1 % -----------------------------------------------------------------------------
2 % $Id: PrelBase.lhs,v 1.52 2001/09/26 15:12:37 simonpj Exp $
4 % (c) The University of Glasgow, 1992-2000
6 \section[PrelBase]{Module @PrelBase@}
9 The overall structure of the GHC Prelude is a bit tricky.
11 a) We want to avoid "orphan modules", i.e. ones with instance
12 decls that don't belong either to a tycon or a class
13 defined in the same module
15 b) We want to avoid giant modules
17 So the rough structure is as follows, in (linearised) dependency order
20 PrelGHC Has no implementation. It defines built-in things, and
21 by importing it you bring them into scope.
22 The source file is PrelGHC.hi-boot, which is just
23 copied to make PrelGHC.hi
25 Classes: CCallable, CReturnable
27 PrelBase Classes: Eq, Ord, Functor, Monad
28 Types: list, (), Int, Bool, Ordering, Char, String
30 PrelTup Types: tuples, plus instances for PrelBase classes
32 PrelShow Class: Show, plus instances for PrelBase/PrelTup types
34 PrelEnum Class: Enum, plus instances for PrelBase/PrelTup types
36 PrelMaybe Type: Maybe, plus instances for PrelBase classes
38 PrelNum Class: Num, plus instances for Int
39 Type: Integer, plus instances for all classes so far (Eq, Ord, Num, Show)
41 Integer is needed here because it is mentioned in the signature
42 of 'fromInteger' in class Num
44 PrelReal Classes: Real, Integral, Fractional, RealFrac
45 plus instances for Int, Integer
46 Types: Ratio, Rational
47 plus intances for classes so far
49 Rational is needed here because it is mentioned in the signature
50 of 'toRational' in class Real
52 Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
54 PrelArr Types: Array, MutableArray, MutableVar
56 Does *not* contain any ByteArray stuff (see PrelByteArr)
57 Arrays are used by a function in PrelFloat
59 PrelFloat Classes: Floating, RealFloat
60 Types: Float, Double, plus instances of all classes so far
62 This module contains everything to do with floating point.
63 It is a big module (900 lines)
64 With a bit of luck, many modules can be compiled without ever reading PrelFloat.hi
66 PrelByteArr Types: ByteArray, MutableByteArray
68 We want this one to be after PrelFloat, because it defines arrays
72 Other Prelude modules are much easier with fewer complex dependencies.
76 {-# OPTIONS -fno-implicit-prelude #-}
83 module PrelGHC, -- Re-export PrelGHC and PrelErr, to avoid lots
84 module PrelErr -- of people having to import it explicitly
89 import {-# SOURCE #-} PrelErr
93 infix 4 ==, /=, <, <=, >=, >
99 default () -- Double isn't available yet
103 %*********************************************************
105 \subsection{DEBUGGING STUFF}
106 %* (for use when compiling PrelBase itself doesn't work)
108 %*********************************************************
112 data Bool = False | True
113 data Ordering = LT | EQ | GT
121 (&&) True True = True
127 unpackCString# :: Addr# -> [Char]
128 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
129 unpackAppendCString# :: Addr# -> [Char] -> [Char]
130 unpackCStringUtf8# :: Addr# -> [Char]
131 unpackCString# a = error "urk"
132 unpackFoldrCString# a = error "urk"
133 unpackAppendCString# a = error "urk"
134 unpackCStringUtf8# a = error "urk"
139 %*********************************************************
141 \subsection{Standard classes @Eq@, @Ord@}
143 %*********************************************************
147 (==), (/=) :: a -> a -> Bool
149 x /= y = not (x == y)
150 x == y = not (x /= y)
152 class (Eq a) => Ord a where
153 compare :: a -> a -> Ordering
154 (<), (<=), (>), (>=) :: a -> a -> Bool
155 max, min :: a -> a -> a
157 -- An instance of Ord should define either 'compare' or '<='.
158 -- Using 'compare' can be more efficient for complex types.
162 | x <= y = LT -- NB: must be '<=' not '<' to validate the
163 -- above claim about the minimal things that
164 -- can be defined for an instance of Ord
167 x < y = case compare x y of { LT -> True; _other -> False }
168 x <= y = case compare x y of { GT -> False; _other -> True }
169 x > y = case compare x y of { GT -> True; _other -> False }
170 x >= y = case compare x y of { LT -> False; _other -> True }
172 -- These two default methods use '<=' rather than 'compare'
173 -- because the latter is often more expensive
174 max x y = if x <= y then y else x
175 min x y = if x <= y then x else y
178 %*********************************************************
180 \subsection{Monadic classes @Functor@, @Monad@ }
182 %*********************************************************
185 class Functor f where
186 fmap :: (a -> b) -> f a -> f b
189 (>>=) :: m a -> (a -> m b) -> m b
190 (>>) :: m a -> m b -> m b
192 fail :: String -> m a
194 m >> k = m >>= \_ -> k
199 %*********************************************************
201 \subsection{The list type}
203 %*********************************************************
206 data [] a = [] | a : [a] -- do explicitly: deriving (Eq, Ord)
207 -- to avoid weird names like con2tag_[]#
210 instance (Eq a) => Eq [a] where
211 {-# SPECIALISE instance Eq [Char] #-}
213 (x:xs) == (y:ys) = x == y && xs == ys
216 instance (Ord a) => Ord [a] where
217 {-# SPECIALISE instance Ord [Char] #-}
219 compare [] (_:_) = LT
220 compare (_:_) [] = GT
221 compare (x:xs) (y:ys) = case compare x y of
225 instance Functor [] where
228 instance Monad [] where
229 m >>= k = foldr ((++) . k) [] m
230 m >> k = foldr ((++) . (\ _ -> k)) [] m
235 A few list functions that appear here because they are used here.
236 The rest of the prelude list functions are in PrelList.
238 ----------------------------------------------
239 -- foldr/build/augment
240 ----------------------------------------------
243 foldr :: (a -> b -> b) -> b -> [a] -> b
245 -- foldr f z (x:xs) = f x (foldr f z xs)
246 {-# INLINE [0] foldr #-}
247 -- Inline only in the final stage, after the foldr/cons rule has had a chance
251 go (y:ys) = y `k` go ys
253 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
254 {-# INLINE [1] build #-}
255 -- The INLINE is important, even though build is tiny,
256 -- because it prevents [] getting inlined in the version that
257 -- appears in the interface file. If [] *is* inlined, it
258 -- won't match with [] appearing in rules in an importing module.
260 -- The "1" says to inline in phase 1
264 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
265 {-# INLINE [1] augment #-}
266 augment g xs = g (:) xs
269 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
270 foldr k z (build g) = g k z
272 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
273 foldr k z (augment g xs) = g k (foldr k z xs)
275 "foldr/id" foldr (:) [] = \x->x
276 "foldr/app" forall xs ys. foldr (:) ys xs = append xs ys
278 "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
279 "foldr/nil" forall k z. foldr k z [] = z
281 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
282 (h::forall b. (a->b->b) -> b -> b) .
283 augment g (build h) = build (\c n -> g c (h c n))
284 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
285 augment g [] = build g
288 -- This rule is true, but not (I think) useful:
289 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
293 ----------------------------------------------
295 ----------------------------------------------
298 map :: (a -> b) -> [a] -> [b]
299 {-# NOINLINE [1] map #-}
303 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
304 mapFB c f x ys = c (f x) ys
306 mapList :: (a -> b) -> [a] -> [b]
308 mapList f (x:xs) = f x : mapList f xs
311 "map" forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
312 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
313 "mapList" forall f. foldr (mapFB (:) f) [] = mapList f
318 ----------------------------------------------
320 ----------------------------------------------
322 (++) :: [a] -> [a] -> [a]
323 {-# NOINLINE [1] (++) #-}
327 "++" forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
330 append :: [a] -> [a] -> [a]
332 append (x:xs) ys = x : append xs ys
336 %*********************************************************
338 \subsection{Type @Bool@}
340 %*********************************************************
343 data Bool = False | True deriving (Eq, Ord)
344 -- Read in PrelRead, Show in PrelShow
348 (&&), (||) :: Bool -> Bool -> Bool
363 %*********************************************************
365 \subsection{The @()@ type}
367 %*********************************************************
369 The Unit type is here because virtually any program needs it (whereas
370 some programs may get away without consulting PrelTup). Furthermore,
371 the renamer currently *always* asks for () to be in scope, so that
372 ccalls can use () as their default type; so when compiling PrelBase we
373 need (). (We could arrange suck in () only if -fglasgow-exts, but putting
374 it here seems more direct.)
383 instance Ord () where
394 %*********************************************************
396 \subsection{Type @Ordering@}
398 %*********************************************************
401 data Ordering = LT | EQ | GT deriving (Eq, Ord)
402 -- Read in PrelRead, Show in PrelShow
406 %*********************************************************
408 \subsection{Type @Char@ and @String@}
410 %*********************************************************
417 -- We don't use deriving for Eq and Ord, because for Ord the derived
418 -- instance defines only compare, which takes two primops. Then
419 -- '>' uses compare, and therefore takes two primops instead of one.
421 instance Eq Char where
422 (C# c1) == (C# c2) = c1 `eqChar#` c2
423 (C# c1) /= (C# c2) = c1 `neChar#` c2
425 instance Ord Char where
426 (C# c1) > (C# c2) = c1 `gtChar#` c2
427 (C# c1) >= (C# c2) = c1 `geChar#` c2
428 (C# c1) <= (C# c2) = c1 `leChar#` c2
429 (C# c1) < (C# c2) = c1 `ltChar#` c2
432 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
433 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
434 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
435 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
436 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
437 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
441 chr (I# i#) | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
442 | otherwise = error "Prelude.chr: bad argument"
444 unsafeChr :: Int -> Char
445 unsafeChr (I# i#) = C# (chr# i#)
448 ord (C# c#) = I# (ord# c#)
451 String equality is used when desugaring pattern-matches against strings.
454 eqString :: String -> String -> Bool
457 {-# RULES "eqString" (==) = eqString #-}
460 %*********************************************************
462 \subsection{Type @Int@}
464 %*********************************************************
469 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
474 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
475 #if WORD_SIZE_IN_BITS == 31
476 minInt = I# (-0x40000000#)
477 maxInt = I# 0x3FFFFFFF#
478 #elif WORD_SIZE_IN_BITS == 32
479 minInt = I# (-0x80000000#)
480 maxInt = I# 0x7FFFFFFF#
482 minInt = I# (-0x8000000000000000#)
483 maxInt = I# 0x7FFFFFFFFFFFFFFF#
486 instance Eq Int where
490 instance Ord Int where
497 compareInt :: Int -> Int -> Ordering
498 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
500 compareInt# :: Int# -> Int# -> Ordering
508 %*********************************************************
510 \subsection{The function type}
512 %*********************************************************
523 -- function composition
525 (.) :: (b -> c) -> (a -> b) -> a -> c
528 -- flip f takes its (first) two arguments in the reverse order of f.
529 flip :: (a -> b -> c) -> b -> a -> c
532 -- right-associating infix application operator (useful in continuation-
535 ($) :: (a -> b) -> a -> b
538 -- until p f yields the result of applying f until p holds.
539 until :: (a -> Bool) -> (a -> a) -> a -> a
540 until p f x | p x = x
541 | otherwise = until p f (f x)
543 -- asTypeOf is a type-restricted version of const. It is usually used
544 -- as an infix operator, and its typing forces its first argument
545 -- (which is usually overloaded) to have the same type as the second.
546 asTypeOf :: a -> a -> a
550 %*********************************************************
552 \subsection{CCallable instances}
554 %*********************************************************
556 Defined here to avoid orphans
559 instance CCallable Char
560 instance CReturnable Char
562 instance CCallable Int
563 instance CReturnable Int
565 instance CReturnable () -- Why, exactly?
569 %*********************************************************
571 \subsection{Generics}
573 %*********************************************************
577 data a :+: b = Inl a | Inr b
578 data a :*: b = a :*: b
582 %*********************************************************
584 \subsection{Numeric primops}
586 %*********************************************************
589 divInt#, modInt# :: Int# -> Int# -> Int#
591 | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
592 | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
593 | otherwise = x# `quotInt#` y#
595 | (x# ># 0#) && (y# <# 0#) ||
596 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
602 Definitions of the boxed PrimOps; these will be
603 used in the case of partial applications, etc.
612 {-# INLINE plusInt #-}
613 {-# INLINE minusInt #-}
614 {-# INLINE timesInt #-}
615 {-# INLINE quotInt #-}
616 {-# INLINE remInt #-}
617 {-# INLINE negateInt #-}
619 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
620 (I# x) `plusInt` (I# y) = I# (x +# y)
621 (I# x) `minusInt` (I# y) = I# (x -# y)
622 (I# x) `timesInt` (I# y) = I# (x *# y)
623 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
624 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
625 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
626 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
629 "x# +# 0#" forall x#. x# +# 0# = x#
630 "0# +# x#" forall x#. 0# +# x# = x#
631 "x# -# 0#" forall x#. x# -# 0# = x#
632 "x# -# x#" forall x#. x# -# x# = 0#
633 "x# *# 0#" forall x#. x# *# 0# = 0#
634 "0# *# x#" forall x#. 0# *# x# = 0#
635 "x# *# 1#" forall x#. x# *# 1# = x#
636 "1# *# x#" forall x#. 1# *# x# = x#
639 gcdInt (I# a) (I# b) = g a b
640 where g 0# 0# = error "PrelBase.gcdInt: gcd 0 0 is undefined"
643 g _ _ = I# (gcdInt# absA absB)
645 absInt x = if x <# 0# then negateInt# x else x
650 negateInt :: Int -> Int
651 negateInt (I# x) = I# (negateInt# x)
653 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
654 (I# x) `gtInt` (I# y) = x ># y
655 (I# x) `geInt` (I# y) = x >=# y
656 (I# x) `eqInt` (I# y) = x ==# y
657 (I# x) `neInt` (I# y) = x /=# y
658 (I# x) `ltInt` (I# y) = x <# y
659 (I# x) `leInt` (I# y) = x <=# y
662 "x# ># x#" forall x#. x# ># x# = False
663 "x# >=# x#" forall x#. x# >=# x# = True
664 "x# ==# x#" forall x#. x# ==# x# = True
665 "x# /=# x#" forall x#. x# /=# x# = False
666 "x# <# x#" forall x#. x# <# x# = False
667 "x# <=# x#" forall x#. x# <=# x# = True
670 #if WORD_SIZE_IN_BITS == 32
672 "narrow32Int#" forall x#. narrow32Int# x# = x#
673 "narrow32Word#" forall x#. narrow32Word# x# = x#
678 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
679 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
684 %********************************************************
686 \subsection{Unpacking C strings}
688 %********************************************************
690 This code is needed for virtually all programs, since it's used for
691 unpacking the strings of error messages.
694 unpackCString# :: Addr# -> [Char]
695 {-# NOINLINE [1] unpackCString# #-}
696 unpackCString# a = unpackCStringList# a
698 unpackCStringList# :: Addr# -> [Char]
699 unpackCStringList# addr
703 | ch `eqChar#` '\0'# = []
704 | otherwise = C# ch : unpack (nh +# 1#)
706 ch = indexCharOffAddr# addr nh
708 unpackAppendCString# :: Addr# -> [Char] -> [Char]
709 unpackAppendCString# addr rest
713 | ch `eqChar#` '\0'# = rest
714 | otherwise = C# ch : unpack (nh +# 1#)
716 ch = indexCharOffAddr# addr nh
718 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
719 {-# NOINLINE [0] unpackFoldrCString# #-}
720 -- Don't inline till right at the end;
721 -- usually the unpack-list rule turns it into unpackCStringList
722 unpackFoldrCString# addr f z
726 | ch `eqChar#` '\0'# = z
727 | otherwise = C# ch `f` unpack (nh +# 1#)
729 ch = indexCharOffAddr# addr nh
731 unpackCStringUtf8# :: Addr# -> [Char]
732 unpackCStringUtf8# addr
736 | ch `eqChar#` '\0'# = []
737 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
738 | ch `leChar#` '\xDF'# =
739 C# (chr# ((ord# ch -# 0xC0#) `iShiftL#` 6# +#
740 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
742 | ch `leChar#` '\xEF'# =
743 C# (chr# ((ord# ch -# 0xE0#) `iShiftL#` 12# +#
744 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 6# +#
745 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
748 C# (chr# ((ord# ch -# 0xF0#) `iShiftL#` 18# +#
749 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 12# +#
750 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `iShiftL#` 6# +#
751 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
754 ch = indexCharOffAddr# addr nh
756 unpackNBytes# :: Addr# -> Int# -> [Char]
757 unpackNBytes# _addr 0# = []
758 unpackNBytes# addr len# = unpack [] (len# -# 1#)
763 case indexCharOffAddr# addr i# of
764 ch -> unpack (C# ch : acc) (i# -# 1#)
767 "unpack" forall a . unpackCString# a = build (unpackFoldrCString# a)
768 "unpack-list" forall a . unpackFoldrCString# a (:) [] = unpackCStringList# a
769 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
771 -- There's a built-in rule (in PrelRules.lhs) for
772 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n