1 % -----------------------------------------------------------------------------
2 % $Id: PrelBase.lhs,v 1.54 2001/10/02 16:15:10 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
455 eqString [] [] = True
456 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
457 eqString cs1 cs2 = False
459 {-# RULES "eqString" (==) = eqString #-}
463 %*********************************************************
465 \subsection{Type @Int@}
467 %*********************************************************
472 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
477 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
478 #if WORD_SIZE_IN_BITS == 31
479 minInt = I# (-0x40000000#)
480 maxInt = I# 0x3FFFFFFF#
481 #elif WORD_SIZE_IN_BITS == 32
482 minInt = I# (-0x80000000#)
483 maxInt = I# 0x7FFFFFFF#
485 minInt = I# (-0x8000000000000000#)
486 maxInt = I# 0x7FFFFFFFFFFFFFFF#
489 instance Eq Int where
493 instance Ord Int where
500 compareInt :: Int -> Int -> Ordering
501 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
503 compareInt# :: Int# -> Int# -> Ordering
511 %*********************************************************
513 \subsection{The function type}
515 %*********************************************************
526 -- function composition
528 (.) :: (b -> c) -> (a -> b) -> a -> c
531 -- flip f takes its (first) two arguments in the reverse order of f.
532 flip :: (a -> b -> c) -> b -> a -> c
535 -- right-associating infix application operator (useful in continuation-
538 ($) :: (a -> b) -> a -> b
541 -- until p f yields the result of applying f until p holds.
542 until :: (a -> Bool) -> (a -> a) -> a -> a
543 until p f x | p x = x
544 | otherwise = until p f (f x)
546 -- asTypeOf is a type-restricted version of const. It is usually used
547 -- as an infix operator, and its typing forces its first argument
548 -- (which is usually overloaded) to have the same type as the second.
549 asTypeOf :: a -> a -> a
553 %*********************************************************
555 \subsection{CCallable instances}
557 %*********************************************************
559 Defined here to avoid orphans
562 instance CCallable Char
563 instance CReturnable Char
565 instance CCallable Int
566 instance CReturnable Int
568 instance CReturnable () -- Why, exactly?
572 %*********************************************************
574 \subsection{Generics}
576 %*********************************************************
580 data a :+: b = Inl a | Inr b
581 data a :*: b = a :*: b
585 %*********************************************************
587 \subsection{Numeric primops}
589 %*********************************************************
592 divInt#, modInt# :: Int# -> Int# -> Int#
594 | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
595 | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
596 | otherwise = x# `quotInt#` y#
598 | (x# ># 0#) && (y# <# 0#) ||
599 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
605 Definitions of the boxed PrimOps; these will be
606 used in the case of partial applications, etc.
615 {-# INLINE plusInt #-}
616 {-# INLINE minusInt #-}
617 {-# INLINE timesInt #-}
618 {-# INLINE quotInt #-}
619 {-# INLINE remInt #-}
620 {-# INLINE negateInt #-}
622 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
623 (I# x) `plusInt` (I# y) = I# (x +# y)
624 (I# x) `minusInt` (I# y) = I# (x -# y)
625 (I# x) `timesInt` (I# y) = I# (x *# y)
626 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
627 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
628 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
629 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
632 "x# +# 0#" forall x#. x# +# 0# = x#
633 "0# +# x#" forall x#. 0# +# x# = x#
634 "x# -# 0#" forall x#. x# -# 0# = x#
635 "x# -# x#" forall x#. x# -# x# = 0#
636 "x# *# 0#" forall x#. x# *# 0# = 0#
637 "0# *# x#" forall x#. 0# *# x# = 0#
638 "x# *# 1#" forall x#. x# *# 1# = x#
639 "1# *# x#" forall x#. 1# *# x# = x#
642 gcdInt (I# a) (I# b) = g a b
643 where g 0# 0# = error "PrelBase.gcdInt: gcd 0 0 is undefined"
646 g _ _ = I# (gcdInt# absA absB)
648 absInt x = if x <# 0# then negateInt# x else x
653 negateInt :: Int -> Int
654 negateInt (I# x) = I# (negateInt# x)
656 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
657 (I# x) `gtInt` (I# y) = x ># y
658 (I# x) `geInt` (I# y) = x >=# y
659 (I# x) `eqInt` (I# y) = x ==# y
660 (I# x) `neInt` (I# y) = x /=# y
661 (I# x) `ltInt` (I# y) = x <# y
662 (I# x) `leInt` (I# y) = x <=# y
665 "x# ># x#" forall x#. x# ># x# = False
666 "x# >=# x#" forall x#. x# >=# x# = True
667 "x# ==# x#" forall x#. x# ==# x# = True
668 "x# /=# x#" forall x#. x# /=# x# = False
669 "x# <# x#" forall x#. x# <# x# = False
670 "x# <=# x#" forall x#. x# <=# x# = True
673 #if WORD_SIZE_IN_BITS == 32
675 "narrow32Int#" forall x#. narrow32Int# x# = x#
676 "narrow32Word#" forall x#. narrow32Word# x# = x#
681 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
682 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
687 %********************************************************
689 \subsection{Unpacking C strings}
691 %********************************************************
693 This code is needed for virtually all programs, since it's used for
694 unpacking the strings of error messages.
697 unpackCString# :: Addr# -> [Char]
698 {-# NOINLINE [1] unpackCString# #-}
699 unpackCString# a = unpackCStringList# a
701 unpackCStringList# :: Addr# -> [Char]
702 unpackCStringList# addr
706 | ch `eqChar#` '\0'# = []
707 | otherwise = C# ch : unpack (nh +# 1#)
709 ch = indexCharOffAddr# addr nh
711 unpackAppendCString# :: Addr# -> [Char] -> [Char]
712 unpackAppendCString# addr rest
716 | ch `eqChar#` '\0'# = rest
717 | otherwise = C# ch : unpack (nh +# 1#)
719 ch = indexCharOffAddr# addr nh
721 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
722 {-# NOINLINE [0] unpackFoldrCString# #-}
723 -- Don't inline till right at the end;
724 -- usually the unpack-list rule turns it into unpackCStringList
725 unpackFoldrCString# addr f z
729 | ch `eqChar#` '\0'# = z
730 | otherwise = C# ch `f` unpack (nh +# 1#)
732 ch = indexCharOffAddr# addr nh
734 unpackCStringUtf8# :: Addr# -> [Char]
735 unpackCStringUtf8# addr
739 | ch `eqChar#` '\0'# = []
740 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
741 | ch `leChar#` '\xDF'# =
742 C# (chr# ((ord# ch -# 0xC0#) `iShiftL#` 6# +#
743 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
745 | ch `leChar#` '\xEF'# =
746 C# (chr# ((ord# ch -# 0xE0#) `iShiftL#` 12# +#
747 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 6# +#
748 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
751 C# (chr# ((ord# ch -# 0xF0#) `iShiftL#` 18# +#
752 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 12# +#
753 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `iShiftL#` 6# +#
754 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
757 ch = indexCharOffAddr# addr nh
759 unpackNBytes# :: Addr# -> Int# -> [Char]
760 unpackNBytes# _addr 0# = []
761 unpackNBytes# addr len# = unpack [] (len# -# 1#)
766 case indexCharOffAddr# addr i# of
767 ch -> unpack (C# ch : acc) (i# -# 1#)
770 "unpack" forall a . unpackCString# a = build (unpackFoldrCString# a)
771 "unpack-list" forall a . unpackFoldrCString# a (:) [] = unpackCStringList# a
772 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
774 -- There's a built-in rule (in PrelRules.lhs) for
775 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n