end{code}
----------------------------------------------
--- append
+-- append
----------------------------------------------
\begin{code}
-- | Append two lists, i.e.,
(++) (x:xs) ys = x : xs ++ ys
{-# RULES
-"++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
+"++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
#-}
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Bool@}
-%* *
+%* *
%*********************************************************
\begin{code}
-- 'Prelude.fromEnum' 'False' the value zero, and
-- 'Prelude.fromEnum' 'True' the value 1.
data Bool = False | True deriving (Eq, Ord)
- -- Read in GHC.Read, Show in GHC.Show
+ -- Read in GHC.Read, Show in GHC.Show
-- Boolean functions
-- | Boolean \"and\"
-(&&) :: Bool -> Bool -> Bool
-True && x = x
-False && _ = False
+(&&) :: Bool -> Bool -> Bool
+True && x = x
+False && _ = False
-- | Boolean \"or\"
-(||) :: Bool -> Bool -> Bool
-True || _ = True
-False || x = x
+(||) :: Bool -> Bool -> Bool
+True || _ = True
+False || x = x
-- | Boolean \"not\"
-not :: Bool -> Bool
-not True = False
-not False = True
+not :: Bool -> Bool
+not True = False
+not False = True
-- |'otherwise' is defined as the value 'True'. It helps to make
-- guards more readable. eg.
--
-- > f x | x < 0 = ...
-- > | otherwise = ...
-otherwise :: Bool
-otherwise = True
+otherwise :: Bool
+otherwise = True
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{The @()@ type}
-%* *
+%* *
%*********************************************************
The Unit type is here because virtually any program needs it (whereas
%*********************************************************
-%* *
+%* *
\subsection{Type @Ordering@}
-%* *
+%* *
%*********************************************************
\begin{code}
-- than, equal to, or greater than. An 'Ordering' is returned by
-- 'compare'.
data Ordering = LT | EQ | GT deriving (Eq, Ord)
- -- Read in GHC.Read, Show in GHC.Show
+ -- Read in GHC.Read, Show in GHC.Show
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Char@ and @String@}
-%* *
+%* *
%*********************************************************
\begin{code}
\begin{code}
eqString :: String -> String -> Bool
-eqString [] [] = True
+eqString [] [] = True
eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
-eqString cs1 cs2 = False
+eqString cs1 cs2 = False
{-# RULES "eqString" (==) = eqString #-}
-- eqString also has a BuiltInRule in PrelRules.lhs:
--- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
+-- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Type @Int@}
-%* *
+%* *
%*********************************************************
\begin{code}
%*********************************************************
-%* *
+%* *
\subsection{The function type}
-%* *
+%* *
%*********************************************************
\begin{code}
-- | Identity function.
-id :: a -> a
-id x = x
+id :: a -> a
+id x = x
-- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
-- magical strictness property: it is lazy in its first argument,
-- 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
+-- 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
data Opaque = forall a. O a
-- | Constant function.
-const :: a -> b -> a
-const x _ = x
+const :: a -> b -> a
+const x _ = x
-- | Function composition.
{-# INLINE (.) #-}
-(.) :: (b -> c) -> (a -> b) -> a -> c
-(.) f g x = f (g x)
+(.) :: (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
+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
-- 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
+($) :: (a -> b) -> a -> b
+f $ x = f x
-- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
-until :: (a -> Bool) -> (a -> a) -> a -> a
-until p f x | p x = x
- | otherwise = until p f (f x)
+until :: (a -> Bool) -> (a -> a) -> a -> a
+until p f x | p x = x
+ | otherwise = until p f (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
+asTypeOf :: a -> a -> a
+asTypeOf = const
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Generics}
-%* *
+%* *
%*********************************************************
\begin{code}
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{@getTag@}
-%* *
+%* *
%*********************************************************
Returns the 'tag' of a constructor application; this function is used
\end{code}
%*********************************************************
-%* *
+%* *
\subsection{Numeric primops}
-%* *
+%* *
%*********************************************************
\begin{code}
divInt# :: Int# -> Int# -> Int#
x# `divInt#` y#
- -- Be careful NOT to overflow if we do any additional arithmetic
- -- on the arguments... the following previous version of this
- -- code has problems with overflow:
+ -- Be careful NOT to overflow if we do any additional arithmetic
+ -- on the arguments... the following previous version of this
+ -- code has problems with overflow:
-- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
-- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
| (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
-- (which must be non-negative).
shiftL# :: Word# -> Int# -> Word#
a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
- | otherwise = a `uncheckedShiftL#` b
+ | otherwise = a `uncheckedShiftL#` b
-- | Shift the argument right by the specified number of bits
-- (which must be non-negative).
shiftRL# :: Word# -> Int# -> Word#
a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
- | otherwise = a `uncheckedShiftRL#` b
+ | 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 | b >=# WORD_SIZE_IN_BITS# = 0#
- | otherwise = a `uncheckedIShiftL#` b
+ | otherwise = a `uncheckedIShiftL#` b
-- | Shift the argument right (signed) by the specified number of bits
-- (which must be non-negative).
iShiftRA# :: Int# -> Int# -> Int#
a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
- | otherwise = a `uncheckedIShiftRA#` b
+ | otherwise = a `uncheckedIShiftRA#` b
-- | Shift the argument right (unsigned) by the specified number of bits
-- (which must be non-negative).
iShiftRL# :: Int# -> Int# -> Int#
a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
- | otherwise = a `uncheckedIShiftRL#` b
+ | otherwise = a `uncheckedIShiftRL#` b
#if WORD_SIZE_IN_BITS == 32
{-# RULES
%********************************************************
-%* *
+%* *
\subsection{Unpacking C strings}
-%* *
+%* *
%********************************************************
This code is needed for virtually all programs, since it's used for
where
unpack nh
| ch `eqChar#` '\0'# = []
- | otherwise = C# ch : unpack (nh +# 1#)
+ | otherwise = C# ch : unpack (nh +# 1#)
where
- ch = indexCharOffAddr# addr nh
+ ch = indexCharOffAddr# addr nh
unpackAppendCString# :: Addr# -> [Char] -> [Char]
unpackAppendCString# addr rest
where
unpack nh
| ch `eqChar#` '\0'# = rest
- | otherwise = C# ch : unpack (nh +# 1#)
+ | otherwise = C# ch : unpack (nh +# 1#)
where
- ch = indexCharOffAddr# addr nh
+ ch = indexCharOffAddr# addr nh
unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
{-# NOINLINE [0] unpackFoldrCString# #-}
-- Don't inline till right at the end;
-- usually the unpack-list rule turns it into unpackCStringList
-- It also has a BuiltInRule in PrelRules.lhs:
--- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
--- = unpackFoldrCString# "foobaz" c n
+-- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
+-- = unpackFoldrCString# "foobaz" c n
unpackFoldrCString# addr f z
= unpack 0#
where
unpack nh
| ch `eqChar#` '\0'# = z
- | otherwise = C# ch `f` unpack (nh +# 1#)
+ | otherwise = C# ch `f` unpack (nh +# 1#)
where
- ch = indexCharOffAddr# addr nh
+ ch = indexCharOffAddr# addr nh
unpackCStringUtf8# :: Addr# -> [Char]
unpackCStringUtf8# addr
(ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
unpack (nh +# 4#)
where
- ch = indexCharOffAddr# addr nh
+ ch = indexCharOffAddr# addr nh
unpackNBytes# :: Addr# -> Int# -> [Char]
unpackNBytes# _addr 0# = []
unpack acc i#
| i# <# 0# = acc
| otherwise =
- case indexCharOffAddr# addr i# of
- ch -> unpack (C# ch : acc) (i# -# 1#)
+ case indexCharOffAddr# addr i# of
+ ch -> unpack (C# ch : acc) (i# -# 1#)
{-# RULES
-"unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
+"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
+-- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
#-}
\end{code}
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