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 {-# OPTIONS_GHC -fno-warn-orphans #-}
67 {-# OPTIONS_HADDOCK hide #-}
68 -----------------------------------------------------------------------------
71 -- Copyright : (c) The University of Glasgow, 1992-2002
72 -- License : see libraries/base/LICENSE
74 -- Maintainer : cvs-ghc@haskell.org
75 -- Stability : internal
76 -- Portability : non-portable (GHC extensions)
78 -- Basic data types and classes.
80 -----------------------------------------------------------------------------
93 module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
94 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'
174 defined in the "Prelude" satisfy these laws.
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
440 {-| The character type 'Char' is an enumeration whose values represent
441 Unicode (or equivalently ISO\/IEC 10646) characters
442 (see <http://www.unicode.org/> for details).
443 This set extends the ISO 8859-1 (Latin-1) character set
444 (the first 256 charachers), which is itself an extension of the ASCII
445 character set (the first 128 characters).
446 A character literal in Haskell has type 'Char'.
448 To convert a 'Char' to or from the corresponding 'Int' value defined
449 by Unicode, use 'Prelude.toEnum' and 'Prelude.fromEnum' from the
450 'Prelude.Enum' class respectively (or equivalently 'ord' and 'chr').
454 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
455 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
456 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
457 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
458 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
459 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
462 -- | The 'Prelude.toEnum' method restricted to the type 'Data.Char.Char'.
465 | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
467 = error ("Prelude.chr: bad argument: " ++ showSignedInt (I# 9#) i "")
469 unsafeChr :: Int -> Char
470 unsafeChr (I# i#) = C# (chr# i#)
472 -- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
474 ord (C# c#) = I# (ord# c#)
477 String equality is used when desugaring pattern-matches against strings.
480 eqString :: String -> String -> Bool
481 eqString [] [] = True
482 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
485 {-# RULES "eqString" (==) = eqString #-}
486 -- eqString also has a BuiltInRule in PrelRules.lhs:
487 -- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
491 %*********************************************************
493 \subsection{Type @Int@}
495 %*********************************************************
498 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
503 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
504 #if WORD_SIZE_IN_BITS == 31
505 minInt = I# (-0x40000000#)
506 maxInt = I# 0x3FFFFFFF#
507 #elif WORD_SIZE_IN_BITS == 32
508 minInt = I# (-0x80000000#)
509 maxInt = I# 0x7FFFFFFF#
511 minInt = I# (-0x8000000000000000#)
512 maxInt = I# 0x7FFFFFFFFFFFFFFF#
515 instance Eq Int where
519 instance Ord Int where
526 compareInt :: Int -> Int -> Ordering
527 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
529 compareInt# :: Int# -> Int# -> Ordering
537 %*********************************************************
539 \subsection{The function type}
541 %*********************************************************
544 -- | Identity function.
548 -- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
549 -- magical strictness property: it is lazy in its first argument,
550 -- even though its semantics is strict.
553 -- Implementation note: its strictness and unfolding are over-ridden
554 -- by the definition in MkId.lhs; in both cases to nothing at all.
555 -- That way, 'lazy' does not get inlined, and the strictness analyser
556 -- sees it as lazy. Then the worker/wrapper phase inlines it.
559 -- Assertion function. This simply ignores its boolean argument.
560 -- The compiler may rewrite it to @('assertError' line)@.
562 -- | If the first argument evaluates to 'True', then the result is the
563 -- second argument. Otherwise an 'AssertionFailed' exception is raised,
564 -- containing a 'String' with the source file and line number of the
567 -- Assertions can normally be turned on or off with a compiler flag
568 -- (for GHC, assertions are normally on unless optimisation is turned on
569 -- with @-O@ or the @-fignore-asserts@
570 -- option is given). When assertions are turned off, the first
571 -- argument to 'assert' is ignored, and the second argument is
572 -- returned as the result.
574 -- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
575 -- but from Template Haskell onwards it's simply
576 -- defined here in Base.lhs
577 assert :: Bool -> a -> a
583 breakpointCond :: Bool -> a -> a
584 breakpointCond _ r = r
586 data Opaque = forall a. O a
588 -- | Constant function.
592 -- | Function composition.
594 -- Make sure it has TWO args only on the left, so that it inlines
595 -- when applied to two functions, even if there is no final argument
596 (.) :: (b -> c) -> (a -> b) -> a -> c
597 (.) f g = \x -> f (g x)
599 -- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
600 flip :: (a -> b -> c) -> b -> a -> c
603 -- | Application operator. This operator is redundant, since ordinary
604 -- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
605 -- low, right-associative binding precedence, so it sometimes allows
606 -- parentheses to be omitted; for example:
608 -- > f $ g $ h x = f (g (h x))
610 -- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
611 -- or @'Data.List.zipWith' ('$') fs xs@.
613 ($) :: (a -> b) -> a -> b
616 -- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
617 until :: (a -> Bool) -> (a -> a) -> a -> a
618 until p f x | p x = x
619 | otherwise = until p f (f x)
621 -- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
622 -- used as an infix operator, and its typing forces its first argument
623 -- (which is usually overloaded) to have the same type as the second.
624 asTypeOf :: a -> a -> a
628 %*********************************************************
630 \subsection{@Functor@ and @Monad@ instances for @IO@}
632 %*********************************************************
635 instance Functor IO where
636 fmap f x = x >>= (return . f)
638 instance Monad IO where
639 {-# INLINE return #-}
642 m >> k = m >>= \ _ -> k
645 fail s = GHC.IO.failIO s
647 returnIO :: a -> IO a
648 returnIO x = IO $ \ s -> (# s, x #)
650 bindIO :: IO a -> (a -> IO b) -> IO b
651 bindIO (IO m) k = IO $ \ s -> case m s of (# new_s, a #) -> unIO (k a) new_s
653 thenIO :: IO a -> IO b -> IO b
654 thenIO (IO m) k = IO $ \ s -> case m s of (# new_s, _ #) -> unIO k new_s
656 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
660 %*********************************************************
662 \subsection{@getTag@}
664 %*********************************************************
666 Returns the 'tag' of a constructor application; this function is used
667 by the deriving code for Eq, Ord and Enum.
669 The primitive dataToTag# requires an evaluated constructor application
670 as its argument, so we provide getTag as a wrapper that performs the
671 evaluation before calling dataToTag#. We could have dataToTag#
672 evaluate its argument, but we prefer to do it this way because (a)
673 dataToTag# can be an inline primop if it doesn't need to do any
674 evaluation, and (b) we want to expose the evaluation to the
675 simplifier, because it might be possible to eliminate the evaluation
676 in the case when the argument is already known to be evaluated.
679 {-# INLINE getTag #-}
681 getTag x = x `seq` dataToTag# x
684 %*********************************************************
686 \subsection{Numeric primops}
688 %*********************************************************
691 divInt# :: Int# -> Int# -> Int#
693 -- Be careful NOT to overflow if we do any additional arithmetic
694 -- on the arguments... the following previous version of this
695 -- code has problems with overflow:
696 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
697 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
698 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
699 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
700 | otherwise = x# `quotInt#` y#
702 modInt# :: Int# -> Int# -> Int#
704 | (x# ># 0#) && (y# <# 0#) ||
705 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
708 !r# = x# `remInt#` y#
711 Definitions of the boxed PrimOps; these will be
712 used in the case of partial applications, etc.
721 {-# INLINE plusInt #-}
722 {-# INLINE minusInt #-}
723 {-# INLINE timesInt #-}
724 {-# INLINE quotInt #-}
725 {-# INLINE remInt #-}
726 {-# INLINE negateInt #-}
728 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt :: Int -> Int -> Int
729 (I# x) `plusInt` (I# y) = I# (x +# y)
730 (I# x) `minusInt` (I# y) = I# (x -# y)
731 (I# x) `timesInt` (I# y) = I# (x *# y)
732 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
733 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
734 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
735 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
738 "x# +# 0#" forall x#. x# +# 0# = x#
739 "0# +# x#" forall x#. 0# +# x# = x#
740 "x# -# 0#" forall x#. x# -# 0# = x#
741 "x# -# x#" forall x#. x# -# x# = 0#
742 "x# *# 0#" forall x#. x# *# 0# = 0#
743 "0# *# x#" forall x#. 0# *# x# = 0#
744 "x# *# 1#" forall x#. x# *# 1# = x#
745 "1# *# x#" forall x#. 1# *# x# = x#
748 negateInt :: Int -> Int
749 negateInt (I# x) = I# (negateInt# x)
751 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
752 (I# x) `gtInt` (I# y) = x ># y
753 (I# x) `geInt` (I# y) = x >=# y
754 (I# x) `eqInt` (I# y) = x ==# y
755 (I# x) `neInt` (I# y) = x /=# y
756 (I# x) `ltInt` (I# y) = x <# y
757 (I# x) `leInt` (I# y) = x <=# y
760 "x# ># x#" forall x#. x# ># x# = False
761 "x# >=# x#" forall x#. x# >=# x# = True
762 "x# ==# x#" forall x#. x# ==# x# = True
763 "x# /=# x#" forall x#. x# /=# x# = False
764 "x# <# x#" forall x#. x# <# x# = False
765 "x# <=# x#" forall x#. x# <=# x# = True
769 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
770 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
771 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
772 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
773 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
774 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
775 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
776 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
777 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
781 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
782 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
783 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
784 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
785 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
786 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
790 We'd like to have more rules, but for example:
792 This gives wrong answer (0) for NaN - NaN (should be NaN):
793 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
795 This gives wrong answer (0) for 0 * NaN (should be NaN):
796 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
798 This gives wrong answer (0) for NaN * 0 (should be NaN):
799 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
801 These are tested by num014.
804 -- Wrappers for the shift operations. The uncheckedShift# family are
805 -- undefined when the amount being shifted by is greater than the size
806 -- in bits of Int#, so these wrappers perform a check and return
807 -- either zero or -1 appropriately.
809 -- Note that these wrappers still produce undefined results when the
810 -- second argument (the shift amount) is negative.
812 -- | Shift the argument left by the specified number of bits
813 -- (which must be non-negative).
814 shiftL# :: Word# -> Int# -> Word#
815 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
816 | otherwise = a `uncheckedShiftL#` b
818 -- | Shift the argument right by the specified number of bits
819 -- (which must be non-negative).
820 shiftRL# :: Word# -> Int# -> Word#
821 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
822 | otherwise = a `uncheckedShiftRL#` b
824 -- | Shift the argument left by the specified number of bits
825 -- (which must be non-negative).
826 iShiftL# :: Int# -> Int# -> Int#
827 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
828 | otherwise = a `uncheckedIShiftL#` b
830 -- | Shift the argument right (signed) by the specified number of bits
831 -- (which must be non-negative).
832 iShiftRA# :: Int# -> Int# -> Int#
833 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
834 | otherwise = a `uncheckedIShiftRA#` b
836 -- | Shift the argument right (unsigned) by the specified number of bits
837 -- (which must be non-negative).
838 iShiftRL# :: Int# -> Int# -> Int#
839 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
840 | otherwise = a `uncheckedIShiftRL#` b
842 #if WORD_SIZE_IN_BITS == 32
844 "narrow32Int#" forall x#. narrow32Int# x# = x#
845 "narrow32Word#" forall x#. narrow32Word# x# = x#
850 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
851 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
856 %********************************************************
858 \subsection{Unpacking C strings}
860 %********************************************************
862 This code is needed for virtually all programs, since it's used for
863 unpacking the strings of error messages.
866 unpackCString# :: Addr# -> [Char]
867 {-# NOINLINE unpackCString# #-}
868 -- There's really no point in inlining this, ever, cos
869 -- the loop doesn't specialise in an interesting
870 -- But it's pretty small, so there's a danger that
871 -- it'll be inlined at every literal, which is a waste
876 | ch `eqChar#` '\0'# = []
877 | otherwise = C# ch : unpack (nh +# 1#)
879 !ch = indexCharOffAddr# addr nh
881 unpackAppendCString# :: Addr# -> [Char] -> [Char]
882 {-# NOINLINE unpackAppendCString# #-}
883 -- See the NOINLINE note on unpackCString#
884 unpackAppendCString# addr rest
888 | ch `eqChar#` '\0'# = rest
889 | otherwise = C# ch : unpack (nh +# 1#)
891 !ch = indexCharOffAddr# addr nh
893 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
895 -- Usually the unpack-list rule turns unpackFoldrCString# into unpackCString#
897 -- It also has a BuiltInRule in PrelRules.lhs:
898 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
899 -- = unpackFoldrCString# "foobaz" c n
901 {-# NOINLINE unpackFoldrCString# #-}
902 -- At one stage I had NOINLINE [0] on the grounds that, unlike
903 -- unpackCString#, there *is* some point in inlining
904 -- unpackFoldrCString#, because we get better code for the
905 -- higher-order function call. BUT there may be a lot of
906 -- literal strings, and making a separate 'unpack' loop for
907 -- each is highly gratuitous. See nofib/real/anna/PrettyPrint.
909 unpackFoldrCString# addr f z
913 | ch `eqChar#` '\0'# = z
914 | otherwise = C# ch `f` unpack (nh +# 1#)
916 !ch = indexCharOffAddr# addr nh
918 unpackCStringUtf8# :: Addr# -> [Char]
919 unpackCStringUtf8# addr
923 | ch `eqChar#` '\0'# = []
924 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
925 | ch `leChar#` '\xDF'# =
926 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
927 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
929 | ch `leChar#` '\xEF'# =
930 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
931 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
932 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
935 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
936 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
937 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
938 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
941 !ch = indexCharOffAddr# addr nh
943 unpackNBytes# :: Addr# -> Int# -> [Char]
944 unpackNBytes# _addr 0# = []
945 unpackNBytes# addr len# = unpack [] (len# -# 1#)
950 case indexCharOffAddr# addr i# of
951 ch -> unpack (C# ch : acc) (i# -# 1#)
954 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
955 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
956 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
958 -- There's a built-in rule (in PrelRules.lhs) for
959 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
966 -- | A special argument for the 'Control.Monad.ST.ST' type constructor,
967 -- indexing a state embedded in the 'Prelude.IO' monad by
968 -- 'Control.Monad.ST.stToIO'.