1 \section[GHC.Base]{Module @GHC.Base@}
3 The overall structure of the GHC Prelude is a bit tricky.
5 a) We want to avoid "orphan modules", i.e. ones with instance
6 decls that don't belong either to a tycon or a class
7 defined in the same module
9 b) We want to avoid giant modules
11 So the rough structure is as follows, in (linearised) dependency order
14 GHC.Prim Has no implementation. It defines built-in things, and
15 by importing it you bring them into scope.
16 The source file is GHC.Prim.hi-boot, which is just
17 copied to make GHC.Prim.hi
19 GHC.Base Classes: Eq, Ord, Functor, Monad
20 Types: list, (), Int, Bool, Ordering, Char, String
22 Data.Tuple Types: tuples, plus instances for GHC.Base classes
24 GHC.Show Class: Show, plus instances for GHC.Base/GHC.Tup types
26 GHC.Enum Class: Enum, plus instances for GHC.Base/GHC.Tup types
28 Data.Maybe Type: Maybe, plus instances for GHC.Base classes
30 GHC.List List functions
32 GHC.Num Class: Num, plus instances for Int
33 Type: Integer, plus instances for all classes so far (Eq, Ord, Num, Show)
35 Integer is needed here because it is mentioned in the signature
36 of 'fromInteger' in class Num
38 GHC.Real Classes: Real, Integral, Fractional, RealFrac
39 plus instances for Int, Integer
40 Types: Ratio, Rational
41 plus intances for classes so far
43 Rational is needed here because it is mentioned in the signature
44 of 'toRational' in class Real
46 GHC.ST The ST monad, instances and a few helper functions
48 Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
50 GHC.Arr Types: Array, MutableArray, MutableVar
52 Arrays are used by a function in GHC.Float
54 GHC.Float Classes: Floating, RealFloat
55 Types: Float, Double, plus instances of all classes so far
57 This module contains everything to do with floating point.
58 It is a big module (900 lines)
59 With a bit of luck, many modules can be compiled without ever reading GHC.Float.hi
62 Other Prelude modules are much easier with fewer complex dependencies.
71 , ExistentialQuantification
74 -- -fno-warn-orphans is needed for things like:
75 -- Orphan rule: "x# -# x#" ALWAYS forall x# :: Int# -# x# x# = 0
76 {-# OPTIONS_GHC -fno-warn-orphans #-}
77 {-# OPTIONS_HADDOCK hide #-}
79 -----------------------------------------------------------------------------
82 -- Copyright : (c) The University of Glasgow, 1992-2002
83 -- License : see libraries/base/LICENSE
85 -- Maintainer : cvs-ghc@haskell.org
86 -- Stability : internal
87 -- Portability : non-portable (GHC extensions)
89 -- Basic data types and classes.
91 -----------------------------------------------------------------------------
103 module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
104 module GHC.Err -- of people having to import it explicitly
113 import {-# SOURCE #-} GHC.Show
114 import {-# SOURCE #-} GHC.Err
115 import {-# SOURCE #-} GHC.IO (failIO)
117 -- These two are not strictly speaking required by this module, but they are
118 -- implicit dependencies whenever () or tuples are mentioned, so adding them
119 -- as imports here helps to get the dependencies right in the new build system.
129 default () -- Double isn't available yet
133 %*********************************************************
135 \subsection{DEBUGGING STUFF}
136 %* (for use when compiling GHC.Base itself doesn't work)
138 %*********************************************************
142 data Bool = False | True
143 data Ordering = LT | EQ | GT
151 (&&) True True = True
157 unpackCString# :: Addr# -> [Char]
158 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
159 unpackAppendCString# :: Addr# -> [Char] -> [Char]
160 unpackCStringUtf8# :: Addr# -> [Char]
161 unpackCString# a = error "urk"
162 unpackFoldrCString# a = error "urk"
163 unpackAppendCString# a = error "urk"
164 unpackCStringUtf8# a = error "urk"
169 %*********************************************************
171 \subsection{Monadic classes @Functor@, @Monad@ }
173 %*********************************************************
176 {- | The 'Functor' class is used for types that can be mapped over.
177 Instances of 'Functor' should satisfy the following laws:
180 > fmap (f . g) == fmap f . fmap g
182 The instances of 'Functor' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
186 class Functor f where
187 fmap :: (a -> b) -> f a -> f b
189 -- | Replace all locations in the input with the same value.
190 -- The default definition is @'fmap' . 'const'@, but this may be
191 -- overridden with a more efficient version.
192 (<$) :: a -> f b -> f a
195 {- | The 'Monad' class defines the basic operations over a /monad/,
196 a concept from a branch of mathematics known as /category theory/.
197 From the perspective of a Haskell programmer, however, it is best to
198 think of a monad as an /abstract datatype/ of actions.
199 Haskell's @do@ expressions provide a convenient syntax for writing
202 Minimal complete definition: '>>=' and 'return'.
204 Instances of 'Monad' should satisfy the following laws:
206 > return a >>= k == k a
208 > m >>= (\x -> k x >>= h) == (m >>= k) >>= h
210 Instances of both 'Monad' and 'Functor' should additionally satisfy the law:
212 > fmap f xs == xs >>= return . f
214 The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
215 defined in the "Prelude" satisfy these laws.
219 -- | Sequentially compose two actions, passing any value produced
220 -- by the first as an argument to the second.
221 (>>=) :: forall a b. m a -> (a -> m b) -> m b
222 -- | Sequentially compose two actions, discarding any value produced
223 -- by the first, like sequencing operators (such as the semicolon)
224 -- in imperative languages.
225 (>>) :: forall a b. m a -> m b -> m b
226 -- Explicit for-alls so that we know what order to
227 -- give type arguments when desugaring
229 -- | Inject a value into the monadic type.
231 -- | Fail with a message. This operation is not part of the
232 -- mathematical definition of a monad, but is invoked on pattern-match
233 -- failure in a @do@ expression.
234 fail :: String -> m a
237 m >> k = m >>= \_ -> k
242 %*********************************************************
244 \subsection{The list type}
246 %*********************************************************
249 instance Functor [] where
252 instance Monad [] where
253 m >>= k = foldr ((++) . k) [] m
254 m >> k = foldr ((++) . (\ _ -> k)) [] m
259 A few list functions that appear here because they are used here.
260 The rest of the prelude list functions are in GHC.List.
262 ----------------------------------------------
263 -- foldr/build/augment
264 ----------------------------------------------
267 -- | 'foldr', applied to a binary operator, a starting value (typically
268 -- the right-identity of the operator), and a list, reduces the list
269 -- using the binary operator, from right to left:
271 -- > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
273 foldr :: (a -> b -> b) -> b -> [a] -> b
275 -- foldr f z (x:xs) = f x (foldr f z xs)
276 {-# INLINE [0] foldr #-}
277 -- Inline only in the final stage, after the foldr/cons rule has had a chance
278 -- Also note that we inline it when it has *two* parameters, which are the
279 -- ones we are keen about specialising!
283 go (y:ys) = y `k` go ys
285 -- | A list producer that can be fused with 'foldr'.
286 -- This function is merely
288 -- > build g = g (:) []
290 -- but GHC's simplifier will transform an expression of the form
291 -- @'foldr' k z ('build' g)@, which may arise after inlining, to @g k z@,
292 -- which avoids producing an intermediate list.
294 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
295 {-# INLINE [1] build #-}
296 -- The INLINE is important, even though build is tiny,
297 -- because it prevents [] getting inlined in the version that
298 -- appears in the interface file. If [] *is* inlined, it
299 -- won't match with [] appearing in rules in an importing module.
301 -- The "1" says to inline in phase 1
305 -- | A list producer that can be fused with 'foldr'.
306 -- This function is merely
308 -- > augment g xs = g (:) xs
310 -- but GHC's simplifier will transform an expression of the form
311 -- @'foldr' k z ('augment' g xs)@, which may arise after inlining, to
312 -- @g k ('foldr' k z xs)@, which avoids producing an intermediate list.
314 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
315 {-# INLINE [1] augment #-}
316 augment g xs = g (:) xs
319 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
320 foldr k z (build g) = g k z
322 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
323 foldr k z (augment g xs) = g k (foldr k z xs)
325 "foldr/id" foldr (:) [] = \x -> x
326 "foldr/app" [1] forall ys. foldr (:) ys = \xs -> xs ++ ys
327 -- Only activate this from phase 1, because that's
328 -- when we disable the rule that expands (++) into foldr
330 -- The foldr/cons rule looks nice, but it can give disastrously
331 -- bloated code when commpiling
332 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
333 -- i.e. when there are very very long literal lists
334 -- So I've disabled it for now. We could have special cases
335 -- for short lists, I suppose.
336 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
338 "foldr/single" forall k z x. foldr k z [x] = k x z
339 "foldr/nil" forall k z. foldr k z [] = z
341 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
342 (h::forall b. (a->b->b) -> b -> b) .
343 augment g (build h) = build (\c n -> g c (h c n))
344 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
345 augment g [] = build g
348 -- This rule is true, but not (I think) useful:
349 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
353 ----------------------------------------------
355 ----------------------------------------------
358 -- | 'map' @f xs@ is the list obtained by applying @f@ to each element
361 -- > map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
362 -- > map f [x1, x2, ...] == [f x1, f x2, ...]
364 map :: (a -> b) -> [a] -> [b]
366 map f (x:xs) = f x : map f xs
369 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
370 {-# INLINE [0] mapFB #-}
371 mapFB c f = \x ys -> c (f x) ys
373 -- The rules for map work like this.
375 -- Up to (but not including) phase 1, we use the "map" rule to
376 -- rewrite all saturated applications of map with its build/fold
377 -- form, hoping for fusion to happen.
378 -- In phase 1 and 0, we switch off that rule, inline build, and
379 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
380 -- thing back into plain map.
382 -- It's important that these two rules aren't both active at once
383 -- (along with build's unfolding) else we'd get an infinite loop
384 -- in the rules. Hence the activation control below.
386 -- The "mapFB" rule optimises compositions of map.
388 -- This same pattern is followed by many other functions:
389 -- e.g. append, filter, iterate, repeat, etc.
392 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
393 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
394 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
399 ----------------------------------------------
401 ----------------------------------------------
403 -- | Append two lists, i.e.,
405 -- > [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
406 -- > [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
408 -- If the first list is not finite, the result is the first list.
410 (++) :: [a] -> [a] -> [a]
412 (++) (x:xs) ys = x : xs ++ ys
415 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
421 %*********************************************************
423 \subsection{Type @Bool@}
425 %*********************************************************
428 -- |'otherwise' is defined as the value 'True'. It helps to make
429 -- guards more readable. eg.
431 -- > f x | x < 0 = ...
432 -- > | otherwise = ...
437 %*********************************************************
439 \subsection{Type @Char@ and @String@}
441 %*********************************************************
444 -- | A 'String' is a list of characters. String constants in Haskell are values
450 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
451 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
452 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
453 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
454 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
455 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
458 -- | The 'Prelude.toEnum' method restricted to the type 'Data.Char.Char'.
461 | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
463 = error ("Prelude.chr: bad argument: " ++ showSignedInt (I# 9#) i "")
465 unsafeChr :: Int -> Char
466 unsafeChr (I# i#) = C# (chr# i#)
468 -- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
470 ord (C# c#) = I# (ord# c#)
473 String equality is used when desugaring pattern-matches against strings.
476 eqString :: String -> String -> Bool
477 eqString [] [] = True
478 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
481 {-# RULES "eqString" (==) = eqString #-}
482 -- eqString also has a BuiltInRule in PrelRules.lhs:
483 -- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
487 %*********************************************************
489 \subsection{Type @Int@}
491 %*********************************************************
494 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
499 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
500 #if WORD_SIZE_IN_BITS == 31
501 minInt = I# (-0x40000000#)
502 maxInt = I# 0x3FFFFFFF#
503 #elif WORD_SIZE_IN_BITS == 32
504 minInt = I# (-0x80000000#)
505 maxInt = I# 0x7FFFFFFF#
507 minInt = I# (-0x8000000000000000#)
508 maxInt = I# 0x7FFFFFFFFFFFFFFF#
511 instance Eq Int where
515 instance Ord Int where
522 compareInt :: Int -> Int -> Ordering
523 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
525 compareInt# :: Int# -> Int# -> Ordering
533 %*********************************************************
535 \subsection{The function type}
537 %*********************************************************
540 -- | Identity function.
544 -- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
545 -- magical strictness property: it is lazy in its first argument,
546 -- even though its semantics is strict.
549 -- Implementation note: its strictness and unfolding are over-ridden
550 -- by the definition in MkId.lhs; in both cases to nothing at all.
551 -- That way, 'lazy' does not get inlined, and the strictness analyser
552 -- sees it as lazy. Then the worker/wrapper phase inlines it.
555 -- Assertion function. This simply ignores its boolean argument.
556 -- The compiler may rewrite it to @('assertError' line)@.
558 -- | If the first argument evaluates to 'True', then the result is the
559 -- second argument. Otherwise an 'AssertionFailed' exception is raised,
560 -- containing a 'String' with the source file and line number of the
563 -- Assertions can normally be turned on or off with a compiler flag
564 -- (for GHC, assertions are normally on unless optimisation is turned on
565 -- with @-O@ or the @-fignore-asserts@
566 -- option is given). When assertions are turned off, the first
567 -- argument to 'assert' is ignored, and the second argument is
568 -- returned as the result.
570 -- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
571 -- but from Template Haskell onwards it's simply
572 -- defined here in Base.lhs
573 assert :: Bool -> a -> a
579 breakpointCond :: Bool -> a -> a
580 breakpointCond _ r = r
582 data Opaque = forall a. O a
584 -- | Constant function.
588 -- | Function composition.
590 -- Make sure it has TWO args only on the left, so that it inlines
591 -- when applied to two functions, even if there is no final argument
592 (.) :: (b -> c) -> (a -> b) -> a -> c
593 (.) f g = \x -> f (g x)
595 -- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
596 flip :: (a -> b -> c) -> b -> a -> c
599 -- | Application operator. This operator is redundant, since ordinary
600 -- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
601 -- low, right-associative binding precedence, so it sometimes allows
602 -- parentheses to be omitted; for example:
604 -- > f $ g $ h x = f (g (h x))
606 -- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
607 -- or @'Data.List.zipWith' ('$') fs xs@.
609 ($) :: (a -> b) -> a -> b
612 -- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
613 until :: (a -> Bool) -> (a -> a) -> a -> a
614 until p f x | p x = x
615 | otherwise = until p f (f x)
617 -- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
618 -- used as an infix operator, and its typing forces its first argument
619 -- (which is usually overloaded) to have the same type as the second.
620 asTypeOf :: a -> a -> a
624 %*********************************************************
626 \subsection{@Functor@ and @Monad@ instances for @IO@}
628 %*********************************************************
631 instance Functor IO where
632 fmap f x = x >>= (return . f)
634 instance Monad IO where
635 {-# INLINE return #-}
638 m >> k = m >>= \ _ -> k
641 fail s = GHC.IO.failIO s
643 returnIO :: a -> IO a
644 returnIO x = IO $ \ s -> (# s, x #)
646 bindIO :: IO a -> (a -> IO b) -> IO b
647 bindIO (IO m) k = IO $ \ s -> case m s of (# new_s, a #) -> unIO (k a) new_s
649 thenIO :: IO a -> IO b -> IO b
650 thenIO (IO m) k = IO $ \ s -> case m s of (# new_s, _ #) -> unIO k new_s
652 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
656 %*********************************************************
658 \subsection{@getTag@}
660 %*********************************************************
662 Returns the 'tag' of a constructor application; this function is used
663 by the deriving code for Eq, Ord and Enum.
665 The primitive dataToTag# requires an evaluated constructor application
666 as its argument, so we provide getTag as a wrapper that performs the
667 evaluation before calling dataToTag#. We could have dataToTag#
668 evaluate its argument, but we prefer to do it this way because (a)
669 dataToTag# can be an inline primop if it doesn't need to do any
670 evaluation, and (b) we want to expose the evaluation to the
671 simplifier, because it might be possible to eliminate the evaluation
672 in the case when the argument is already known to be evaluated.
675 {-# INLINE getTag #-}
677 getTag x = x `seq` dataToTag# x
680 %*********************************************************
682 \subsection{Numeric primops}
684 %*********************************************************
687 divInt# :: Int# -> Int# -> Int#
689 -- Be careful NOT to overflow if we do any additional arithmetic
690 -- on the arguments... the following previous version of this
691 -- code has problems with overflow:
692 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
693 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
694 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
695 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
696 | otherwise = x# `quotInt#` y#
698 modInt# :: Int# -> Int# -> Int#
700 | (x# ># 0#) && (y# <# 0#) ||
701 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
704 !r# = x# `remInt#` y#
707 Definitions of the boxed PrimOps; these will be
708 used in the case of partial applications, etc.
717 {-# INLINE plusInt #-}
718 {-# INLINE minusInt #-}
719 {-# INLINE timesInt #-}
720 {-# INLINE quotInt #-}
721 {-# INLINE remInt #-}
722 {-# INLINE negateInt #-}
724 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt :: Int -> Int -> Int
725 (I# x) `plusInt` (I# y) = I# (x +# y)
726 (I# x) `minusInt` (I# y) = I# (x -# y)
727 (I# x) `timesInt` (I# y) = I# (x *# y)
728 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
729 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
730 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
731 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
734 "x# +# 0#" forall x#. x# +# 0# = x#
735 "0# +# x#" forall x#. 0# +# x# = x#
736 "x# -# 0#" forall x#. x# -# 0# = x#
737 "x# -# x#" forall x#. x# -# x# = 0#
738 "x# *# 0#" forall x#. x# *# 0# = 0#
739 "0# *# x#" forall x#. 0# *# x# = 0#
740 "x# *# 1#" forall x#. x# *# 1# = x#
741 "1# *# x#" forall x#. 1# *# x# = x#
744 negateInt :: Int -> Int
745 negateInt (I# x) = I# (negateInt# x)
747 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
748 (I# x) `gtInt` (I# y) = x ># y
749 (I# x) `geInt` (I# y) = x >=# y
750 (I# x) `eqInt` (I# y) = x ==# y
751 (I# x) `neInt` (I# y) = x /=# y
752 (I# x) `ltInt` (I# y) = x <# y
753 (I# x) `leInt` (I# y) = x <=# y
756 "x# ># x#" forall x#. x# ># x# = False
757 "x# >=# x#" forall x#. x# >=# x# = True
758 "x# ==# x#" forall x#. x# ==# x# = True
759 "x# /=# x#" forall x#. x# /=# x# = False
760 "x# <# x#" forall x#. x# <# x# = False
761 "x# <=# x#" forall x#. x# <=# x# = True
765 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
766 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
767 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
768 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
769 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
770 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
771 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
772 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
773 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
777 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
778 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
779 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
780 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
781 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
782 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
786 We'd like to have more rules, but for example:
788 This gives wrong answer (0) for NaN - NaN (should be NaN):
789 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
791 This gives wrong answer (0) for 0 * NaN (should be NaN):
792 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
794 This gives wrong answer (0) for NaN * 0 (should be NaN):
795 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
797 These are tested by num014.
800 -- Wrappers for the shift operations. The uncheckedShift# family are
801 -- undefined when the amount being shifted by is greater than the size
802 -- in bits of Int#, so these wrappers perform a check and return
803 -- either zero or -1 appropriately.
805 -- Note that these wrappers still produce undefined results when the
806 -- second argument (the shift amount) is negative.
808 -- | Shift the argument left by the specified number of bits
809 -- (which must be non-negative).
810 shiftL# :: Word# -> Int# -> Word#
811 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
812 | otherwise = a `uncheckedShiftL#` b
814 -- | Shift the argument right by the specified number of bits
815 -- (which must be non-negative).
816 shiftRL# :: Word# -> Int# -> Word#
817 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
818 | otherwise = a `uncheckedShiftRL#` b
820 -- | Shift the argument left by the specified number of bits
821 -- (which must be non-negative).
822 iShiftL# :: Int# -> Int# -> Int#
823 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
824 | otherwise = a `uncheckedIShiftL#` b
826 -- | Shift the argument right (signed) by the specified number of bits
827 -- (which must be non-negative).
828 iShiftRA# :: Int# -> Int# -> Int#
829 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
830 | otherwise = a `uncheckedIShiftRA#` b
832 -- | Shift the argument right (unsigned) by the specified number of bits
833 -- (which must be non-negative).
834 iShiftRL# :: Int# -> Int# -> Int#
835 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
836 | otherwise = a `uncheckedIShiftRL#` b
838 #if WORD_SIZE_IN_BITS == 32
840 "narrow32Int#" forall x#. narrow32Int# x# = x#
841 "narrow32Word#" forall x#. narrow32Word# x# = x#
846 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
847 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
852 %********************************************************
854 \subsection{Unpacking C strings}
856 %********************************************************
858 This code is needed for virtually all programs, since it's used for
859 unpacking the strings of error messages.
862 unpackCString# :: Addr# -> [Char]
863 {-# NOINLINE unpackCString# #-}
864 -- There's really no point in inlining this, ever, cos
865 -- the loop doesn't specialise in an interesting
866 -- But it's pretty small, so there's a danger that
867 -- it'll be inlined at every literal, which is a waste
872 | ch `eqChar#` '\0'# = []
873 | otherwise = C# ch : unpack (nh +# 1#)
875 !ch = indexCharOffAddr# addr nh
877 unpackAppendCString# :: Addr# -> [Char] -> [Char]
878 {-# NOINLINE unpackAppendCString# #-}
879 -- See the NOINLINE note on unpackCString#
880 unpackAppendCString# addr rest
884 | ch `eqChar#` '\0'# = rest
885 | otherwise = C# ch : unpack (nh +# 1#)
887 !ch = indexCharOffAddr# addr nh
889 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
891 -- Usually the unpack-list rule turns unpackFoldrCString# into unpackCString#
893 -- It also has a BuiltInRule in PrelRules.lhs:
894 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
895 -- = unpackFoldrCString# "foobaz" c n
897 {-# NOINLINE unpackFoldrCString# #-}
898 -- At one stage I had NOINLINE [0] on the grounds that, unlike
899 -- unpackCString#, there *is* some point in inlining
900 -- unpackFoldrCString#, because we get better code for the
901 -- higher-order function call. BUT there may be a lot of
902 -- literal strings, and making a separate 'unpack' loop for
903 -- each is highly gratuitous. See nofib/real/anna/PrettyPrint.
905 unpackFoldrCString# addr f z
909 | ch `eqChar#` '\0'# = z
910 | otherwise = C# ch `f` unpack (nh +# 1#)
912 !ch = indexCharOffAddr# addr nh
914 unpackCStringUtf8# :: Addr# -> [Char]
915 unpackCStringUtf8# addr
919 | ch `eqChar#` '\0'# = []
920 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
921 | ch `leChar#` '\xDF'# =
922 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
923 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
925 | ch `leChar#` '\xEF'# =
926 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
927 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
928 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
931 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
932 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
933 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
934 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
937 !ch = indexCharOffAddr# addr nh
939 unpackNBytes# :: Addr# -> Int# -> [Char]
940 unpackNBytes# _addr 0# = []
941 unpackNBytes# addr len# = unpack [] (len# -# 1#)
946 case indexCharOffAddr# addr i# of
947 ch -> unpack (C# ch : acc) (i# -# 1#)
950 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
951 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
952 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
954 -- There's a built-in rule (in PrelRules.lhs) for
955 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
962 -- | A special argument for the 'Control.Monad.ST.ST' type constructor,
963 -- indexing a state embedded in the 'Prelude.IO' monad by
964 -- 'Control.Monad.ST.stToIO'.