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 -- do explicitly: deriving (Eq, Ord)
241 -- to avoid weird names like con2tag_[]#
243 instance (Eq a) => Eq [a] where
244 {-# SPECIALISE instance Eq [Char] #-}
246 (x:xs) == (y:ys) = x == y && xs == ys
249 instance (Ord a) => Ord [a] where
250 {-# SPECIALISE instance Ord [Char] #-}
252 compare [] (_:_) = LT
253 compare (_:_) [] = GT
254 compare (x:xs) (y:ys) = case compare x y of
258 instance Functor [] where
261 instance Monad [] where
262 m >>= k = foldr ((++) . k) [] m
263 m >> k = foldr ((++) . (\ _ -> k)) [] m
268 A few list functions that appear here because they are used here.
269 The rest of the prelude list functions are in GHC.List.
271 ----------------------------------------------
272 -- foldr/build/augment
273 ----------------------------------------------
276 -- | 'foldr', applied to a binary operator, a starting value (typically
277 -- the right-identity of the operator), and a list, reduces the list
278 -- using the binary operator, from right to left:
280 -- > foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
282 foldr :: (a -> b -> b) -> b -> [a] -> b
284 -- foldr f z (x:xs) = f x (foldr f z xs)
285 {-# INLINE [0] foldr #-}
286 -- Inline only in the final stage, after the foldr/cons rule has had a chance
287 -- Also note that we inline it when it has *two* parameters, which are the
288 -- ones we are keen about specialising!
292 go (y:ys) = y `k` go ys
294 -- | A list producer that can be fused with 'foldr'.
295 -- This function is merely
297 -- > build g = g (:) []
299 -- but GHC's simplifier will transform an expression of the form
300 -- @'foldr' k z ('build' g)@, which may arise after inlining, to @g k z@,
301 -- which avoids producing an intermediate list.
303 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
304 {-# INLINE [1] build #-}
305 -- The INLINE is important, even though build is tiny,
306 -- because it prevents [] getting inlined in the version that
307 -- appears in the interface file. If [] *is* inlined, it
308 -- won't match with [] appearing in rules in an importing module.
310 -- The "1" says to inline in phase 1
314 -- | A list producer that can be fused with 'foldr'.
315 -- This function is merely
317 -- > augment g xs = g (:) xs
319 -- but GHC's simplifier will transform an expression of the form
320 -- @'foldr' k z ('augment' g xs)@, which may arise after inlining, to
321 -- @g k ('foldr' k z xs)@, which avoids producing an intermediate list.
323 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
324 {-# INLINE [1] augment #-}
325 augment g xs = g (:) xs
328 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
329 foldr k z (build g) = g k z
331 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
332 foldr k z (augment g xs) = g k (foldr k z xs)
334 "foldr/id" foldr (:) [] = \x -> x
335 "foldr/app" [1] forall ys. foldr (:) ys = \xs -> xs ++ ys
336 -- Only activate this from phase 1, because that's
337 -- when we disable the rule that expands (++) into foldr
339 -- The foldr/cons rule looks nice, but it can give disastrously
340 -- bloated code when commpiling
341 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
342 -- i.e. when there are very very long literal lists
343 -- So I've disabled it for now. We could have special cases
344 -- for short lists, I suppose.
345 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
347 "foldr/single" forall k z x. foldr k z [x] = k x z
348 "foldr/nil" forall k z. foldr k z [] = z
350 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
351 (h::forall b. (a->b->b) -> b -> b) .
352 augment g (build h) = build (\c n -> g c (h c n))
353 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
354 augment g [] = build g
357 -- This rule is true, but not (I think) useful:
358 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
362 ----------------------------------------------
364 ----------------------------------------------
367 -- | 'map' @f xs@ is the list obtained by applying @f@ to each element
370 -- > map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
371 -- > map f [x1, x2, ...] == [f x1, f x2, ...]
373 map :: (a -> b) -> [a] -> [b]
375 map f (x:xs) = f x : map f xs
378 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
379 {-# INLINE [0] mapFB #-}
380 mapFB c f x ys = c (f x) ys
382 -- The rules for map work like this.
384 -- Up to (but not including) phase 1, we use the "map" rule to
385 -- rewrite all saturated applications of map with its build/fold
386 -- form, hoping for fusion to happen.
387 -- In phase 1 and 0, we switch off that rule, inline build, and
388 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
389 -- thing back into plain map.
391 -- It's important that these two rules aren't both active at once
392 -- (along with build's unfolding) else we'd get an infinite loop
393 -- in the rules. Hence the activation control below.
395 -- The "mapFB" rule optimises compositions of map.
397 -- This same pattern is followed by many other functions:
398 -- e.g. append, filter, iterate, repeat, etc.
401 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
402 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
403 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
408 ----------------------------------------------
410 ----------------------------------------------
412 -- | Append two lists, i.e.,
414 -- > [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
415 -- > [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]
417 -- If the first list is not finite, the result is the first list.
419 (++) :: [a] -> [a] -> [a]
421 (++) (x:xs) ys = x : xs ++ ys
424 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
430 %*********************************************************
432 \subsection{Type @Bool@}
434 %*********************************************************
437 -- |'otherwise' is defined as the value 'True'. It helps to make
438 -- guards more readable. eg.
440 -- > f x | x < 0 = ...
441 -- > | otherwise = ...
446 %*********************************************************
448 \subsection{Type @Char@ and @String@}
450 %*********************************************************
453 -- | A 'String' is a list of characters. String constants in Haskell are values
458 {-| The character type 'Char' is an enumeration whose values represent
459 Unicode (or equivalently ISO\/IEC 10646) characters
460 (see <http://www.unicode.org/> for details).
461 This set extends the ISO 8859-1 (Latin-1) character set
462 (the first 256 charachers), which is itself an extension of the ASCII
463 character set (the first 128 characters).
464 A character literal in Haskell has type 'Char'.
466 To convert a 'Char' to or from the corresponding 'Int' value defined
467 by Unicode, use 'Prelude.toEnum' and 'Prelude.fromEnum' from the
468 'Prelude.Enum' class respectively (or equivalently 'ord' and 'chr').
472 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
473 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
474 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
475 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
476 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
477 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
480 -- | The 'Prelude.toEnum' method restricted to the type 'Data.Char.Char'.
483 | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
485 = error ("Prelude.chr: bad argument: " ++ showSignedInt (I# 9#) i "")
487 unsafeChr :: Int -> Char
488 unsafeChr (I# i#) = C# (chr# i#)
490 -- | The 'Prelude.fromEnum' method restricted to the type 'Data.Char.Char'.
492 ord (C# c#) = I# (ord# c#)
495 String equality is used when desugaring pattern-matches against strings.
498 eqString :: String -> String -> Bool
499 eqString [] [] = True
500 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
503 {-# RULES "eqString" (==) = eqString #-}
504 -- eqString also has a BuiltInRule in PrelRules.lhs:
505 -- eqString (unpackCString# (Lit s1)) (unpackCString# (Lit s2) = s1==s2
509 %*********************************************************
511 \subsection{Type @Int@}
513 %*********************************************************
516 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
521 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
522 #if WORD_SIZE_IN_BITS == 31
523 minInt = I# (-0x40000000#)
524 maxInt = I# 0x3FFFFFFF#
525 #elif WORD_SIZE_IN_BITS == 32
526 minInt = I# (-0x80000000#)
527 maxInt = I# 0x7FFFFFFF#
529 minInt = I# (-0x8000000000000000#)
530 maxInt = I# 0x7FFFFFFFFFFFFFFF#
533 instance Eq Int where
537 instance Ord Int where
544 compareInt :: Int -> Int -> Ordering
545 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
547 compareInt# :: Int# -> Int# -> Ordering
555 %*********************************************************
557 \subsection{The function type}
559 %*********************************************************
562 -- | Identity function.
566 -- | The call '(lazy e)' means the same as 'e', but 'lazy' has a
567 -- magical strictness property: it is lazy in its first argument,
568 -- even though its semantics is strict.
571 -- Implementation note: its strictness and unfolding are over-ridden
572 -- by the definition in MkId.lhs; in both cases to nothing at all.
573 -- That way, 'lazy' does not get inlined, and the strictness analyser
574 -- sees it as lazy. Then the worker/wrapper phase inlines it.
577 -- Assertion function. This simply ignores its boolean argument.
578 -- The compiler may rewrite it to @('assertError' line)@.
580 -- | If the first argument evaluates to 'True', then the result is the
581 -- second argument. Otherwise an 'AssertionFailed' exception is raised,
582 -- containing a 'String' with the source file and line number of the
585 -- Assertions can normally be turned on or off with a compiler flag
586 -- (for GHC, assertions are normally on unless optimisation is turned on
587 -- with @-O@ or the @-fignore-asserts@
588 -- option is given). When assertions are turned off, the first
589 -- argument to 'assert' is ignored, and the second argument is
590 -- returned as the result.
592 -- SLPJ: in 5.04 etc 'assert' is in GHC.Prim,
593 -- but from Template Haskell onwards it's simply
594 -- defined here in Base.lhs
595 assert :: Bool -> a -> a
601 breakpointCond :: Bool -> a -> a
602 breakpointCond _ r = r
604 data Opaque = forall a. O a
606 -- | Constant function.
610 -- | Function composition.
612 -- Make sure it has TWO args only on the left, so that it inlines
613 -- when applied to two functions, even if there is no final argument
614 (.) :: (b -> c) -> (a -> b) -> a -> c
615 (.) f g = \x -> f (g x)
617 -- | @'flip' f@ takes its (first) two arguments in the reverse order of @f@.
618 flip :: (a -> b -> c) -> b -> a -> c
621 -- | Application operator. This operator is redundant, since ordinary
622 -- application @(f x)@ means the same as @(f '$' x)@. However, '$' has
623 -- low, right-associative binding precedence, so it sometimes allows
624 -- parentheses to be omitted; for example:
626 -- > f $ g $ h x = f (g (h x))
628 -- It is also useful in higher-order situations, such as @'map' ('$' 0) xs@,
629 -- or @'Data.List.zipWith' ('$') fs xs@.
631 ($) :: (a -> b) -> a -> b
634 -- | @'until' p f@ yields the result of applying @f@ until @p@ holds.
635 until :: (a -> Bool) -> (a -> a) -> a -> a
636 until p f x | p x = x
637 | otherwise = until p f (f x)
639 -- | 'asTypeOf' is a type-restricted version of 'const'. It is usually
640 -- used as an infix operator, and its typing forces its first argument
641 -- (which is usually overloaded) to have the same type as the second.
642 asTypeOf :: a -> a -> a
646 %*********************************************************
648 \subsection{@Functor@ and @Monad@ instances for @IO@}
650 %*********************************************************
653 instance Functor IO where
654 fmap f x = x >>= (return . f)
656 instance Monad IO where
657 {-# INLINE return #-}
660 m >> k = m >>= \ _ -> k
663 fail s = GHC.IO.failIO s
665 returnIO :: a -> IO a
666 returnIO x = IO $ \ s -> (# s, x #)
668 bindIO :: IO a -> (a -> IO b) -> IO b
669 bindIO (IO m) k = IO $ \ s -> case m s of (# new_s, a #) -> unIO (k a) new_s
671 thenIO :: IO a -> IO b -> IO b
672 thenIO (IO m) k = IO $ \ s -> case m s of (# new_s, _ #) -> unIO k new_s
674 unIO :: IO a -> (State# RealWorld -> (# State# RealWorld, a #))
678 %*********************************************************
680 \subsection{@getTag@}
682 %*********************************************************
684 Returns the 'tag' of a constructor application; this function is used
685 by the deriving code for Eq, Ord and Enum.
687 The primitive dataToTag# requires an evaluated constructor application
688 as its argument, so we provide getTag as a wrapper that performs the
689 evaluation before calling dataToTag#. We could have dataToTag#
690 evaluate its argument, but we prefer to do it this way because (a)
691 dataToTag# can be an inline primop if it doesn't need to do any
692 evaluation, and (b) we want to expose the evaluation to the
693 simplifier, because it might be possible to eliminate the evaluation
694 in the case when the argument is already known to be evaluated.
697 {-# INLINE getTag #-}
699 getTag x = x `seq` dataToTag# x
702 %*********************************************************
704 \subsection{Numeric primops}
706 %*********************************************************
709 divInt# :: Int# -> Int# -> Int#
711 -- Be careful NOT to overflow if we do any additional arithmetic
712 -- on the arguments... the following previous version of this
713 -- code has problems with overflow:
714 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
715 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
716 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
717 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
718 | otherwise = x# `quotInt#` y#
720 modInt# :: Int# -> Int# -> Int#
722 | (x# ># 0#) && (y# <# 0#) ||
723 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
726 !r# = x# `remInt#` y#
729 Definitions of the boxed PrimOps; these will be
730 used in the case of partial applications, etc.
739 {-# INLINE plusInt #-}
740 {-# INLINE minusInt #-}
741 {-# INLINE timesInt #-}
742 {-# INLINE quotInt #-}
743 {-# INLINE remInt #-}
744 {-# INLINE negateInt #-}
746 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt :: Int -> Int -> Int
747 (I# x) `plusInt` (I# y) = I# (x +# y)
748 (I# x) `minusInt` (I# y) = I# (x -# y)
749 (I# x) `timesInt` (I# y) = I# (x *# y)
750 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
751 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
752 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
753 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
756 "x# +# 0#" forall x#. x# +# 0# = x#
757 "0# +# x#" forall x#. 0# +# x# = x#
758 "x# -# 0#" forall x#. x# -# 0# = x#
759 "x# -# x#" forall x#. x# -# x# = 0#
760 "x# *# 0#" forall x#. x# *# 0# = 0#
761 "0# *# x#" forall x#. 0# *# x# = 0#
762 "x# *# 1#" forall x#. x# *# 1# = x#
763 "1# *# x#" forall x#. 1# *# x# = x#
766 negateInt :: Int -> Int
767 negateInt (I# x) = I# (negateInt# x)
769 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
770 (I# x) `gtInt` (I# y) = x ># y
771 (I# x) `geInt` (I# y) = x >=# y
772 (I# x) `eqInt` (I# y) = x ==# y
773 (I# x) `neInt` (I# y) = x /=# y
774 (I# x) `ltInt` (I# y) = x <# y
775 (I# x) `leInt` (I# y) = x <=# y
778 "x# ># x#" forall x#. x# ># x# = False
779 "x# >=# x#" forall x#. x# >=# x# = True
780 "x# ==# x#" forall x#. x# ==# x# = True
781 "x# /=# x#" forall x#. x# /=# x# = False
782 "x# <# x#" forall x#. x# <# x# = False
783 "x# <=# x#" forall x#. x# <=# x# = True
787 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
788 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
789 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
790 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
791 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
792 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
793 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
794 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
795 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
799 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
800 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
801 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
802 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
803 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
804 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
808 We'd like to have more rules, but for example:
810 This gives wrong answer (0) for NaN - NaN (should be NaN):
811 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
813 This gives wrong answer (0) for 0 * NaN (should be NaN):
814 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
816 This gives wrong answer (0) for NaN * 0 (should be NaN):
817 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
819 These are tested by num014.
822 -- Wrappers for the shift operations. The uncheckedShift# family are
823 -- undefined when the amount being shifted by is greater than the size
824 -- in bits of Int#, so these wrappers perform a check and return
825 -- either zero or -1 appropriately.
827 -- Note that these wrappers still produce undefined results when the
828 -- second argument (the shift amount) is negative.
830 -- | Shift the argument left by the specified number of bits
831 -- (which must be non-negative).
832 shiftL# :: Word# -> Int# -> Word#
833 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
834 | otherwise = a `uncheckedShiftL#` b
836 -- | Shift the argument right by the specified number of bits
837 -- (which must be non-negative).
838 shiftRL# :: Word# -> Int# -> Word#
839 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
840 | otherwise = a `uncheckedShiftRL#` b
842 -- | Shift the argument left by the specified number of bits
843 -- (which must be non-negative).
844 iShiftL# :: Int# -> Int# -> Int#
845 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
846 | otherwise = a `uncheckedIShiftL#` b
848 -- | Shift the argument right (signed) by the specified number of bits
849 -- (which must be non-negative).
850 iShiftRA# :: Int# -> Int# -> Int#
851 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
852 | otherwise = a `uncheckedIShiftRA#` b
854 -- | Shift the argument right (unsigned) by the specified number of bits
855 -- (which must be non-negative).
856 iShiftRL# :: Int# -> Int# -> Int#
857 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
858 | otherwise = a `uncheckedIShiftRL#` b
860 #if WORD_SIZE_IN_BITS == 32
862 "narrow32Int#" forall x#. narrow32Int# x# = x#
863 "narrow32Word#" forall x#. narrow32Word# x# = x#
868 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
869 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
874 %********************************************************
876 \subsection{Unpacking C strings}
878 %********************************************************
880 This code is needed for virtually all programs, since it's used for
881 unpacking the strings of error messages.
884 unpackCString# :: Addr# -> [Char]
885 {-# NOINLINE unpackCString# #-}
886 -- There's really no point in inlining this, ever, cos
887 -- the loop doesn't specialise in an interesting
888 -- But it's pretty small, so there's a danger that
889 -- it'll be inlined at every literal, which is a waste
894 | ch `eqChar#` '\0'# = []
895 | otherwise = C# ch : unpack (nh +# 1#)
897 !ch = indexCharOffAddr# addr nh
899 unpackAppendCString# :: Addr# -> [Char] -> [Char]
900 {-# NOINLINE unpackAppendCString# #-}
901 -- See the NOINLINE note on unpackCString#
902 unpackAppendCString# addr rest
906 | ch `eqChar#` '\0'# = rest
907 | otherwise = C# ch : unpack (nh +# 1#)
909 !ch = indexCharOffAddr# addr nh
911 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
913 -- Usually the unpack-list rule turns unpackFoldrCString# into unpackCString#
915 -- It also has a BuiltInRule in PrelRules.lhs:
916 -- unpackFoldrCString# "foo" c (unpackFoldrCString# "baz" c n)
917 -- = unpackFoldrCString# "foobaz" c n
919 {-# NOINLINE unpackFoldrCString# #-}
920 -- At one stage I had NOINLINE [0] on the grounds that, unlike
921 -- unpackCString#, there *is* some point in inlining
922 -- unpackFoldrCString#, because we get better code for the
923 -- higher-order function call. BUT there may be a lot of
924 -- literal strings, and making a separate 'unpack' loop for
925 -- each is highly gratuitous. See nofib/real/anna/PrettyPrint.
927 unpackFoldrCString# addr f z
931 | ch `eqChar#` '\0'# = z
932 | otherwise = C# ch `f` unpack (nh +# 1#)
934 !ch = indexCharOffAddr# addr nh
936 unpackCStringUtf8# :: Addr# -> [Char]
937 unpackCStringUtf8# addr
941 | ch `eqChar#` '\0'# = []
942 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
943 | ch `leChar#` '\xDF'# =
944 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
945 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
947 | ch `leChar#` '\xEF'# =
948 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
949 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
950 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
953 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
954 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
955 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
956 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
959 !ch = indexCharOffAddr# addr nh
961 unpackNBytes# :: Addr# -> Int# -> [Char]
962 unpackNBytes# _addr 0# = []
963 unpackNBytes# addr len# = unpack [] (len# -# 1#)
968 case indexCharOffAddr# addr i# of
969 ch -> unpack (C# ch : acc) (i# -# 1#)
972 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
973 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
974 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
976 -- There's a built-in rule (in PrelRules.lhs) for
977 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n
984 -- | A special argument for the 'Control.Monad.ST.ST' type constructor,
985 -- indexing a state embedded in the 'Prelude.IO' monad by
986 -- 'Control.Monad.ST.stToIO'.