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 Classes: CCallable, CReturnable
21 GHC.Base Classes: Eq, Ord, Functor, Monad
22 Types: list, (), Int, Bool, Ordering, Char, String
24 Data.Tup Types: tuples, plus instances for GHC.Base classes
26 GHC.Show Class: Show, plus instances for GHC.Base/GHC.Tup types
28 GHC.Enum Class: Enum, plus instances for GHC.Base/GHC.Tup types
30 Data.Maybe Type: Maybe, plus instances for GHC.Base classes
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 Ix Classes: Ix, plus instances for Int, Bool, Char, Integer, Ordering, tuples
48 GHC.Arr Types: Array, MutableArray, MutableVar
50 Does *not* contain any ByteArray stuff (see GHC.ByteArr)
51 Arrays are used by a function in GHC.Float
53 GHC.Float Classes: Floating, RealFloat
54 Types: Float, Double, plus instances of all classes so far
56 This module contains everything to do with floating point.
57 It is a big module (900 lines)
58 With a bit of luck, many modules can be compiled without ever reading GHC.Float.hi
60 GHC.ByteArr Types: ByteArray, MutableByteArray
62 We want this one to be after GHC.Float, because it defines arrays
66 Other Prelude modules are much easier with fewer complex dependencies.
69 {-# OPTIONS -fno-implicit-prelude #-}
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 -----------------------------------------------------------------------------
89 module GHC.Prim, -- Re-export GHC.Prim and GHC.Err, to avoid lots
90 module GHC.Err -- of people having to import it explicitly
95 import {-# SOURCE #-} GHC.Err
99 infix 4 ==, /=, <, <=, >=, >
105 default () -- Double isn't available yet
109 %*********************************************************
111 \subsection{DEBUGGING STUFF}
112 %* (for use when compiling GHC.Base itself doesn't work)
114 %*********************************************************
118 data Bool = False | True
119 data Ordering = LT | EQ | GT
127 (&&) True True = True
133 unpackCString# :: Addr# -> [Char]
134 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
135 unpackAppendCString# :: Addr# -> [Char] -> [Char]
136 unpackCStringUtf8# :: Addr# -> [Char]
137 unpackCString# a = error "urk"
138 unpackFoldrCString# a = error "urk"
139 unpackAppendCString# a = error "urk"
140 unpackCStringUtf8# a = error "urk"
145 %*********************************************************
147 \subsection{Standard classes @Eq@, @Ord@}
149 %*********************************************************
153 -- | The 'Eq' class defines equality ('==') and inequality ('/=').
154 -- All the basic datatypes exported by the "Prelude" are instances of 'Eq',
155 -- and 'Eq' may be derived for any datatype whose constituents are also
156 -- instances of 'Eq'.
158 -- Minimal complete definition: either '==' or '/='.
161 (==), (/=) :: a -> a -> Bool
163 x /= y = not (x == y)
164 x == y = not (x /= y)
166 class (Eq a) => Ord a where
167 compare :: a -> a -> Ordering
168 (<), (<=), (>), (>=) :: a -> a -> Bool
169 max, min :: a -> a -> a
171 -- An instance of Ord should define either 'compare' or '<='.
172 -- Using 'compare' can be more efficient for complex types.
176 | x <= y = LT -- NB: must be '<=' not '<' to validate the
177 -- above claim about the minimal things that
178 -- can be defined for an instance of Ord
181 x < y = case compare x y of { LT -> True; _other -> False }
182 x <= y = case compare x y of { GT -> False; _other -> True }
183 x > y = case compare x y of { GT -> True; _other -> False }
184 x >= y = case compare x y of { LT -> False; _other -> True }
186 -- These two default methods use '<=' rather than 'compare'
187 -- because the latter is often more expensive
188 max x y = if x <= y then y else x
189 min x y = if x <= y then x else y
192 %*********************************************************
194 \subsection{Monadic classes @Functor@, @Monad@ }
196 %*********************************************************
199 class Functor f where
200 fmap :: (a -> b) -> f a -> f b
203 (>>=) :: m a -> (a -> m b) -> m b
204 (>>) :: m a -> m b -> m b
206 fail :: String -> m a
208 m >> k = m >>= \_ -> k
213 %*********************************************************
215 \subsection{The list type}
217 %*********************************************************
220 data [] a = [] | a : [a] -- do explicitly: deriving (Eq, Ord)
221 -- to avoid weird names like con2tag_[]#
224 instance (Eq a) => Eq [a] where
225 {-# SPECIALISE instance Eq [Char] #-}
227 (x:xs) == (y:ys) = x == y && xs == ys
230 instance (Ord a) => Ord [a] where
231 {-# SPECIALISE instance Ord [Char] #-}
233 compare [] (_:_) = LT
234 compare (_:_) [] = GT
235 compare (x:xs) (y:ys) = case compare x y of
239 instance Functor [] where
242 instance Monad [] where
243 m >>= k = foldr ((++) . k) [] m
244 m >> k = foldr ((++) . (\ _ -> k)) [] m
249 A few list functions that appear here because they are used here.
250 The rest of the prelude list functions are in GHC.List.
252 ----------------------------------------------
253 -- foldr/build/augment
254 ----------------------------------------------
257 foldr :: (a -> b -> b) -> b -> [a] -> b
259 -- foldr f z (x:xs) = f x (foldr f z xs)
260 {-# INLINE [0] foldr #-}
261 -- Inline only in the final stage, after the foldr/cons rule has had a chance
265 go (y:ys) = y `k` go ys
267 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
268 {-# INLINE [1] build #-}
269 -- The INLINE is important, even though build is tiny,
270 -- because it prevents [] getting inlined in the version that
271 -- appears in the interface file. If [] *is* inlined, it
272 -- won't match with [] appearing in rules in an importing module.
274 -- The "1" says to inline in phase 1
278 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
279 {-# INLINE [1] augment #-}
280 augment g xs = g (:) xs
283 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
284 foldr k z (build g) = g k z
286 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
287 foldr k z (augment g xs) = g k (foldr k z xs)
289 "foldr/id" foldr (:) [] = \x->x
290 "foldr/app" [1] forall xs ys. foldr (:) ys xs = xs ++ ys
291 -- Only activate this from phase 1, because that's
292 -- when we disable the rule that expands (++) into foldr
294 -- The foldr/cons rule looks nice, but it can give disastrously
295 -- bloated code when commpiling
296 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
297 -- i.e. when there are very very long literal lists
298 -- So I've disabled it for now. We could have special cases
299 -- for short lists, I suppose.
300 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
302 "foldr/single" forall k z x. foldr k z [x] = k x z
303 "foldr/nil" forall k z. foldr k z [] = z
305 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
306 (h::forall b. (a->b->b) -> b -> b) .
307 augment g (build h) = build (\c n -> g c (h c n))
308 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
309 augment g [] = build g
312 -- This rule is true, but not (I think) useful:
313 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
317 ----------------------------------------------
319 ----------------------------------------------
322 map :: (a -> b) -> [a] -> [b]
324 map f (x:xs) = f x : map f xs
327 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
328 {-# INLINE [0] mapFB #-}
329 mapFB c f x ys = c (f x) ys
331 -- The rules for map work like this.
333 -- Up to (but not including) phase 1, we use the "map" rule to
334 -- rewrite all saturated applications of map with its build/fold
335 -- form, hoping for fusion to happen.
336 -- In phase 1 and 0, we switch off that rule, inline build, and
337 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
338 -- thing back into plain map.
340 -- It's important that these two rules aren't both active at once
341 -- (along with build's unfolding) else we'd get an infinite loop
342 -- in the rules. Hence the activation control below.
344 -- The "mapFB" rule optimises compositions of map.
346 -- This same pattern is followed by many other functions:
347 -- e.g. append, filter, iterate, repeat, etc.
350 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
351 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
352 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
357 ----------------------------------------------
359 ----------------------------------------------
361 (++) :: [a] -> [a] -> [a]
363 (++) (x:xs) ys = x : xs ++ ys
366 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
372 %*********************************************************
374 \subsection{Type @Bool@}
376 %*********************************************************
379 -- |The 'Bool' type is an enumeration. It is defined with 'False'
380 -- first so that the corresponding 'Enum' instance will give @'fromEnum'
381 -- False@ the value zero, and @'fromEnum' True@ the value 1.
382 data Bool = False | True deriving (Eq, Ord)
383 -- Read in GHC.Read, Show in GHC.Show
388 (&&) :: Bool -> Bool -> Bool
393 (||) :: Bool -> Bool -> Bool
402 -- |'otherwise' is defined as the value 'True'; it helps to make
403 -- guards more readable. eg.
405 -- > f x | x \< 0 = ...
406 -- > | otherwise = ...
412 %*********************************************************
414 \subsection{The @()@ type}
416 %*********************************************************
418 The Unit type is here because virtually any program needs it (whereas
419 some programs may get away without consulting GHC.Tup). Furthermore,
420 the renamer currently *always* asks for () to be in scope, so that
421 ccalls can use () as their default type; so when compiling GHC.Base we
422 need (). (We could arrange suck in () only if -fglasgow-exts, but putting
423 it here seems more direct.)
426 -- | The unit datatype @()@ has one non-undefined member, the nullary
434 instance Ord () where
445 %*********************************************************
447 \subsection{Type @Ordering@}
449 %*********************************************************
452 -- | Represents an ordering relationship between two values: less
453 -- than, equal to, or greater than. An 'Ordering' is returned by
455 data Ordering = LT | EQ | GT deriving (Eq, Ord)
456 -- Read in GHC.Read, Show in GHC.Show
460 %*********************************************************
462 \subsection{Type @Char@ and @String@}
464 %*********************************************************
467 -- | A 'String' is a list of characters. String constants in Haskell are values
472 {-| The character type 'Char' is an enumeration whose values represent
473 Unicode characters. A character literal in Haskell has type 'Char'.
475 To convert a 'Char' to or from an 'Int', use 'Prelude.toEnum' and
476 'Prelude.fromEnum' from the 'Enum' class respectively (equivalently
477 'ord' and 'chr' also do the trick).
481 -- We don't use deriving for Eq and Ord, because for Ord the derived
482 -- instance defines only compare, which takes two primops. Then
483 -- '>' uses compare, and therefore takes two primops instead of one.
485 instance Eq Char where
486 (C# c1) == (C# c2) = c1 `eqChar#` c2
487 (C# c1) /= (C# c2) = c1 `neChar#` c2
489 instance Ord Char where
490 (C# c1) > (C# c2) = c1 `gtChar#` c2
491 (C# c1) >= (C# c2) = c1 `geChar#` c2
492 (C# c1) <= (C# c2) = c1 `leChar#` c2
493 (C# c1) < (C# c2) = c1 `ltChar#` c2
496 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
497 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
498 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
499 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
500 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
501 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
505 chr (I# i#) | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
506 | otherwise = error "Prelude.chr: bad argument"
508 unsafeChr :: Int -> Char
509 unsafeChr (I# i#) = C# (chr# i#)
512 ord (C# c#) = I# (ord# c#)
515 String equality is used when desugaring pattern-matches against strings.
518 eqString :: String -> String -> Bool
519 eqString [] [] = True
520 eqString (c1:cs1) (c2:cs2) = c1 == c2 && cs1 `eqString` cs2
521 eqString cs1 cs2 = False
523 {-# RULES "eqString" (==) = eqString #-}
527 %*********************************************************
529 \subsection{Type @Int@}
531 %*********************************************************
535 -- ^A fixed-precision integer type with at least the range @[-2^29
536 -- .. 2^29-1]@. The exact range for a given implementation can be
537 -- determined by using 'minBound' and 'maxBound' from the 'Bounded'
540 zeroInt, oneInt, twoInt, maxInt, minInt :: Int
545 {- Seems clumsy. Should perhaps put minInt and MaxInt directly into MachDeps.h -}
546 #if WORD_SIZE_IN_BITS == 31
547 minInt = I# (-0x40000000#)
548 maxInt = I# 0x3FFFFFFF#
549 #elif WORD_SIZE_IN_BITS == 32
550 minInt = I# (-0x80000000#)
551 maxInt = I# 0x7FFFFFFF#
553 minInt = I# (-0x8000000000000000#)
554 maxInt = I# 0x7FFFFFFFFFFFFFFF#
557 instance Eq Int where
561 instance Ord Int where
568 compareInt :: Int -> Int -> Ordering
569 (I# x#) `compareInt` (I# y#) = compareInt# x# y#
571 compareInt# :: Int# -> Int# -> Ordering
579 %*********************************************************
581 \subsection{The function type}
583 %*********************************************************
590 -- lazy function; this is just the same as id, but its unfolding
591 -- and strictness are over-ridden by the definition in MkId.lhs
592 -- That way, it does not get inlined, and the strictness analyser
593 -- sees it as lazy. Then the worker/wrapper phase inlines it.
602 -- function composition
604 (.) :: (b -> c) -> (a -> b) -> a -> c
607 -- flip f takes its (first) two arguments in the reverse order of f.
608 flip :: (a -> b -> c) -> b -> a -> c
611 -- right-associating infix application operator (useful in continuation-
614 ($) :: (a -> b) -> a -> b
617 -- until p f yields the result of applying f until p holds.
618 until :: (a -> Bool) -> (a -> a) -> a -> a
619 until p f x | p x = x
620 | otherwise = until p f (f x)
622 -- asTypeOf is a type-restricted version of const. It is usually used
623 -- as an infix operator, and its typing forces its first argument
624 -- (which is usually overloaded) to have the same type as the second.
625 asTypeOf :: a -> a -> a
629 %*********************************************************
631 \subsection{CCallable instances}
633 %*********************************************************
635 Defined here to avoid orphans
638 instance CCallable Char
639 instance CReturnable Char
641 instance CCallable Int
642 instance CReturnable Int
644 instance CReturnable () -- Why, exactly?
648 %*********************************************************
650 \subsection{Generics}
652 %*********************************************************
657 data (:+:) a b = Inl a | Inr b
658 data (:*:) a b = a :*: b
663 %*********************************************************
665 \subsection{Numeric primops}
667 %*********************************************************
670 divInt# :: Int# -> Int# -> Int#
672 -- Be careful NOT to overflow if we do any additional arithmetic
673 -- on the arguments... the following previous version of this
674 -- code has problems with overflow:
675 -- | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
676 -- | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
677 | (x# ># 0#) && (y# <# 0#) = ((x# -# 1#) `quotInt#` y#) -# 1#
678 | (x# <# 0#) && (y# ># 0#) = ((x# +# 1#) `quotInt#` y#) -# 1#
679 | otherwise = x# `quotInt#` y#
681 modInt# :: Int# -> Int# -> Int#
683 | (x# ># 0#) && (y# <# 0#) ||
684 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
690 Definitions of the boxed PrimOps; these will be
691 used in the case of partial applications, etc.
700 {-# INLINE plusInt #-}
701 {-# INLINE minusInt #-}
702 {-# INLINE timesInt #-}
703 {-# INLINE quotInt #-}
704 {-# INLINE remInt #-}
705 {-# INLINE negateInt #-}
707 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
708 (I# x) `plusInt` (I# y) = I# (x +# y)
709 (I# x) `minusInt` (I# y) = I# (x -# y)
710 (I# x) `timesInt` (I# y) = I# (x *# y)
711 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
712 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
713 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
714 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
717 "x# +# 0#" forall x#. x# +# 0# = x#
718 "0# +# x#" forall x#. 0# +# x# = x#
719 "x# -# 0#" forall x#. x# -# 0# = x#
720 "x# -# x#" forall x#. x# -# x# = 0#
721 "x# *# 0#" forall x#. x# *# 0# = 0#
722 "0# *# x#" forall x#. 0# *# x# = 0#
723 "x# *# 1#" forall x#. x# *# 1# = x#
724 "1# *# x#" forall x#. 1# *# x# = x#
727 gcdInt (I# a) (I# b) = g a b
728 where g 0# 0# = error "GHC.Base.gcdInt: gcd 0 0 is undefined"
731 g _ _ = I# (gcdInt# absA absB)
733 absInt x = if x <# 0# then negateInt# x else x
738 negateInt :: Int -> Int
739 negateInt (I# x) = I# (negateInt# x)
741 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
742 (I# x) `gtInt` (I# y) = x ># y
743 (I# x) `geInt` (I# y) = x >=# y
744 (I# x) `eqInt` (I# y) = x ==# y
745 (I# x) `neInt` (I# y) = x /=# y
746 (I# x) `ltInt` (I# y) = x <# y
747 (I# x) `leInt` (I# y) = x <=# y
750 "x# ># x#" forall x#. x# ># x# = False
751 "x# >=# x#" forall x#. x# >=# x# = True
752 "x# ==# x#" forall x#. x# ==# x# = True
753 "x# /=# x#" forall x#. x# /=# x# = False
754 "x# <# x#" forall x#. x# <# x# = False
755 "x# <=# x#" forall x#. x# <=# x# = True
759 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
760 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
761 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
762 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
763 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
764 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
765 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
766 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
767 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
771 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
772 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
773 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
774 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
775 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
776 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
777 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
778 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
779 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
782 -- Wrappers for the shift operations. The uncheckedShift# family are
783 -- undefined when the amount being shifted by is greater than the size
784 -- in bits of Int#, so these wrappers perform a check and return
785 -- either zero or -1 appropriately.
787 -- Note that these wrappers still produce undefined results when the
788 -- second argument (the shift amount) is negative.
790 shiftL#, shiftRL# :: Word# -> Int# -> Word#
792 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
793 | otherwise = a `uncheckedShiftL#` b
795 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
796 | otherwise = a `uncheckedShiftRL#` b
798 iShiftL#, iShiftRA#, iShiftRL# :: Int# -> Int# -> Int#
800 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
801 | otherwise = a `uncheckedIShiftL#` b
803 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
804 | otherwise = a `uncheckedIShiftRA#` b
806 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
807 | otherwise = a `uncheckedIShiftRL#` b
809 #if WORD_SIZE_IN_BITS == 32
811 "narrow32Int#" forall x#. narrow32Int# x# = x#
812 "narrow32Word#" forall x#. narrow32Word# x# = x#
817 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
818 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
823 %********************************************************
825 \subsection{Unpacking C strings}
827 %********************************************************
829 This code is needed for virtually all programs, since it's used for
830 unpacking the strings of error messages.
833 unpackCString# :: Addr# -> [Char]
834 {-# NOINLINE [1] unpackCString# #-}
839 | ch `eqChar#` '\0'# = []
840 | otherwise = C# ch : unpack (nh +# 1#)
842 ch = indexCharOffAddr# addr nh
844 unpackAppendCString# :: Addr# -> [Char] -> [Char]
845 unpackAppendCString# addr rest
849 | ch `eqChar#` '\0'# = rest
850 | otherwise = C# ch : unpack (nh +# 1#)
852 ch = indexCharOffAddr# addr nh
854 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
855 {-# NOINLINE [0] unpackFoldrCString# #-}
856 -- Don't inline till right at the end;
857 -- usually the unpack-list rule turns it into unpackCStringList
858 unpackFoldrCString# addr f z
862 | ch `eqChar#` '\0'# = z
863 | otherwise = C# ch `f` unpack (nh +# 1#)
865 ch = indexCharOffAddr# addr nh
867 unpackCStringUtf8# :: Addr# -> [Char]
868 unpackCStringUtf8# addr
872 | ch `eqChar#` '\0'# = []
873 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
874 | ch `leChar#` '\xDF'# =
875 C# (chr# (((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6#) +#
876 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
878 | ch `leChar#` '\xEF'# =
879 C# (chr# (((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12#) +#
880 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
881 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
884 C# (chr# (((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18#) +#
885 ((ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12#) +#
886 ((ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6#) +#
887 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
890 ch = indexCharOffAddr# addr nh
892 unpackNBytes# :: Addr# -> Int# -> [Char]
893 unpackNBytes# _addr 0# = []
894 unpackNBytes# addr len# = unpack [] (len# -# 1#)
899 case indexCharOffAddr# addr i# of
900 ch -> unpack (C# ch : acc) (i# -# 1#)
903 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
904 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCString# a
905 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
907 -- There's a built-in rule (in PrelRules.lhs) for
908 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n