1 % -----------------------------------------------------------------------------
2 % $Id: PrelBase.lhs,v 1.51 2001/08/17 17:18:54 apt 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)
250 go (y:ys) = y `k` go ys
252 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
253 {-# INLINE 2 build #-}
254 -- The INLINE is important, even though build is tiny,
255 -- because it prevents [] getting inlined in the version that
256 -- appears in the interface file. If [] *is* inlined, it
257 -- won't match with [] appearing in rules in an importing module.
259 -- The "2" says to inline in phase 2
263 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
264 {-# INLINE 2 augment #-}
265 augment g xs = g (:) xs
268 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
269 foldr k z (build g) = g k z
271 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
272 foldr k z (augment g xs) = g k (foldr k z xs)
274 "foldr/id" foldr (:) [] = \x->x
275 "foldr/app" forall xs ys. foldr (:) ys xs = append xs ys
277 "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
278 "foldr/nil" forall k z. foldr k z [] = z
280 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
281 (h::forall b. (a->b->b) -> b -> b) .
282 augment g (build h) = build (\c n -> g c (h c n))
283 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
284 augment g [] = build g
287 -- This rule is true, but not (I think) useful:
288 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
292 ----------------------------------------------
294 ----------------------------------------------
297 map :: (a -> b) -> [a] -> [b]
301 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
302 mapFB c f x ys = c (f x) ys
304 mapList :: (a -> b) -> [a] -> [b]
306 mapList f (x:xs) = f x : mapList f xs
309 "map" forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
310 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
311 "mapList" forall f. foldr (mapFB (:) f) [] = mapList f
316 ----------------------------------------------
318 ----------------------------------------------
320 (++) :: [a] -> [a] -> [a]
324 "++" forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
327 append :: [a] -> [a] -> [a]
329 append (x:xs) ys = x : append xs ys
333 %*********************************************************
335 \subsection{Type @Bool@}
337 %*********************************************************
340 data Bool = False | True deriving (Eq, Ord)
341 -- Read in PrelRead, Show in PrelShow
345 (&&), (||) :: Bool -> Bool -> Bool
360 %*********************************************************
362 \subsection{The @()@ type}
364 %*********************************************************
366 The Unit type is here because virtually any program needs it (whereas
367 some programs may get away without consulting PrelTup). Furthermore,
368 the renamer currently *always* asks for () to be in scope, so that
369 ccalls can use () as their default type; so when compiling PrelBase we
370 need (). (We could arrange suck in () only if -fglasgow-exts, but putting
371 it here seems more direct.)
380 instance Ord () where
391 %*********************************************************
393 \subsection{Type @Ordering@}
395 %*********************************************************
398 data Ordering = LT | EQ | GT deriving (Eq, Ord)
399 -- Read in PrelRead, Show in PrelShow
403 %*********************************************************
405 \subsection{Type @Char@ and @String@}
407 %*********************************************************
414 -- We don't use deriving for Eq and Ord, because for Ord the derived
415 -- instance defines only compare, which takes two primops. Then
416 -- '>' uses compare, and therefore takes two primops instead of one.
418 instance Eq Char where
419 (C# c1) == (C# c2) = c1 `eqChar#` c2
420 (C# c1) /= (C# c2) = c1 `neChar#` c2
422 instance Ord Char where
423 (C# c1) > (C# c2) = c1 `gtChar#` c2
424 (C# c1) >= (C# c2) = c1 `geChar#` c2
425 (C# c1) <= (C# c2) = c1 `leChar#` c2
426 (C# c1) < (C# c2) = c1 `ltChar#` c2
429 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
430 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
431 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
432 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
433 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
434 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
438 chr (I# i#) | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
439 | otherwise = error "Prelude.chr: bad argument"
441 unsafeChr :: Int -> Char
442 unsafeChr (I# i#) = C# (chr# i#)
445 ord (C# c#) = I# (ord# c#)
448 String equality is used when desugaring pattern-matches against strings.
451 eqString :: String -> String -> Bool
455 %*********************************************************
457 \subsection{Type @Int@}
459 %*********************************************************
464 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
469 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
470 #if WORD_SIZE_IN_BITS == 31
471 minInt = I# (-0x40000000#)
472 maxInt = I# 0x3FFFFFFF#
473 #elif WORD_SIZE_IN_BITS == 32
474 minInt = I# (-0x80000000#)
475 maxInt = I# 0x7FFFFFFF#
477 minInt = I# (-0x8000000000000000#)
478 maxInt = I# 0x7FFFFFFFFFFFFFFF#
481 instance Eq Int where
485 instance Ord Int where
492 compareInt :: Int -> Int -> Ordering
493 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
495 compareInt# :: Int# -> Int# -> Ordering
503 %*********************************************************
505 \subsection{The function type}
507 %*********************************************************
518 -- function composition
520 (.) :: (b -> c) -> (a -> b) -> a -> c
523 -- flip f takes its (first) two arguments in the reverse order of f.
524 flip :: (a -> b -> c) -> b -> a -> c
527 -- right-associating infix application operator (useful in continuation-
530 ($) :: (a -> b) -> a -> b
533 -- until p f yields the result of applying f until p holds.
534 until :: (a -> Bool) -> (a -> a) -> a -> a
535 until p f x | p x = x
536 | otherwise = until p f (f x)
538 -- asTypeOf is a type-restricted version of const. It is usually used
539 -- as an infix operator, and its typing forces its first argument
540 -- (which is usually overloaded) to have the same type as the second.
541 asTypeOf :: a -> a -> a
545 %*********************************************************
547 \subsection{CCallable instances}
549 %*********************************************************
551 Defined here to avoid orphans
554 instance CCallable Char
555 instance CReturnable Char
557 instance CCallable Int
558 instance CReturnable Int
560 instance CReturnable () -- Why, exactly?
564 %*********************************************************
566 \subsection{Generics}
568 %*********************************************************
572 data a :+: b = Inl a | Inr b
573 data a :*: b = a :*: b
577 %*********************************************************
579 \subsection{Numeric primops}
581 %*********************************************************
584 divInt#, modInt# :: Int# -> Int# -> Int#
586 | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
587 | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
588 | otherwise = x# `quotInt#` y#
590 | (x# ># 0#) && (y# <# 0#) ||
591 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
597 Definitions of the boxed PrimOps; these will be
598 used in the case of partial applications, etc.
607 {-# INLINE plusInt #-}
608 {-# INLINE minusInt #-}
609 {-# INLINE timesInt #-}
610 {-# INLINE quotInt #-}
611 {-# INLINE remInt #-}
612 {-# INLINE negateInt #-}
614 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
615 (I# x) `plusInt` (I# y) = I# (x +# y)
616 (I# x) `minusInt` (I# y) = I# (x -# y)
617 (I# x) `timesInt` (I# y) = I# (x *# y)
618 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
619 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
620 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
621 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
624 "x# +# 0#" forall x#. x# +# 0# = x#
625 "0# +# x#" forall x#. 0# +# x# = x#
626 "x# -# 0#" forall x#. x# -# 0# = x#
627 "x# -# x#" forall x#. x# -# x# = 0#
628 "x# *# 0#" forall x#. x# *# 0# = 0#
629 "0# *# x#" forall x#. 0# *# x# = 0#
630 "x# *# 1#" forall x#. x# *# 1# = x#
631 "1# *# x#" forall x#. 1# *# x# = x#
634 gcdInt (I# a) (I# b) = g a b
635 where g 0# 0# = error "PrelBase.gcdInt: gcd 0 0 is undefined"
638 g _ _ = I# (gcdInt# absA absB)
640 absInt x = if x <# 0# then negateInt# x else x
645 negateInt :: Int -> Int
646 negateInt (I# x) = I# (negateInt# x)
648 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
649 (I# x) `gtInt` (I# y) = x ># y
650 (I# x) `geInt` (I# y) = x >=# y
651 (I# x) `eqInt` (I# y) = x ==# y
652 (I# x) `neInt` (I# y) = x /=# y
653 (I# x) `ltInt` (I# y) = x <# y
654 (I# x) `leInt` (I# y) = x <=# y
657 "x# ># x#" forall x#. x# ># x# = False
658 "x# >=# x#" forall x#. x# >=# x# = True
659 "x# ==# x#" forall x#. x# ==# x# = True
660 "x# /=# x#" forall x#. x# /=# x# = False
661 "x# <# x#" forall x#. x# <# x# = False
662 "x# <=# x#" forall x#. x# <=# x# = True
665 #if WORD_SIZE_IN_BITS == 32
667 "narrow32Int#" forall x#. narrow32Int# x# = x#
668 "narrow32Word#" forall x#. narrow32Word# x# = x#
673 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
674 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
679 %********************************************************
681 \subsection{Unpacking C strings}
683 %********************************************************
685 This code is needed for virtually all programs, since it's used for
686 unpacking the strings of error messages.
689 unpackCString# :: Addr# -> [Char]
690 unpackCString# a = unpackCStringList# a
692 unpackCStringList# :: Addr# -> [Char]
693 unpackCStringList# addr
697 | ch `eqChar#` '\0'# = []
698 | otherwise = C# ch : unpack (nh +# 1#)
700 ch = indexCharOffAddr# addr nh
702 unpackAppendCString# :: Addr# -> [Char] -> [Char]
703 unpackAppendCString# addr rest
707 | ch `eqChar#` '\0'# = rest
708 | otherwise = C# ch : unpack (nh +# 1#)
710 ch = indexCharOffAddr# addr nh
712 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
713 unpackFoldrCString# addr f z
717 | ch `eqChar#` '\0'# = z
718 | otherwise = C# ch `f` unpack (nh +# 1#)
720 ch = indexCharOffAddr# addr nh
722 unpackCStringUtf8# :: Addr# -> [Char]
723 unpackCStringUtf8# addr
727 | ch `eqChar#` '\0'# = []
728 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
729 | ch `leChar#` '\xDF'# =
730 C# (chr# ((ord# ch -# 0xC0#) `iShiftL#` 6# +#
731 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
733 | ch `leChar#` '\xEF'# =
734 C# (chr# ((ord# ch -# 0xE0#) `iShiftL#` 12# +#
735 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 6# +#
736 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
739 C# (chr# ((ord# ch -# 0xF0#) `iShiftL#` 18# +#
740 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 12# +#
741 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `iShiftL#` 6# +#
742 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
745 ch = indexCharOffAddr# addr nh
747 unpackNBytes# :: Addr# -> Int# -> [Char]
748 unpackNBytes# _addr 0# = []
749 unpackNBytes# addr len# = unpack [] (len# -# 1#)
754 case indexCharOffAddr# addr i# of
755 ch -> unpack (C# ch : acc) (i# -# 1#)
758 "unpack" forall a . unpackCString# a = build (unpackFoldrCString# a)
759 "unpack-list" forall a . unpackFoldrCString# a (:) [] = unpackCStringList# a
760 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
762 -- There's a built-in rule (in PrelRules.lhs) for
763 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n