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.
65 {-# OPTIONS_GHC -XNoImplicitPrelude #-}
66 -- -fno-warn-orphans is needed for things like:
67 -- Orphan rule: "x# -# x#" ALWAYS forall x# :: Int# -# x# x# = 0
68 {-# OPTIONS_GHC -fno-warn-orphans #-}
69 {-# OPTIONS_HADDOCK hide #-}
70 -----------------------------------------------------------------------------
73 -- Copyright : (c) The University of Glasgow, 1992-2002
74 -- License : see libraries/base/LICENSE
76 -- Maintainer : cvs-ghc@haskell.org
77 -- Stability : internal
78 -- Portability : non-portable (GHC extensions)
80 -- Basic data types and classes.
82 -----------------------------------------------------------------------------
94 module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
95 module GHC.Err -- of people having to import it explicitly
104 import {-# SOURCE #-} GHC.Show
105 import {-# SOURCE #-} GHC.Err
106 import {-# SOURCE #-} GHC.IO (failIO)
108 -- These two are not strictly speaking required by this module, but they are
109 -- implicit dependencies whenever () or tuples are mentioned, so adding them
110 -- as imports here helps to get the dependencies right in the new build system.
120 default () -- Double isn't available yet
124 %*********************************************************
126 \subsection{DEBUGGING STUFF}
127 %* (for use when compiling GHC.Base itself doesn't work)
129 %*********************************************************
133 data Bool = False | True
134 data Ordering = LT | EQ | GT
142 (&&) True True = True
148 unpackCString# :: Addr# -> [Char]
149 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
150 unpackAppendCString# :: Addr# -> [Char] -> [Char]
151 unpackCStringUtf8# :: Addr# -> [Char]
152 unpackCString# a = error "urk"
153 unpackFoldrCString# a = error "urk"
154 unpackAppendCString# a = error "urk"
155 unpackCStringUtf8# a = error "urk"
160 %*********************************************************
162 \subsection{Monadic classes @Functor@, @Monad@ }
164 %*********************************************************
167 {- | The 'Functor' class is used for types that can be mapped over.
168 Instances of 'Functor' should satisfy the following laws:
171 > fmap (f . g) == fmap f . fmap g
173 The instances of 'Functor' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
177 class Functor f where
178 fmap :: (a -> b) -> f a -> f b
180 -- | Replace all locations in the input with the same value.
181 -- The default definition is @'fmap' . 'const'@, but this may be
182 -- overridden with a more efficient version.
183 (<$) :: a -> f b -> f a
186 {- | The 'Monad' class defines the basic operations over a /monad/,
187 a concept from a branch of mathematics known as /category theory/.
188 From the perspective of a Haskell programmer, however, it is best to
189 think of a monad as an /abstract datatype/ of actions.
190 Haskell's @do@ expressions provide a convenient syntax for writing
193 Minimal complete definition: '>>=' and 'return'.
195 Instances of 'Monad' should satisfy the following laws:
197 > return a >>= k == k a
199 > m >>= (\x -> k x >>= h) == (m >>= k) >>= h
201 Instances of both 'Monad' and 'Functor' should additionally satisfy the law:
203 > fmap f xs == xs >>= return . f
205 The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
206 defined in the "Prelude" satisfy these laws.
210 -- | Sequentially compose two actions, passing any value produced
211 -- by the first as an argument to the second.
212 (>>=) :: forall a b. m a -> (a -> m b) -> m b
213 -- | Sequentially compose two actions, discarding any value produced
214 -- by the first, like sequencing operators (such as the semicolon)
215 -- in imperative languages.
216 (>>) :: forall a b. m a -> m b -> m b
217 -- Explicit for-alls so that we know what order to
218 -- give type arguments when desugaring
220 -- | Inject a value into the monadic type.
222 -- | Fail with a message. This operation is not part of the
223 -- mathematical definition of a monad, but is invoked on pattern-match
224 -- failure in a @do@ expression.
225 fail :: String -> m a
228 m >> k = m >>= \_ -> k
233 %*********************************************************
235 \subsection{The list type}
237 %*********************************************************
240 instance Functor [] where
243 instance Monad [] where
244 m >>= k = foldr ((++) . k) [] m
245 m >> k = foldr ((++) . (\ _ -> k)) [] m
250 A few list functions that appear here because they are used here.
251 The rest of the prelude list functions are in GHC.List.
253 ----------------------------------------------
254 -- foldr/build/augment
255 ----------------------------------------------
258 -- | 'foldr', applied to a binary operator, a starting value (typically
259 -- the right-identity of the operator), and a list, reduces the list
260 -- using the binary operator, from right to left:
262 -- > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
264 foldr :: (a -> b -> b) -> b -> [a] -> b
266 -- foldr f z (x:xs) = f x (foldr f z xs)
267 {-# INLINE [0] foldr #-}
268 -- Inline only in the final stage, after the foldr/cons rule has had a chance
269 -- Also note that we inline it when it has *two* parameters, which are the
270 -- ones we are keen about specialising!
274 go (y:ys) = y `k` go ys
276 -- | A list producer that can be fused with 'foldr'.
277 -- This function is merely
279 -- > build g = g (:) []
281 -- but GHC's simplifier will transform an expression of the form
282 -- @'foldr' k z ('build' g)@, which may arise after inlining, to @g k z@,
283 -- which avoids producing an intermediate list.
285 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
286 {-# INLINE [1] build #-}
287 -- The INLINE is important, even though build is tiny,
288 -- because it prevents [] getting inlined in the version that
289 -- appears in the interface file. If [] *is* inlined, it
290 -- won't match with [] appearing in rules in an importing module.
292 -- The "1" says to inline in phase 1
296 -- | A list producer that can be fused with 'foldr'.
297 -- This function is merely
299 -- > augment g xs = g (:) xs
301 -- but GHC's simplifier will transform an expression of the form
302 -- @'foldr' k z ('augment' g xs)@, which may arise after inlining, to
303 -- @g k ('foldr' k z xs)@, which avoids producing an intermediate list.
305 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
306 {-# INLINE [1] augment #-}
307 augment g xs = g (:) xs
310 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
311 foldr k z (build g) = g k z
313 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
314 foldr k z (augment g xs) = g k (foldr k z xs)
316 "foldr/id" foldr (:) [] = \x -> x
317 "foldr/app" [1] forall ys. foldr (:) ys = \xs -> xs ++ ys
318 -- Only activate this from phase 1, because that's
319 -- when we disable the rule that expands (++) into foldr
321 -- The foldr/cons rule looks nice, but it can give disastrously
322 -- bloated code when commpiling
323 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
324 -- i.e. when there are very very long literal lists
325 -- So I've disabled it for now. We could have special cases
326 -- for short lists, I suppose.
327 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
329 "foldr/single" forall k z x. foldr k z [x] = k x z
330 "foldr/nil" forall k z. foldr k z [] = z
332 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
333 (h::forall b. (a->b->b) -> b -> b) .
334 augment g (build h) = build (\c n -> g c (h c n))
335 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
336 augment g [] = build g
339 -- This rule is true, but not (I think) useful:
340 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
344 ----------------------------------------------
346 ----------------------------------------------
349 -- | 'map' @f xs@ is the list obtained by applying @f@ to each element
352 -- > map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
353 -- > map f [x1, x2, ...] == [f x1, f x2, ...]
355 map :: (a -> b) -> [a] -> [b]
357 map f (x:xs) = f x : map f xs
360 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
361 {-# INLINE [0] mapFB #-}
362 mapFB c f = \x ys -> c (f x) ys
364 -- The rules for map work like this.
366 -- Up to (but not including) phase 1, we use the "map" rule to
367 -- rewrite all saturated applications of map with its build/fold
368 -- form, hoping for fusion to happen.
369 -- In phase 1 and 0, we switch off that rule, inline build, and
370 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
371 -- thing back into plain map.
373 -- It's important that these two rules aren't both active at once
374 -- (along with build's unfolding) else we'd get an infinite loop
375 -- in the rules. Hence the activation control below.
377 -- The "mapFB" rule optimises compositions of map.
379 -- This same pattern is followed by many other functions:
380 -- e.g. append, filter, iterate, repeat, etc.
383 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
384 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
385 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
390 ----------------------------------------------
392 ----------------------------------------------
394 -- | Append two lists, i.e.,
396 -- > [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
397 -- > [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
399 -- If the first list is not finite, the result is the first list.
401 (++) :: [a] -> [a] -> [a]
403 (++) (x:xs) ys = x : xs ++ ys
406 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
412 %*********************************************************
414 \subsection{Type @Bool@}
416 %*********************************************************
419 -- |'otherwise' is defined as the value 'True'. It helps to make
420 -- guards more readable. eg.
422 -- > f x | x < 0 = ...
423 -- > | otherwise = ...
428 %*********************************************************
430 \subsection{Type @Char@ and @String@}
432 %*********************************************************
435 -- | A 'String' is a list of characters. String constants in Haskell are values
441 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
442 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
443 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
444 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
445 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
446 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
449 -- | The 'Prelude.toEnum' method restricted to the type 'Data.Char.Char'.
452 | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
454 = error ("Prelude.chr: bad argument: " ++ showSignedInt (I# 9#) i "")
456 unsafeChr :: Int -> Char
457 unsafeChr (I# i#) = C# (chr# i#)
459 -- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
461 ord (C# c#) = I# (ord# c#)
464 String equality is used when desugaring pattern-matches against strings.
467 eqString :: String -> String -> Bool
468 eqString [] [] = True
469 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
472 {-# RULES "eqString" (==) = eqString #-}
473 -- eqString also has a BuiltInRule in PrelRules.lhs:
474 -- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
478 %*********************************************************
480 \subsection{Type @Int@}
482 %*********************************************************
485 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
490 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
491 #if WORD_SIZE_IN_BITS == 31
492 minInt = I# (-0x40000000#)
493 maxInt = I# 0x3FFFFFFF#
494 #elif WORD_SIZE_IN_BITS == 32
495 minInt = I# (-0x80000000#)
496 maxInt = I# 0x7FFFFFFF#
498 minInt = I# (-0x8000000000000000#)
499 maxInt = I# 0x7FFFFFFFFFFFFFFF#
502 instance Eq Int where
506 instance Ord Int where
513 compareInt :: Int -> Int -> Ordering
514 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
516 compareInt# :: Int# -> Int# -> Ordering
524 %*********************************************************
526 \subsection{The function type}
528 %*********************************************************
531 -- | Identity function.
535 -- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
536 -- magical strictness property: it is lazy in its first argument,
537 -- even though its semantics is strict.
540 -- Implementation note: its strictness and unfolding are over-ridden
541 -- by the definition in MkId.lhs; in both cases to nothing at all.
542 -- That way, 'lazy' does not get inlined, and the strictness analyser
543 -- sees it as lazy. Then the worker/wrapper phase inlines it.
546 -- Assertion function. This simply ignores its boolean argument.
547 -- The compiler may rewrite it to @('assertError' line)@.
549 -- | If the first argument evaluates to 'True', then the result is the
550 -- second argument. Otherwise an 'AssertionFailed' exception is raised,
551 -- containing a 'String' with the source file and line number of the
554 -- Assertions can normally be turned on or off with a compiler flag
555 -- (for GHC, assertions are normally on unless optimisation is turned on
556 -- with @-O@ or the @-fignore-asserts@
557 -- option is given). When assertions are turned off, the first
558 -- argument to 'assert' is ignored, and the second argument is
559 -- returned as the result.
561 -- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
562 -- but from Template Haskell onwards it's simply
563 -- defined here in Base.lhs
564 assert :: Bool -> a -> a
570 breakpointCond :: Bool -> a -> a
571 breakpointCond _ r = r
573 data Opaque = forall a. O a
575 -- | Constant function.
579 -- | Function composition.
581 -- Make sure it has TWO args only on the left, so that it inlines
582 -- when applied to two functions, even if there is no final argument
583 (.) :: (b -> c) -> (a -> b) -> a -> c
584 (.) f g = \x -> f (g x)
586 -- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
587 flip :: (a -> b -> c) -> b -> a -> c
590 -- | Application operator. This operator is redundant, since ordinary
591 -- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
592 -- low, right-associative binding precedence, so it sometimes allows
593 -- parentheses to be omitted; for example:
595 -- > f $ g $ h x = f (g (h x))
597 -- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
598 -- or @'Data.List.zipWith' ('$') fs xs@.
600 ($) :: (a -> b) -> a -> b
603 -- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
604 until :: (a -> Bool) -> (a -> a) -> a -> a
605 until p f x | p x = x
606 | otherwise = until p f (f x)
608 -- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
609 -- used as an infix operator, and its typing forces its first argument
610 -- (which is usually overloaded) to have the same type as the second.
611 asTypeOf :: a -> a -> a
615 %*********************************************************
617 \subsection{@Functor@ and @Monad@ instances for @IO@}
619 %*********************************************************
622 instance Functor IO where
623 fmap f x = x >>= (return . f)
625 instance Monad IO where
626 {-# INLINE return #-}
629 m >> k = m >>= \ _ -> k
632 fail s = GHC.IO.failIO s
634 returnIO :: a -> IO a
635 returnIO x = IO $ \ s -> (# s, x #)
637 bindIO :: IO a -> (a -> IO b) -> IO b
638 bindIO (IO m) k = IO $ \ s -> case m s of (# new_s, a #) -> unIO (k a) new_s
640 thenIO :: IO a -> IO b -> IO b
641 thenIO (IO m) k = IO $ \ s -> case m s of (# new_s, _ #) -> unIO k new_s
643 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
647 %*********************************************************
649 \subsection{@getTag@}
651 %*********************************************************
653 Returns the 'tag' of a constructor application; this function is used
654 by the deriving code for Eq, Ord and Enum.
656 The primitive dataToTag# requires an evaluated constructor application
657 as its argument, so we provide getTag as a wrapper that performs the
658 evaluation before calling dataToTag#. We could have dataToTag#
659 evaluate its argument, but we prefer to do it this way because (a)
660 dataToTag# can be an inline primop if it doesn't need to do any
661 evaluation, and (b) we want to expose the evaluation to the
662 simplifier, because it might be possible to eliminate the evaluation
663 in the case when the argument is already known to be evaluated.
666 {-# INLINE getTag #-}
668 getTag x = x `seq` dataToTag# x
671 %*********************************************************
673 \subsection{Numeric primops}
675 %*********************************************************
678 divInt# :: Int# -> Int# -> Int#
680 -- Be careful NOT to overflow if we do any additional arithmetic
681 -- on the arguments... the following previous version of this
682 -- code has problems with overflow:
683 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
684 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
685 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
686 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
687 | otherwise = x# `quotInt#` y#
689 modInt# :: Int# -> Int# -> Int#
691 | (x# ># 0#) && (y# <# 0#) ||
692 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
695 !r# = x# `remInt#` y#
698 Definitions of the boxed PrimOps; these will be
699 used in the case of partial applications, etc.
708 {-# INLINE plusInt #-}
709 {-# INLINE minusInt #-}
710 {-# INLINE timesInt #-}
711 {-# INLINE quotInt #-}
712 {-# INLINE remInt #-}
713 {-# INLINE negateInt #-}
715 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt :: Int -> Int -> Int
716 (I# x) `plusInt` (I# y) = I# (x +# y)
717 (I# x) `minusInt` (I# y) = I# (x -# y)
718 (I# x) `timesInt` (I# y) = I# (x *# y)
719 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
720 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
721 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
722 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
725 "x# +# 0#" forall x#. x# +# 0# = x#
726 "0# +# x#" forall x#. 0# +# x# = x#
727 "x# -# 0#" forall x#. x# -# 0# = x#
728 "x# -# x#" forall x#. x# -# x# = 0#
729 "x# *# 0#" forall x#. x# *# 0# = 0#
730 "0# *# x#" forall x#. 0# *# x# = 0#
731 "x# *# 1#" forall x#. x# *# 1# = x#
732 "1# *# x#" forall x#. 1# *# x# = x#
735 negateInt :: Int -> Int
736 negateInt (I# x) = I# (negateInt# x)
738 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
739 (I# x) `gtInt` (I# y) = x ># y
740 (I# x) `geInt` (I# y) = x >=# y
741 (I# x) `eqInt` (I# y) = x ==# y
742 (I# x) `neInt` (I# y) = x /=# y
743 (I# x) `ltInt` (I# y) = x <# y
744 (I# x) `leInt` (I# y) = x <=# y
747 "x# ># x#" forall x#. x# ># x# = False
748 "x# >=# x#" forall x#. x# >=# x# = True
749 "x# ==# x#" forall x#. x# ==# x# = True
750 "x# /=# x#" forall x#. x# /=# x# = False
751 "x# <# x#" forall x#. x# <# x# = False
752 "x# <=# x#" forall x#. x# <=# x# = True
756 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
757 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
758 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
759 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
760 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
761 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
762 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
763 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
764 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
768 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
769 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
770 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
771 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
772 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
773 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
777 We'd like to have more rules, but for example:
779 This gives wrong answer (0) for NaN - NaN (should be NaN):
780 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
782 This gives wrong answer (0) for 0 * NaN (should be NaN):
783 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
785 This gives wrong answer (0) for NaN * 0 (should be NaN):
786 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
788 These are tested by num014.
791 -- Wrappers for the shift operations. The uncheckedShift# family are
792 -- undefined when the amount being shifted by is greater than the size
793 -- in bits of Int#, so these wrappers perform a check and return
794 -- either zero or -1 appropriately.
796 -- Note that these wrappers still produce undefined results when the
797 -- second argument (the shift amount) is negative.
799 -- | Shift the argument left by the specified number of bits
800 -- (which must be non-negative).
801 shiftL# :: Word# -> Int# -> Word#
802 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
803 | otherwise = a `uncheckedShiftL#` b
805 -- | Shift the argument right by the specified number of bits
806 -- (which must be non-negative).
807 shiftRL# :: Word# -> Int# -> Word#
808 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
809 | otherwise = a `uncheckedShiftRL#` b
811 -- | Shift the argument left by the specified number of bits
812 -- (which must be non-negative).
813 iShiftL# :: Int# -> Int# -> Int#
814 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
815 | otherwise = a `uncheckedIShiftL#` b
817 -- | Shift the argument right (signed) by the specified number of bits
818 -- (which must be non-negative).
819 iShiftRA# :: Int# -> Int# -> Int#
820 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
821 | otherwise = a `uncheckedIShiftRA#` b
823 -- | Shift the argument right (unsigned) by the specified number of bits
824 -- (which must be non-negative).
825 iShiftRL# :: Int# -> Int# -> Int#
826 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
827 | otherwise = a `uncheckedIShiftRL#` b
829 #if WORD_SIZE_IN_BITS == 32
831 "narrow32Int#" forall x#. narrow32Int# x# = x#
832 "narrow32Word#" forall x#. narrow32Word# x# = x#
837 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
838 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
843 %********************************************************
845 \subsection{Unpacking C strings}
847 %********************************************************
849 This code is needed for virtually all programs, since it's used for
850 unpacking the strings of error messages.
853 unpackCString# :: Addr# -> [Char]
854 {-# NOINLINE unpackCString# #-}
855 -- There's really no point in inlining this, ever, cos
856 -- the loop doesn't specialise in an interesting
857 -- But it's pretty small, so there's a danger that
858 -- it'll be inlined at every literal, which is a waste
863 | ch `eqChar#` '\0'# = []
864 | otherwise = C# ch : unpack (nh +# 1#)
866 !ch = indexCharOffAddr# addr nh
868 unpackAppendCString# :: Addr# -> [Char] -> [Char]
869 {-# NOINLINE unpackAppendCString# #-}
870 -- See the NOINLINE note on unpackCString#
871 unpackAppendCString# addr rest
875 | ch `eqChar#` '\0'# = rest
876 | otherwise = C# ch : unpack (nh +# 1#)
878 !ch = indexCharOffAddr# addr nh
880 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
882 -- Usually the unpack-list rule turns unpackFoldrCString# into unpackCString#
884 -- It also has a BuiltInRule in PrelRules.lhs:
885 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
886 -- = unpackFoldrCString# "foobaz" c n
888 {-# NOINLINE unpackFoldrCString# #-}
889 -- At one stage I had NOINLINE [0] on the grounds that, unlike
890 -- unpackCString#, there *is* some point in inlining
891 -- unpackFoldrCString#, because we get better code for the
892 -- higher-order function call. BUT there may be a lot of
893 -- literal strings, and making a separate 'unpack' loop for
894 -- each is highly gratuitous. See nofib/real/anna/PrettyPrint.
896 unpackFoldrCString# addr f z
900 | ch `eqChar#` '\0'# = z
901 | otherwise = C# ch `f` unpack (nh +# 1#)
903 !ch = indexCharOffAddr# addr nh
905 unpackCStringUtf8# :: Addr# -> [Char]
906 unpackCStringUtf8# addr
910 | ch `eqChar#` '\0'# = []
911 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
912 | ch `leChar#` '\xDF'# =
913 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
914 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
916 | ch `leChar#` '\xEF'# =
917 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
918 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
919 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
922 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
923 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
924 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
925 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
928 !ch = indexCharOffAddr# addr nh
930 unpackNBytes# :: Addr# -> Int# -> [Char]
931 unpackNBytes# _addr 0# = []
932 unpackNBytes# addr len# = unpack [] (len# -# 1#)
937 case indexCharOffAddr# addr i# of
938 ch -> unpack (C# ch : acc) (i# -# 1#)
941 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
942 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
943 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
945 -- There's a built-in rule (in PrelRules.lhs) for
946 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
953 -- | A special argument for the 'Control.Monad.ST.ST' type constructor,
954 -- indexing a state embedded in the 'Prelude.IO' monad by
955 -- 'Control.Monad.ST.stToIO'.