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 (==), (/=) :: a -> a -> Bool
155 x /= y = not (x == y)
156 x == y = not (x /= y)
158 class (Eq a) => Ord a where
159 compare :: a -> a -> Ordering
160 (<), (<=), (>), (>=) :: a -> a -> Bool
161 max, min :: a -> a -> a
163 -- An instance of Ord should define either 'compare' or '<='.
164 -- Using 'compare' can be more efficient for complex types.
168 | x <= y = LT -- NB: must be '<=' not '<' to validate the
169 -- above claim about the minimal things that
170 -- can be defined for an instance of Ord
173 x < y = case compare x y of { LT -> True; _other -> False }
174 x <= y = case compare x y of { GT -> False; _other -> True }
175 x > y = case compare x y of { GT -> True; _other -> False }
176 x >= y = case compare x y of { LT -> False; _other -> True }
178 -- These two default methods use '<=' rather than 'compare'
179 -- because the latter is often more expensive
180 max x y = if x <= y then y else x
181 min x y = if x <= y then x else y
184 %*********************************************************
186 \subsection{Monadic classes @Functor@, @Monad@ }
188 %*********************************************************
191 class Functor f where
192 fmap :: (a -> b) -> f a -> f b
195 (>>=) :: m a -> (a -> m b) -> m b
196 (>>) :: m a -> m b -> m b
198 fail :: String -> m a
200 m >> k = m >>= \_ -> k
205 %*********************************************************
207 \subsection{The list type}
209 %*********************************************************
212 data [] a = [] | a : [a] -- do explicitly: deriving (Eq, Ord)
213 -- to avoid weird names like con2tag_[]#
216 instance (Eq a) => Eq [a] where
217 {-# SPECIALISE instance Eq [Char] #-}
219 (x:xs) == (y:ys) = x == y && xs == ys
222 instance (Ord a) => Ord [a] where
223 {-# SPECIALISE instance Ord [Char] #-}
225 compare [] (_:_) = LT
226 compare (_:_) [] = GT
227 compare (x:xs) (y:ys) = case compare x y of
231 instance Functor [] where
234 instance Monad [] where
235 m >>= k = foldr ((++) . k) [] m
236 m >> k = foldr ((++) . (\ _ -> k)) [] m
241 A few list functions that appear here because they are used here.
242 The rest of the prelude list functions are in GHC.List.
244 ----------------------------------------------
245 -- foldr/build/augment
246 ----------------------------------------------
249 foldr :: (a -> b -> b) -> b -> [a] -> b
251 -- foldr f z (x:xs) = f x (foldr f z xs)
252 {-# INLINE [0] foldr #-}
253 -- Inline only in the final stage, after the foldr/cons rule has had a chance
257 go (y:ys) = y `k` go ys
259 build :: forall a. (forall b. (a -> b -> b) -> b -> b) -> [a]
260 {-# INLINE [1] build #-}
261 -- The INLINE is important, even though build is tiny,
262 -- because it prevents [] getting inlined in the version that
263 -- appears in the interface file. If [] *is* inlined, it
264 -- won't match with [] appearing in rules in an importing module.
266 -- The "1" says to inline in phase 1
270 augment :: forall a. (forall b. (a->b->b) -> b -> b) -> [a] -> [a]
271 {-# INLINE [1] augment #-}
272 augment g xs = g (:) xs
275 "fold/build" forall k z (g::forall b. (a->b->b) -> b -> b) .
276 foldr k z (build g) = g k z
278 "foldr/augment" forall k z xs (g::forall b. (a->b->b) -> b -> b) .
279 foldr k z (augment g xs) = g k (foldr k z xs)
281 "foldr/id" foldr (:) [] = \x->x
282 "foldr/app" [1] forall xs ys. foldr (:) ys xs = xs ++ ys
283 -- Only activate this from phase 1, because that's
284 -- when we disable the rule that expands (++) into foldr
286 -- The foldr/cons rule looks nice, but it can give disastrously
287 -- bloated code when commpiling
288 -- array (a,b) [(1,2), (2,2), (3,2), ...very long list... ]
289 -- i.e. when there are very very long literal lists
290 -- So I've disabled it for now. We could have special cases
291 -- for short lists, I suppose.
292 -- "foldr/cons" forall k z x xs. foldr k z (x:xs) = k x (foldr k z xs)
294 "foldr/single" forall k z x. foldr k z [x] = k x z
295 "foldr/nil" forall k z. foldr k z [] = z
297 "augment/build" forall (g::forall b. (a->b->b) -> b -> b)
298 (h::forall b. (a->b->b) -> b -> b) .
299 augment g (build h) = build (\c n -> g c (h c n))
300 "augment/nil" forall (g::forall b. (a->b->b) -> b -> b) .
301 augment g [] = build g
304 -- This rule is true, but not (I think) useful:
305 -- augment g (augment h t) = augment (\cn -> g c (h c n)) t
309 ----------------------------------------------
311 ----------------------------------------------
314 map :: (a -> b) -> [a] -> [b]
316 map f (x:xs) = f x : map f xs
319 mapFB :: (elt -> lst -> lst) -> (a -> elt) -> a -> lst -> lst
320 {-# INLINE [0] mapFB #-}
321 mapFB c f x ys = c (f x) ys
323 -- The rules for map work like this.
325 -- Up to (but not including) phase 1, we use the "map" rule to
326 -- rewrite all saturated applications of map with its build/fold
327 -- form, hoping for fusion to happen.
328 -- In phase 1 and 0, we switch off that rule, inline build, and
329 -- switch on the "mapList" rule, which rewrites the foldr/mapFB
330 -- thing back into plain map.
332 -- It's important that these two rules aren't both active at once
333 -- (along with build's unfolding) else we'd get an infinite loop
334 -- in the rules. Hence the activation control below.
336 -- The "mapFB" rule optimises compositions of map.
338 -- This same pattern is followed by many other functions:
339 -- e.g. append, filter, iterate, repeat, etc.
342 "map" [~1] forall f xs. map f xs = build (\c n -> foldr (mapFB c f) n xs)
343 "mapList" [1] forall f. foldr (mapFB (:) f) [] = map f
344 "mapFB" forall c f g. mapFB (mapFB c f) g = mapFB c (f.g)
349 ----------------------------------------------
351 ----------------------------------------------
353 (++) :: [a] -> [a] -> [a]
355 (++) (x:xs) ys = x : xs ++ ys
358 "++" [~1] forall xs ys. xs ++ ys = augment (\c n -> foldr c n xs) ys
364 %*********************************************************
366 \subsection{Type @Bool@}
368 %*********************************************************
371 data Bool = False | True deriving (Eq, Ord)
372 -- Read in GHC.Read, Show in GHC.Show
376 (&&), (||) :: Bool -> Bool -> Bool
391 %*********************************************************
393 \subsection{The @()@ type}
395 %*********************************************************
397 The Unit type is here because virtually any program needs it (whereas
398 some programs may get away without consulting GHC.Tup). Furthermore,
399 the renamer currently *always* asks for () to be in scope, so that
400 ccalls can use () as their default type; so when compiling GHC.Base we
401 need (). (We could arrange suck in () only if -fglasgow-exts, but putting
402 it here seems more direct.)
411 instance Ord () where
422 %*********************************************************
424 \subsection{Type @Ordering@}
426 %*********************************************************
429 data Ordering = LT | EQ | GT deriving (Eq, Ord)
430 -- Read in GHC.Read, Show in GHC.Show
434 %*********************************************************
436 \subsection{Type @Char@ and @String@}
438 %*********************************************************
445 -- We don't use deriving for Eq and Ord, because for Ord the derived
446 -- instance defines only compare, which takes two primops. Then
447 -- '>' uses compare, and therefore takes two primops instead of one.
449 instance Eq Char where
450 (C# c1) == (C# c2) = c1 `eqChar#` c2
451 (C# c1) /= (C# c2) = c1 `neChar#` c2
453 instance Ord Char where
454 (C# c1) > (C# c2) = c1 `gtChar#` c2
455 (C# c1) >= (C# c2) = c1 `geChar#` c2
456 (C# c1) <= (C# c2) = c1 `leChar#` c2
457 (C# c1) < (C# c2) = c1 `ltChar#` c2
460 "x# `eqChar#` x#" forall x#. x# `eqChar#` x# = True
461 "x# `neChar#` x#" forall x#. x# `neChar#` x# = False
462 "x# `gtChar#` x#" forall x#. x# `gtChar#` x# = False
463 "x# `geChar#` x#" forall x#. x# `geChar#` x# = True
464 "x# `leChar#` x#" forall x#. x# `leChar#` x# = True
465 "x# `ltChar#` x#" forall x#. x# `ltChar#` x# = False
469 chr (I# i#) | int2Word# i# `leWord#` int2Word# 0x10FFFF# = C# (chr# i#)
470 | otherwise = error "Prelude.chr: bad argument"
472 unsafeChr :: Int -> Char
473 unsafeChr (I# i#) = C# (chr# i#)
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
485 eqString cs1 cs2 = False
487 {-# RULES "eqString" (==) = eqString #-}
491 %*********************************************************
493 \subsection{Type @Int@}
495 %*********************************************************
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 %*********************************************************
554 -- function composition
556 (.) :: (b -> c) -> (a -> b) -> a -> c
559 -- flip f takes its (first) two arguments in the reverse order of f.
560 flip :: (a -> b -> c) -> b -> a -> c
563 -- right-associating infix application operator (useful in continuation-
566 ($) :: (a -> b) -> a -> b
569 -- until p f yields the result of applying f until p holds.
570 until :: (a -> Bool) -> (a -> a) -> a -> a
571 until p f x | p x = x
572 | otherwise = until p f (f x)
574 -- asTypeOf is a type-restricted version of const. It is usually used
575 -- as an infix operator, and its typing forces its first argument
576 -- (which is usually overloaded) to have the same type as the second.
577 asTypeOf :: a -> a -> a
581 %*********************************************************
583 \subsection{CCallable instances}
585 %*********************************************************
587 Defined here to avoid orphans
590 instance CCallable Char
591 instance CReturnable Char
593 instance CCallable Int
594 instance CReturnable Int
596 instance CReturnable () -- Why, exactly?
600 %*********************************************************
602 \subsection{Generics}
604 %*********************************************************
609 data (:+:) a b = Inl a | Inr b
610 data (:*:) a b = a :*: b
615 %*********************************************************
617 \subsection{Numeric primops}
619 %*********************************************************
622 divInt#, modInt# :: Int# -> Int# -> Int#
624 | (x# ># 0#) && (y# <# 0#) = ((x# -# y#) -# 1#) `quotInt#` y#
625 | (x# <# 0#) && (y# ># 0#) = ((x# -# y#) +# 1#) `quotInt#` y#
626 | otherwise = x# `quotInt#` y#
628 | (x# ># 0#) && (y# <# 0#) ||
629 (x# <# 0#) && (y# ># 0#) = if r# /=# 0# then r# +# y# else 0#
635 Definitions of the boxed PrimOps; these will be
636 used in the case of partial applications, etc.
645 {-# INLINE plusInt #-}
646 {-# INLINE minusInt #-}
647 {-# INLINE timesInt #-}
648 {-# INLINE quotInt #-}
649 {-# INLINE remInt #-}
650 {-# INLINE negateInt #-}
652 plusInt, minusInt, timesInt, quotInt, remInt, divInt, modInt, gcdInt :: Int -> Int -> Int
653 (I# x) `plusInt` (I# y) = I# (x +# y)
654 (I# x) `minusInt` (I# y) = I# (x -# y)
655 (I# x) `timesInt` (I# y) = I# (x *# y)
656 (I# x) `quotInt` (I# y) = I# (x `quotInt#` y)
657 (I# x) `remInt` (I# y) = I# (x `remInt#` y)
658 (I# x) `divInt` (I# y) = I# (x `divInt#` y)
659 (I# x) `modInt` (I# y) = I# (x `modInt#` y)
662 "x# +# 0#" forall x#. x# +# 0# = x#
663 "0# +# x#" forall x#. 0# +# x# = x#
664 "x# -# 0#" forall x#. x# -# 0# = x#
665 "x# -# x#" forall x#. x# -# x# = 0#
666 "x# *# 0#" forall x#. x# *# 0# = 0#
667 "0# *# x#" forall x#. 0# *# x# = 0#
668 "x# *# 1#" forall x#. x# *# 1# = x#
669 "1# *# x#" forall x#. 1# *# x# = x#
672 gcdInt (I# a) (I# b) = g a b
673 where g 0# 0# = error "GHC.Base.gcdInt: gcd 0 0 is undefined"
676 g _ _ = I# (gcdInt# absA absB)
678 absInt x = if x <# 0# then negateInt# x else x
683 negateInt :: Int -> Int
684 negateInt (I# x) = I# (negateInt# x)
686 gtInt, geInt, eqInt, neInt, ltInt, leInt :: Int -> Int -> Bool
687 (I# x) `gtInt` (I# y) = x ># y
688 (I# x) `geInt` (I# y) = x >=# y
689 (I# x) `eqInt` (I# y) = x ==# y
690 (I# x) `neInt` (I# y) = x /=# y
691 (I# x) `ltInt` (I# y) = x <# y
692 (I# x) `leInt` (I# y) = x <=# y
695 "x# ># x#" forall x#. x# ># x# = False
696 "x# >=# x#" forall x#. x# >=# x# = True
697 "x# ==# x#" forall x#. x# ==# x# = True
698 "x# /=# x#" forall x#. x# /=# x# = False
699 "x# <# x#" forall x#. x# <# x# = False
700 "x# <=# x#" forall x#. x# <=# x# = True
704 "plusFloat x 0.0" forall x#. plusFloat# x# 0.0# = x#
705 "plusFloat 0.0 x" forall x#. plusFloat# 0.0# x# = x#
706 "minusFloat x 0.0" forall x#. minusFloat# x# 0.0# = x#
707 "minusFloat x x" forall x#. minusFloat# x# x# = 0.0#
708 "timesFloat x 0.0" forall x#. timesFloat# x# 0.0# = 0.0#
709 "timesFloat0.0 x" forall x#. timesFloat# 0.0# x# = 0.0#
710 "timesFloat x 1.0" forall x#. timesFloat# x# 1.0# = x#
711 "timesFloat 1.0 x" forall x#. timesFloat# 1.0# x# = x#
712 "divideFloat x 1.0" forall x#. divideFloat# x# 1.0# = x#
716 "plusDouble x 0.0" forall x#. (+##) x# 0.0## = x#
717 "plusDouble 0.0 x" forall x#. (+##) 0.0## x# = x#
718 "minusDouble x 0.0" forall x#. (-##) x# 0.0## = x#
719 "minusDouble x x" forall x#. (-##) x# x# = 0.0##
720 "timesDouble x 0.0" forall x#. (*##) x# 0.0## = 0.0##
721 "timesDouble 0.0 x" forall x#. (*##) 0.0## x# = 0.0##
722 "timesDouble x 1.0" forall x#. (*##) x# 1.0## = x#
723 "timesDouble 1.0 x" forall x#. (*##) 1.0## x# = x#
724 "divideDouble x 1.0" forall x#. (/##) x# 1.0## = x#
727 -- Wrappers for the shift operations. The uncheckedShift# family are
728 -- undefined when the amount being shifted by is greater than the size
729 -- in bits of Int#, so these wrappers perform a check and return
730 -- either zero or -1 appropriately.
732 -- Note that these wrappers still produce undefined results when the
733 -- second argument (the shift amount) is negative.
735 shiftL#, shiftRL# :: Word# -> Int# -> Word#
737 a `shiftL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
738 | otherwise = a `uncheckedShiftL#` b
740 a `shiftRL#` b | b >=# WORD_SIZE_IN_BITS# = int2Word# 0#
741 | otherwise = a `uncheckedShiftRL#` b
743 iShiftL#, iShiftRA#, iShiftRL# :: Int# -> Int# -> Int#
745 a `iShiftL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
746 | otherwise = a `uncheckedIShiftL#` b
748 a `iShiftRA#` b | b >=# WORD_SIZE_IN_BITS# = if a <# 0# then (-1#) else 0#
749 | otherwise = a `uncheckedIShiftRA#` b
751 a `iShiftRL#` b | b >=# WORD_SIZE_IN_BITS# = 0#
752 | otherwise = a `uncheckedIShiftRL#` b
754 #if WORD_SIZE_IN_BITS == 32
756 "narrow32Int#" forall x#. narrow32Int# x# = x#
757 "narrow32Word#" forall x#. narrow32Word# x# = x#
762 "int2Word2Int" forall x#. int2Word# (word2Int# x#) = x#
763 "word2Int2Word" forall x#. word2Int# (int2Word# x#) = x#
768 %********************************************************
770 \subsection{Unpacking C strings}
772 %********************************************************
774 This code is needed for virtually all programs, since it's used for
775 unpacking the strings of error messages.
778 unpackCString# :: Addr# -> [Char]
779 {-# NOINLINE [1] unpackCString# #-}
780 unpackCString# a = unpackCStringList# a
782 unpackCStringList# :: Addr# -> [Char]
783 unpackCStringList# addr
787 | ch `eqChar#` '\0'# = []
788 | otherwise = C# ch : unpack (nh +# 1#)
790 ch = indexCharOffAddr# addr nh
792 unpackAppendCString# :: Addr# -> [Char] -> [Char]
793 unpackAppendCString# addr rest
797 | ch `eqChar#` '\0'# = rest
798 | otherwise = C# ch : unpack (nh +# 1#)
800 ch = indexCharOffAddr# addr nh
802 unpackFoldrCString# :: Addr# -> (Char -> a -> a) -> a -> a
803 {-# NOINLINE [0] unpackFoldrCString# #-}
804 -- Don't inline till right at the end;
805 -- usually the unpack-list rule turns it into unpackCStringList
806 unpackFoldrCString# addr f z
810 | ch `eqChar#` '\0'# = z
811 | otherwise = C# ch `f` unpack (nh +# 1#)
813 ch = indexCharOffAddr# addr nh
815 unpackCStringUtf8# :: Addr# -> [Char]
816 unpackCStringUtf8# addr
820 | ch `eqChar#` '\0'# = []
821 | ch `leChar#` '\x7F'# = C# ch : unpack (nh +# 1#)
822 | ch `leChar#` '\xDF'# =
823 C# (chr# ((ord# ch -# 0xC0#) `uncheckedIShiftL#` 6# +#
824 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#))) :
826 | ch `leChar#` '\xEF'# =
827 C# (chr# ((ord# ch -# 0xE0#) `uncheckedIShiftL#` 12# +#
828 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 6# +#
829 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#))) :
832 C# (chr# ((ord# ch -# 0xF0#) `uncheckedIShiftL#` 18# +#
833 (ord# (indexCharOffAddr# addr (nh +# 1#)) -# 0x80#) `uncheckedIShiftL#` 12# +#
834 (ord# (indexCharOffAddr# addr (nh +# 2#)) -# 0x80#) `uncheckedIShiftL#` 6# +#
835 (ord# (indexCharOffAddr# addr (nh +# 3#)) -# 0x80#))) :
838 ch = indexCharOffAddr# addr nh
840 unpackNBytes# :: Addr# -> Int# -> [Char]
841 unpackNBytes# _addr 0# = []
842 unpackNBytes# addr len# = unpack [] (len# -# 1#)
847 case indexCharOffAddr# addr i# of
848 ch -> unpack (C# ch : acc) (i# -# 1#)
851 "unpack" [~1] forall a . unpackCString# a = build (unpackFoldrCString# a)
852 "unpack-list" [1] forall a . unpackFoldrCString# a (:) [] = unpackCStringList# a
853 "unpack-append" forall a n . unpackFoldrCString# a (:) n = unpackAppendCString# a n
855 -- There's a built-in rule (in GHC.Rules.lhs) for
856 -- unpackFoldr "foo" c (unpackFoldr "baz" c n) = unpackFoldr "foobaz" c n