1 % -----------------------------------------------------------------------------
2 % $Id: PrelBase.lhs,v 1.45 2001/04/14 22:28:22 qrczak 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] #-}
220 compare [] (_:_) = LT
221 compare (_:_) [] = GT
222 compare (x:xs) (y:ys) = case compare x y of
226 instance Functor [] where
229 instance Monad [] where
230 m >>= k = foldr ((++) . k) [] m
231 m >> k = foldr ((++) . (\ _ -> k)) [] m
236 A few list functions that appear here because they are used here.
237 The rest of the prelude list functions are in PrelList.
239 ----------------------------------------------
240 -- foldr/build/augment
241 ----------------------------------------------
244 foldr :: (a -> b -> b) -> b -> [a] -> b
246 -- foldr f z (x:xs) = f x (foldr f z xs)
251 go (y:ys) = y `k` go ys
253 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
254 {-# INLINE 2 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 "2" says to inline in phase 2
264 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
265 {-# INLINE 2 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]
302 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
303 mapFB c f x ys = c (f x) ys
305 mapList :: (a -> b) -> [a] -> [b]
307 mapList f (x:xs) = f x : mapList f xs
310 "map" forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
311 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
312 "mapList" forall f. foldr (mapFB (:) f) [] = mapList f
317 ----------------------------------------------
319 ----------------------------------------------
321 (++) :: [a] -> [a] -> [a]
325 "++" forall xs ys. (++) xs ys = augment (\c n -> foldr c n xs) ys
328 append :: [a] -> [a] -> [a]
330 append (x:xs) ys = x : append xs ys
334 %*********************************************************
336 \subsection{Type @Bool@}
338 %*********************************************************
341 data Bool = False | True deriving (Eq, Ord)
342 -- Read in PrelRead, Show in PrelShow
346 (&&), (||) :: Bool -> Bool -> Bool
361 %*********************************************************
363 \subsection{The @()@ type}
365 %*********************************************************
367 The Unit type is here because virtually any program needs it (whereas
368 some programs may get away without consulting PrelTup). Furthermore,
369 the renamer currently *always* asks for () to be in scope, so that
370 ccalls can use () as their default type; so when compiling PrelBase we
371 need (). (We could arrange suck in () only if -fglasgow-exts, but putting
372 it here seems more direct.)
381 instance Ord () where
392 %*********************************************************
394 \subsection{Type @Ordering@}
396 %*********************************************************
399 data Ordering = LT | EQ | GT deriving (Eq, Ord)
400 -- Read in PrelRead, Show in PrelShow
404 %*********************************************************
406 \subsection{Type @Char@ and @String@}
408 %*********************************************************
415 -- We don't use deriving for Eq and Ord, because for Ord the derived
416 -- instance defines only compare, which takes two primops. Then
417 -- '>' uses compare, and therefore takes two primops instead of one.
419 instance Eq Char where
420 (C# c1) == (C# c2) = c1 `eqChar#` c2
421 (C# c1) /= (C# c2) = c1 `neChar#` c2
423 instance Ord Char where
424 (C# c1) > (C# c2) = c1 `gtChar#` c2
425 (C# c1) >= (C# c2) = c1 `geChar#` c2
426 (C# c1) <= (C# c2) = c1 `leChar#` c2
427 (C# c1) < (C# c2) = c1 `ltChar#` c2
430 chr (I# i) | i >=# 0# && i <=# 0x10FFFF# = C# (chr# i)
431 | otherwise = error "Prelude.chr: bad argument"
433 unsafeChr :: Int -> Char
434 unsafeChr (I# i) = C# (chr# i)
437 ord (C# c) = I# (ord# c)
440 String equality is used when desugaring pattern-matches against strings.
443 eqString :: String -> String -> Bool
447 %*********************************************************
449 \subsection{Type @Int@}
451 %*********************************************************
456 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
460 #if WORD_SIZE_IN_BYTES == 4
461 minInt = I# (-0x80000000#)
462 maxInt = I# 0x7FFFFFFF#
464 minInt = I# (-0x8000000000000000#)
465 maxInt = I# 0x7FFFFFFFFFFFFFFF#
468 instance Eq Int where
472 instance Ord Int where
480 compareInt :: Int -> Int -> Ordering
481 (I# x) `compareInt` (I# y) = compareInt# x y
483 compareInt# :: Int# -> Int# -> Ordering
491 %*********************************************************
493 \subsection{The function type}
495 %*********************************************************
506 -- function composition
508 (.) :: (b -> c) -> (a -> b) -> a -> c
511 -- flip f takes its (first) two arguments in the reverse order of f.
512 flip :: (a -> b -> c) -> b -> a -> c
515 -- right-associating infix application operator (useful in continuation-
518 ($) :: (a -> b) -> a -> b
521 -- until p f yields the result of applying f until p holds.
522 until :: (a -> Bool) -> (a -> a) -> a -> a
523 until p f x | p x = x
524 | otherwise = until p f (f x)
526 -- asTypeOf is a type-restricted version of const. It is usually used
527 -- as an infix operator, and its typing forces its first argument
528 -- (which is usually overloaded) to have the same type as the second.
529 asTypeOf :: a -> a -> a
533 %*********************************************************
535 \subsection{CCallable instances}
537 %*********************************************************
539 Defined here to avoid orphans
542 instance CCallable Char
543 instance CReturnable Char
545 instance CCallable Int
546 instance CReturnable Int
548 instance CReturnable () -- Why, exactly?
552 %*********************************************************
554 \subsection{Generics}
556 %*********************************************************
560 data a :+: b = Inl a | Inr b
561 data a :*: b = a :*: b
565 %*********************************************************
567 \subsection{Numeric primops}
569 %*********************************************************
572 divInt#, modInt# :: Int# -> Int# -> Int#
574 | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
575 | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
576 | otherwise = x# `quotInt#` y#
578 | (x# ># 0#) && (y# <# 0#) ||
579 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
585 Definitions of the boxed PrimOps; these will be
586 used in the case of partial applications, etc.
595 {-# INLINE plusInt #-}
596 {-# INLINE minusInt #-}
597 {-# INLINE timesInt #-}
598 {-# INLINE quotInt #-}
599 {-# INLINE remInt #-}
600 {-# INLINE negateInt #-}
602 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
603 (I# x) `plusInt` (I# y) = I# (x +# y)
604 (I# x) `minusInt` (I# y) = I# (x -# y)
605 (I# x) `timesInt` (I# y) = I# (x *# y)
606 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
607 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
608 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
609 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
611 gcdInt (I# a) (I# b) = g a b
612 where g 0# 0# = error "PrelBase.gcdInt: gcd 0 0 is undefined"
615 g _ _ = I# (gcdInt# absA absB)
617 absInt x = if x <# 0# then negateInt# x else x
622 negateInt :: Int -> Int
623 negateInt (I# x) = I# (negateInt# x)
625 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
626 (I# x) `gtInt` (I# y) = x ># y
627 (I# x) `geInt` (I# y) = x >=# y
628 (I# x) `eqInt` (I# y) = x ==# y
629 (I# x) `neInt` (I# y) = x /=# y
630 (I# x) `ltInt` (I# y) = x <# y
631 (I# x) `leInt` (I# y) = x <=# y
633 #if WORD_SIZE_IN_BYTES == 4
635 "intToInt32#" forall x#. intToInt32# x# = x#
636 "wordToWord32#" forall x#. wordToWord32# x# = x#
641 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
642 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
647 %********************************************************
649 \subsection{Unpacking C strings}
651 %********************************************************
653 This code is needed for virtually all programs, since it's used for
654 unpacking the strings of error messages.
657 unpackCString# :: Addr# -> [Char]
658 unpackCString# a = unpackCStringList# a
660 unpackCStringList# :: Addr# -> [Char]
661 unpackCStringList# addr
665 | ch `eqChar#` '\0'# = []
666 | otherwise = C# ch : unpack (nh +# 1#)
668 ch = indexCharOffAddr# addr nh
670 unpackAppendCString# :: Addr# -> [Char] -> [Char]
671 unpackAppendCString# addr rest
675 | ch `eqChar#` '\0'# = rest
676 | otherwise = C# ch : unpack (nh +# 1#)
678 ch = indexCharOffAddr# addr nh
680 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
681 unpackFoldrCString# addr f z
685 | ch `eqChar#` '\0'# = z
686 | otherwise = C# ch `f` unpack (nh +# 1#)
688 ch = indexCharOffAddr# addr nh
690 unpackCStringUtf8# :: Addr# -> [Char]
691 unpackCStringUtf8# addr
695 | ch `eqChar#` '\0'# = []
696 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
697 | ch `leChar#` '\xDF'# =
698 C# (chr# ((ord# ch -# 0xC0#) `iShiftL#` 6# +#
699 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
701 | ch `leChar#` '\xEF'# =
702 C# (chr# ((ord# ch -# 0xE0#) `iShiftL#` 12# +#
703 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 6# +#
704 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
707 C# (chr# ((ord# ch -# 0xF0#) `iShiftL#` 18# +#
708 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `iShiftL#` 12# +#
709 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `iShiftL#` 6# +#
710 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
713 ch = indexCharOffAddr# addr nh
715 unpackNBytes# :: Addr# -> Int# -> [Char]
716 unpackNBytes# _addr 0# = []
717 unpackNBytes# addr len# = unpack [] (len# -# 1#)
722 case indexCharOffAddr# addr i# of
723 ch -> unpack (C# ch : acc) (i# -# 1#)
726 "unpack" forall a . unpackCString# a = build (unpackFoldrCString# a)
727 "unpack-list" forall a . unpackFoldrCString# a (:) [] = unpackCStringList# a
728 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
730 -- There's a built-in rule (in PrelRules.lhs) for
731 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n