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 -----------------------------------------------------------------------------
95 module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
96 module GHC.Err -- of people having to import it explicitly
106 import {-# SOURCE #-} GHC.Show
107 import {-# SOURCE #-} GHC.Err
108 import {-# SOURCE #-} GHC.IO (failIO)
110 -- These two are not strictly speaking required by this module, but they are
111 -- implicit dependencies whenever () or tuples are mentioned, so adding them
112 -- as imports here helps to get the dependencies right in the new build system.
122 default () -- Double isn't available yet
126 %*********************************************************
128 \subsection{DEBUGGING STUFF}
129 %* (for use when compiling GHC.Base itself doesn't work)
131 %*********************************************************
135 data Bool = False | True
136 data Ordering = LT | EQ | GT
144 (&&) True True = True
150 unpackCString# :: Addr# -> [Char]
151 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
152 unpackAppendCString# :: Addr# -> [Char] -> [Char]
153 unpackCStringUtf8# :: Addr# -> [Char]
154 unpackCString# a = error "urk"
155 unpackFoldrCString# a = error "urk"
156 unpackAppendCString# a = error "urk"
157 unpackCStringUtf8# a = error "urk"
162 %*********************************************************
164 \subsection{Monadic classes @Functor@, @Monad@ }
166 %*********************************************************
169 {- | The 'Functor' class is used for types that can be mapped over.
170 Instances of 'Functor' should satisfy the following laws:
173 > fmap (f . g) == fmap f . fmap g
175 The instances of 'Functor' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
176 defined in the "Prelude" satisfy these laws.
179 class Functor f where
180 fmap :: (a -> b) -> f a -> f b
182 -- | Replace all locations in the input with the same value.
183 -- The default definition is @'fmap' . 'const'@, but this may be
184 -- overridden with a more efficient version.
185 (<$) :: a -> f b -> f a
188 {- | The 'Monad' class defines the basic operations over a /monad/,
189 a concept from a branch of mathematics known as /category theory/.
190 From the perspective of a Haskell programmer, however, it is best to
191 think of a monad as an /abstract datatype/ of actions.
192 Haskell's @do@ expressions provide a convenient syntax for writing
195 Minimal complete definition: '>>=' and 'return'.
197 Instances of 'Monad' should satisfy the following laws:
199 > return a >>= k == k a
201 > m >>= (\x -> k x >>= h) == (m >>= k) >>= h
203 Instances of both 'Monad' and 'Functor' should additionally satisfy the law:
205 > fmap f xs == xs >>= return . f
207 The instances of 'Monad' for lists, 'Data.Maybe.Maybe' and 'System.IO.IO'
208 defined in the "Prelude" satisfy these laws.
212 -- | Sequentially compose two actions, passing any value produced
213 -- by the first as an argument to the second.
214 (>>=) :: forall a b. m a -> (a -> m b) -> m b
215 -- | Sequentially compose two actions, discarding any value produced
216 -- by the first, like sequencing operators (such as the semicolon)
217 -- in imperative languages.
218 (>>) :: forall a b. m a -> m b -> m b
219 -- Explicit for-alls so that we know what order to
220 -- give type arguments when desugaring
222 -- | Inject a value into the monadic type.
224 -- | Fail with a message. This operation is not part of the
225 -- mathematical definition of a monad, but is invoked on pattern-match
226 -- failure in a @do@ expression.
227 fail :: String -> m a
230 m >> k = m >>= \_ -> k
235 %*********************************************************
237 \subsection{The list type}
239 %*********************************************************
242 instance Functor [] where
245 instance Monad [] where
246 m >>= k = foldr ((++) . k) [] m
247 m >> k = foldr ((++) . (\ _ -> k)) [] m
252 A few list functions that appear here because they are used here.
253 The rest of the prelude list functions are in GHC.List.
255 ----------------------------------------------
256 -- foldr/build/augment
257 ----------------------------------------------
260 -- | 'foldr', applied to a binary operator, a starting value (typically
261 -- the right-identity of the operator), and a list, reduces the list
262 -- using the binary operator, from right to left:
264 -- > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
266 foldr :: (a -> b -> b) -> b -> [a] -> b
268 -- foldr f z (x:xs) = f x (foldr f z xs)
269 {-# INLINE [0] foldr #-}
270 -- Inline only in the final stage, after the foldr/cons rule has had a chance
271 -- Also note that we inline it when it has *two* parameters, which are the
272 -- ones we are keen about specialising!
276 go (y:ys) = y `k` go ys
278 -- | A list producer that can be fused with 'foldr'.
279 -- This function is merely
281 -- > build g = g (:) []
283 -- but GHC's simplifier will transform an expression of the form
284 -- @'foldr' k z ('build' g)@, which may arise after inlining, to @g k z@,
285 -- which avoids producing an intermediate list.
287 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
288 {-# INLINE [1] build #-}
289 -- The INLINE is important, even though build is tiny,
290 -- because it prevents [] getting inlined in the version that
291 -- appears in the interface file. If [] *is* inlined, it
292 -- won't match with [] appearing in rules in an importing module.
294 -- The "1" says to inline in phase 1
298 -- | A list producer that can be fused with 'foldr'.
299 -- This function is merely
301 -- > augment g xs = g (:) xs
303 -- but GHC's simplifier will transform an expression of the form
304 -- @'foldr' k z ('augment' g xs)@, which may arise after inlining, to
305 -- @g k ('foldr' k z xs)@, which avoids producing an intermediate list.
307 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
308 {-# INLINE [1] augment #-}
309 augment g xs = g (:) xs
312 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
313 foldr k z (build g) = g k z
315 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
316 foldr k z (augment g xs) = g k (foldr k z xs)
318 "foldr/id" foldr (:) [] = \x -> x
319 "foldr/app" [1] forall ys. foldr (:) ys = \xs -> xs ++ ys
320 -- Only activate this from phase 1, because that's
321 -- when we disable the rule that expands (++) into foldr
323 -- The foldr/cons rule looks nice, but it can give disastrously
324 -- bloated code when commpiling
325 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
326 -- i.e. when there are very very long literal lists
327 -- So I've disabled it for now. We could have special cases
328 -- for short lists, I suppose.
329 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
331 "foldr/single" forall k z x. foldr k z [x] = k x z
332 "foldr/nil" forall k z. foldr k z [] = z
334 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
335 (h::forall b. (a->b->b) -> b -> b) .
336 augment g (build h) = build (\c n -> g c (h c n))
337 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
338 augment g [] = build g
341 -- This rule is true, but not (I think) useful:
342 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
346 ----------------------------------------------
348 ----------------------------------------------
351 -- | 'map' @f xs@ is the list obtained by applying @f@ to each element
354 -- > map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
355 -- > map f [x1, x2, ...] == [f x1, f x2, ...]
357 map :: (a -> b) -> [a] -> [b]
359 map f (x:xs) = f x : map f xs
362 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
363 {-# INLINE [0] mapFB #-}
364 mapFB c f = \x ys -> c (f x) ys
366 -- The rules for map work like this.
368 -- Up to (but not including) phase 1, we use the "map" rule to
369 -- rewrite all saturated applications of map with its build/fold
370 -- form, hoping for fusion to happen.
371 -- In phase 1 and 0, we switch off that rule, inline build, and
372 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
373 -- thing back into plain map.
375 -- It's important that these two rules aren't both active at once
376 -- (along with build's unfolding) else we'd get an infinite loop
377 -- in the rules. Hence the activation control below.
379 -- The "mapFB" rule optimises compositions of map.
381 -- This same pattern is followed by many other functions:
382 -- e.g. append, filter, iterate, repeat, etc.
385 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
386 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
387 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
392 ----------------------------------------------
394 ----------------------------------------------
396 -- | Append two lists, i.e.,
398 -- > [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
399 -- > [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
401 -- If the first list is not finite, the result is the first list.
403 (++) :: [a] -> [a] -> [a]
405 (++) (x:xs) ys = x : xs ++ ys
408 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
414 %*********************************************************
416 \subsection{Type @Bool@}
418 %*********************************************************
421 -- |'otherwise' is defined as the value 'True'. It helps to make
422 -- guards more readable. eg.
424 -- > f x | x < 0 = ...
425 -- > | otherwise = ...
430 %*********************************************************
432 \subsection{Type @Char@ and @String@}
434 %*********************************************************
437 -- | A 'String' is a list of characters. String constants in Haskell are values
442 {-| The character type 'Char' is an enumeration whose values represent
443 Unicode (or equivalently ISO\/IEC 10646) characters
444 (see <http://www.unicode.org/> for details).
445 This set extends the ISO 8859-1 (Latin-1) character set
446 (the first 256 charachers), which is itself an extension of the ASCII
447 character set (the first 128 characters).
448 A character literal in Haskell has type 'Char'.
450 To convert a 'Char' to or from the corresponding 'Int' value defined
451 by Unicode, use 'Prelude.toEnum' and 'Prelude.fromEnum' from the
452 'Prelude.Enum' class respectively (or equivalently 'ord' and 'chr').
456 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
457 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
458 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
459 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
460 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
461 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
464 -- | The 'Prelude.toEnum' method restricted to the type 'Data.Char.Char'.
467 | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
469 = error ("Prelude.chr: bad argument: " ++ showSignedInt (I# 9#) i "")
471 unsafeChr :: Int -> Char
472 unsafeChr (I# i#) = C# (chr# i#)
474 -- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
476 ord (C# c#) = I# (ord# c#)
479 String equality is used when desugaring pattern-matches against strings.
482 eqString :: String -> String -> Bool
483 eqString [] [] = True
484 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
487 {-# RULES "eqString" (==) = eqString #-}
488 -- eqString also has a BuiltInRule in PrelRules.lhs:
489 -- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
493 %*********************************************************
495 \subsection{Type @Int@}
497 %*********************************************************
500 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
505 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
506 #if WORD_SIZE_IN_BITS == 31
507 minInt = I# (-0x40000000#)
508 maxInt = I# 0x3FFFFFFF#
509 #elif WORD_SIZE_IN_BITS == 32
510 minInt = I# (-0x80000000#)
511 maxInt = I# 0x7FFFFFFF#
513 minInt = I# (-0x8000000000000000#)
514 maxInt = I# 0x7FFFFFFFFFFFFFFF#
517 instance Eq Int where
521 instance Ord Int where
528 compareInt :: Int -> Int -> Ordering
529 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
531 compareInt# :: Int# -> Int# -> Ordering
539 %*********************************************************
541 \subsection{The function type}
543 %*********************************************************
546 -- | Identity function.
550 -- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
551 -- magical strictness property: it is lazy in its first argument,
552 -- even though its semantics is strict.
555 -- Implementation note: its strictness and unfolding are over-ridden
556 -- by the definition in MkId.lhs; in both cases to nothing at all.
557 -- That way, 'lazy' does not get inlined, and the strictness analyser
558 -- sees it as lazy. Then the worker/wrapper phase inlines it.
561 -- Assertion function. This simply ignores its boolean argument.
562 -- The compiler may rewrite it to @('assertError' line)@.
564 -- | If the first argument evaluates to 'True', then the result is the
565 -- second argument. Otherwise an 'AssertionFailed' exception is raised,
566 -- containing a 'String' with the source file and line number of the
569 -- Assertions can normally be turned on or off with a compiler flag
570 -- (for GHC, assertions are normally on unless optimisation is turned on
571 -- with @-O@ or the @-fignore-asserts@
572 -- option is given). When assertions are turned off, the first
573 -- argument to 'assert' is ignored, and the second argument is
574 -- returned as the result.
576 -- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
577 -- but from Template Haskell onwards it's simply
578 -- defined here in Base.lhs
579 assert :: Bool -> a -> a
585 breakpointCond :: Bool -> a -> a
586 breakpointCond _ r = r
588 data Opaque = forall a. O a
590 -- | Constant function.
594 -- | Function composition.
596 -- Make sure it has TWO args only on the left, so that it inlines
597 -- when applied to two functions, even if there is no final argument
598 (.) :: (b -> c) -> (a -> b) -> a -> c
599 (.) f g = \x -> f (g x)
601 -- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
602 flip :: (a -> b -> c) -> b -> a -> c
605 -- | Application operator. This operator is redundant, since ordinary
606 -- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
607 -- low, right-associative binding precedence, so it sometimes allows
608 -- parentheses to be omitted; for example:
610 -- > f $ g $ h x = f (g (h x))
612 -- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
613 -- or @'Data.List.zipWith' ('$') fs xs@.
615 ($) :: (a -> b) -> a -> b
618 -- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
619 until :: (a -> Bool) -> (a -> a) -> a -> a
620 until p f x | p x = x
621 | otherwise = until p f (f x)
623 -- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
624 -- used as an infix operator, and its typing forces its first argument
625 -- (which is usually overloaded) to have the same type as the second.
626 asTypeOf :: a -> a -> a
630 %*********************************************************
632 \subsection{@Functor@ and @Monad@ instances for @IO@}
634 %*********************************************************
637 instance Functor IO where
638 fmap f x = x >>= (return . f)
640 instance Monad IO where
641 {-# INLINE return #-}
644 m >> k = m >>= \ _ -> k
647 fail s = GHC.IO.failIO s
649 returnIO :: a -> IO a
650 returnIO x = IO $ \ s -> (# s, x #)
652 bindIO :: IO a -> (a -> IO b) -> IO b
653 bindIO (IO m) k = IO $ \ s -> case m s of (# new_s, a #) -> unIO (k a) new_s
655 thenIO :: IO a -> IO b -> IO b
656 thenIO (IO m) k = IO $ \ s -> case m s of (# new_s, _ #) -> unIO k new_s
658 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
662 %*********************************************************
664 \subsection{@getTag@}
666 %*********************************************************
668 Returns the 'tag' of a constructor application; this function is used
669 by the deriving code for Eq, Ord and Enum.
671 The primitive dataToTag# requires an evaluated constructor application
672 as its argument, so we provide getTag as a wrapper that performs the
673 evaluation before calling dataToTag#. We could have dataToTag#
674 evaluate its argument, but we prefer to do it this way because (a)
675 dataToTag# can be an inline primop if it doesn't need to do any
676 evaluation, and (b) we want to expose the evaluation to the
677 simplifier, because it might be possible to eliminate the evaluation
678 in the case when the argument is already known to be evaluated.
681 {-# INLINE getTag #-}
683 getTag x = x `seq` dataToTag# x
686 %*********************************************************
688 \subsection{Numeric primops}
690 %*********************************************************
693 divInt# :: Int# -> Int# -> Int#
695 -- Be careful NOT to overflow if we do any additional arithmetic
696 -- on the arguments... the following previous version of this
697 -- code has problems with overflow:
698 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
699 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
700 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
701 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
702 | otherwise = x# `quotInt#` y#
704 modInt# :: Int# -> Int# -> Int#
706 | (x# ># 0#) && (y# <# 0#) ||
707 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
710 !r# = x# `remInt#` y#
713 Definitions of the boxed PrimOps; these will be
714 used in the case of partial applications, etc.
723 {-# INLINE plusInt #-}
724 {-# INLINE minusInt #-}
725 {-# INLINE timesInt #-}
726 {-# INLINE quotInt #-}
727 {-# INLINE remInt #-}
728 {-# INLINE negateInt #-}
730 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt :: Int -> Int -> Int
731 (I# x) `plusInt` (I# y) = I# (x +# y)
732 (I# x) `minusInt` (I# y) = I# (x -# y)
733 (I# x) `timesInt` (I# y) = I# (x *# y)
734 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
735 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
736 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
737 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
740 "x# +# 0#" forall x#. x# +# 0# = x#
741 "0# +# x#" forall x#. 0# +# x# = x#
742 "x# -# 0#" forall x#. x# -# 0# = x#
743 "x# -# x#" forall x#. x# -# x# = 0#
744 "x# *# 0#" forall x#. x# *# 0# = 0#
745 "0# *# x#" forall x#. 0# *# x# = 0#
746 "x# *# 1#" forall x#. x# *# 1# = x#
747 "1# *# x#" forall x#. 1# *# x# = x#
750 negateInt :: Int -> Int
751 negateInt (I# x) = I# (negateInt# x)
753 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
754 (I# x) `gtInt` (I# y) = x ># y
755 (I# x) `geInt` (I# y) = x >=# y
756 (I# x) `eqInt` (I# y) = x ==# y
757 (I# x) `neInt` (I# y) = x /=# y
758 (I# x) `ltInt` (I# y) = x <# y
759 (I# x) `leInt` (I# y) = x <=# y
762 "x# ># x#" forall x#. x# ># x# = False
763 "x# >=# x#" forall x#. x# >=# x# = True
764 "x# ==# x#" forall x#. x# ==# x# = True
765 "x# /=# x#" forall x#. x# /=# x# = False
766 "x# <# x#" forall x#. x# <# x# = False
767 "x# <=# x#" forall x#. x# <=# x# = True
771 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
772 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
773 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
774 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
775 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
776 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
777 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
778 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
779 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
783 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
784 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
785 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
786 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
787 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
788 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
792 We'd like to have more rules, but for example:
794 This gives wrong answer (0) for NaN - NaN (should be NaN):
795 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
797 This gives wrong answer (0) for 0 * NaN (should be NaN):
798 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
800 This gives wrong answer (0) for NaN * 0 (should be NaN):
801 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
803 These are tested by num014.
806 -- Wrappers for the shift operations. The uncheckedShift# family are
807 -- undefined when the amount being shifted by is greater than the size
808 -- in bits of Int#, so these wrappers perform a check and return
809 -- either zero or -1 appropriately.
811 -- Note that these wrappers still produce undefined results when the
812 -- second argument (the shift amount) is negative.
814 -- | Shift the argument left by the specified number of bits
815 -- (which must be non-negative).
816 shiftL# :: Word# -> Int# -> Word#
817 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
818 | otherwise = a `uncheckedShiftL#` b
820 -- | Shift the argument right by the specified number of bits
821 -- (which must be non-negative).
822 shiftRL# :: Word# -> Int# -> Word#
823 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
824 | otherwise = a `uncheckedShiftRL#` b
826 -- | Shift the argument left by the specified number of bits
827 -- (which must be non-negative).
828 iShiftL# :: Int# -> Int# -> Int#
829 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
830 | otherwise = a `uncheckedIShiftL#` b
832 -- | Shift the argument right (signed) by the specified number of bits
833 -- (which must be non-negative).
834 iShiftRA# :: Int# -> Int# -> Int#
835 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
836 | otherwise = a `uncheckedIShiftRA#` b
838 -- | Shift the argument right (unsigned) by the specified number of bits
839 -- (which must be non-negative).
840 iShiftRL# :: Int# -> Int# -> Int#
841 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
842 | otherwise = a `uncheckedIShiftRL#` b
844 #if WORD_SIZE_IN_BITS == 32
846 "narrow32Int#" forall x#. narrow32Int# x# = x#
847 "narrow32Word#" forall x#. narrow32Word# x# = x#
852 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
853 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
858 %********************************************************
860 \subsection{Unpacking C strings}
862 %********************************************************
864 This code is needed for virtually all programs, since it's used for
865 unpacking the strings of error messages.
868 unpackCString# :: Addr# -> [Char]
869 {-# NOINLINE unpackCString# #-}
870 -- There's really no point in inlining this, ever, cos
871 -- the loop doesn't specialise in an interesting
872 -- But it's pretty small, so there's a danger that
873 -- it'll be inlined at every literal, which is a waste
878 | ch `eqChar#` '\0'# = []
879 | otherwise = C# ch : unpack (nh +# 1#)
881 !ch = indexCharOffAddr# addr nh
883 unpackAppendCString# :: Addr# -> [Char] -> [Char]
884 {-# NOINLINE unpackAppendCString# #-}
885 -- See the NOINLINE note on unpackCString#
886 unpackAppendCString# addr rest
890 | ch `eqChar#` '\0'# = rest
891 | otherwise = C# ch : unpack (nh +# 1#)
893 !ch = indexCharOffAddr# addr nh
895 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
897 -- Usually the unpack-list rule turns unpackFoldrCString# into unpackCString#
899 -- It also has a BuiltInRule in PrelRules.lhs:
900 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
901 -- = unpackFoldrCString# "foobaz" c n
903 {-# NOINLINE unpackFoldrCString# #-}
904 -- At one stage I had NOINLINE [0] on the grounds that, unlike
905 -- unpackCString#, there *is* some point in inlining
906 -- unpackFoldrCString#, because we get better code for the
907 -- higher-order function call. BUT there may be a lot of
908 -- literal strings, and making a separate 'unpack' loop for
909 -- each is highly gratuitous. See nofib/real/anna/PrettyPrint.
911 unpackFoldrCString# addr f z
915 | ch `eqChar#` '\0'# = z
916 | otherwise = C# ch `f` unpack (nh +# 1#)
918 !ch = indexCharOffAddr# addr nh
920 unpackCStringUtf8# :: Addr# -> [Char]
921 unpackCStringUtf8# addr
925 | ch `eqChar#` '\0'# = []
926 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
927 | ch `leChar#` '\xDF'# =
928 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
929 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
931 | ch `leChar#` '\xEF'# =
932 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
933 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
934 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
937 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
938 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
939 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
940 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
943 !ch = indexCharOffAddr# addr nh
945 unpackNBytes# :: Addr# -> Int# -> [Char]
946 unpackNBytes# _addr 0# = []
947 unpackNBytes# addr len# = unpack [] (len# -# 1#)
952 case indexCharOffAddr# addr i# of
953 ch -> unpack (C# ch : acc) (i# -# 1#)
956 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
957 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
958 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
960 -- There's a built-in rule (in PrelRules.lhs) for
961 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
968 -- | A special argument for the 'Control.Monad.ST.ST' type constructor,
969 -- indexing a state embedded in the 'Prelude.IO' monad by
970 -- 'Control.Monad.ST.stToIO'.