module GHC.List ( map, (++), filter, concat, head, last, tail, init, null, length, (!!), foldl, scanl, scanl1, foldr, foldr1, scanr, scanr1, iterate, repeat, replicate, cycle, take, drop, splitAt, takeWhile, dropWhile, span, break, reverse, and, or, any, all, elem, notElem, lookup, concatMap, zip, zip3, zipWith, zipWith3, unzip, unzip3, errorEmptyList, #ifndef USE_REPORT_PRELUDE takeUInt_append #endif ) where import Data.Maybe import GHC.Base infixl 9 !! infix 4 `elem`, `notElem`\end{code} %********************************************************* %* * \subsection{List-manipulation functions} %* * %********************************************************* \begin{code}
head :: [a] -> a
head (x:_) = x
head [] = badHead
badHead :: a
badHead = errorEmptyList "head"
tail :: [a] -> [a]
tail (_:xs) = xs
tail [] = errorEmptyList "tail"
last :: [a] -> a
#ifdef USE_REPORT_PRELUDE
last [x] = x
last (_:xs) = last xs
last [] = errorEmptyList "last"
#else
last [] = errorEmptyList "last"
last (x:xs) = last' x xs
where last' y [] = y
last' _ (y:ys) = last' y ys
#endif
init :: [a] -> [a]
#ifdef USE_REPORT_PRELUDE
init [x] = []
init (x:xs) = x : init xs
init [] = errorEmptyList "init"
#else
init [] = errorEmptyList "init"
init (x:xs) = init' x xs
where init' _ [] = []
init' y (z:zs) = y : init' z zs
#endif
null :: [a] -> Bool
null [] = True
null (_:_) = False
length :: [a] -> Int
length l = len l 0#
where
len :: [a] -> Int# -> Int
len [] a# = I# a#
len (_:xs) a# = len xs (a# +# 1#)
filter :: (a -> Bool) -> [a] -> [a]
filter _pred [] = []
filter pred (x:xs)
| pred x = x : filter pred xs
| otherwise = filter pred xs
filterFB :: (a -> b -> b) -> (a -> Bool) -> a -> b -> b
filterFB c p x r | p x = x `c` r
| otherwise = r
foldl :: (a -> b -> a) -> a -> [b] -> a
foldl f z0 xs0 = lgo z0 xs0
where
lgo z [] = z
lgo z (x:xs) = lgo (f z x) xs
scanl :: (a -> b -> a) -> a -> [b] -> [a]
scanl f q ls = q : (case ls of
[] -> []
x:xs -> scanl f (f q x) xs)
scanl1 :: (a -> a -> a) -> [a] -> [a]
scanl1 f (x:xs) = scanl f x xs
scanl1 _ [] = []
foldr1 :: (a -> a -> a) -> [a] -> a
foldr1 _ [x] = x
foldr1 f (x:xs) = f x (foldr1 f xs)
foldr1 _ [] = errorEmptyList "foldr1"
scanr :: (a -> b -> b) -> b -> [a] -> [b]
scanr _ q0 [] = [q0]
scanr f q0 (x:xs) = f x q : qs
where qs@(q:_) = scanr f q0 xs
scanr1 :: (a -> a -> a) -> [a] -> [a]
scanr1 _ [] = []
scanr1 _ [x] = [x]
scanr1 f (x:xs) = f x q : qs
where qs@(q:_) = scanr1 f xs
iterate :: (a -> a) -> a -> [a]
iterate f x = x : iterate f (f x)
iterateFB :: (a -> b -> b) -> (a -> a) -> a -> b
iterateFB c f x = x `c` iterateFB c f (f x)
repeat :: a -> [a]
repeat x = xs where xs = x : xs
repeatFB :: (a -> b -> b) -> a -> b
repeatFB c x = xs where xs = x `c` xs
replicate :: Int -> a -> [a]
replicate n x = take n (repeat x)
cycle :: [a] -> [a]
cycle [] = error "Prelude.cycle: empty list"
cycle xs = xs' where xs' = xs ++ xs'
takeWhile :: (a -> Bool) -> [a] -> [a]
takeWhile _ [] = []
takeWhile p (x:xs)
| p x = x : takeWhile p xs
| otherwise = []
dropWhile :: (a -> Bool) -> [a] -> [a]
dropWhile _ [] = []
dropWhile p xs@(x:xs')
| p x = dropWhile p xs'
| otherwise = xs
take :: Int -> [a] -> [a]
drop :: Int -> [a] -> [a]
splitAt :: Int -> [a] -> ([a],[a])
#ifdef USE_REPORT_PRELUDE
take n _ | n <= 0 = []
take _ [] = []
take n (x:xs) = x : take (n1) xs
drop n xs | n <= 0 = xs
drop _ [] = []
drop n (_:xs) = drop (n1) xs
splitAt n xs = (take n xs, drop n xs)
#else /* hack away */
takeFoldr :: Int -> [a] -> [a]
takeFoldr (I# n#) xs
= build (\c nil -> if n# <=# 0# then nil else
foldr (takeFB c nil) (takeConst nil) xs n#)
takeConst :: a -> Int# -> a
takeConst x _ = x
takeFB :: (a -> b -> b) -> b -> a -> (Int# -> b) -> Int# -> b
takeFB c n x xs m | m <=# 1# = x `c` n
| otherwise = x `c` xs (m -# 1#)
take (I# n#) xs = takeUInt n# xs
takeUInt :: Int# -> [b] -> [b]
takeUInt n xs
| n >=# 0# = take_unsafe_UInt n xs
| otherwise = []
take_unsafe_UInt :: Int# -> [b] -> [b]
take_unsafe_UInt 0# _ = []
take_unsafe_UInt m ls =
case ls of
[] -> []
(x:xs) -> x : take_unsafe_UInt (m -# 1#) xs
takeUInt_append :: Int# -> [b] -> [b] -> [b]
takeUInt_append n xs rs
| n >=# 0# = take_unsafe_UInt_append n xs rs
| otherwise = []
take_unsafe_UInt_append :: Int# -> [b] -> [b] -> [b]
take_unsafe_UInt_append 0# _ rs = rs
take_unsafe_UInt_append m ls rs =
case ls of
[] -> rs
(x:xs) -> x : take_unsafe_UInt_append (m -# 1#) xs rs
drop (I# n#) ls
| n# <# 0# = ls
| otherwise = drop# n# ls
where
drop# :: Int# -> [a] -> [a]
drop# 0# xs = xs
drop# _ xs@[] = xs
drop# m# (_:xs) = drop# (m# -# 1#) xs
splitAt (I# n#) ls
| n# <# 0# = ([], ls)
| otherwise = splitAt# n# ls
where
splitAt# :: Int# -> [a] -> ([a], [a])
splitAt# 0# xs = ([], xs)
splitAt# _ xs@[] = (xs, xs)
splitAt# m# (x:xs) = (x:xs', xs'')
where
(xs', xs'') = splitAt# (m# -# 1#) xs
#endif /* USE_REPORT_PRELUDE */
span :: (a -> Bool) -> [a] -> ([a],[a])
span _ xs@[] = (xs, xs)
span p xs@(x:xs')
| p x = let (ys,zs) = span p xs' in (x:ys,zs)
| otherwise = ([],xs)
break :: (a -> Bool) -> [a] -> ([a],[a])
#ifdef USE_REPORT_PRELUDE
break p = span (not . p)
#else
break _ xs@[] = (xs, xs)
break p xs@(x:xs')
| p x = ([],xs)
| otherwise = let (ys,zs) = break p xs' in (x:ys,zs)
#endif
reverse :: [a] -> [a]
#ifdef USE_REPORT_PRELUDE
reverse = foldl (flip (:)) []
#else
reverse l = rev l []
where
rev [] a = a
rev (x:xs) a = rev xs (x:a)
#endif
and :: [Bool] -> Bool
or :: [Bool] -> Bool
#ifdef USE_REPORT_PRELUDE
and = foldr (&&) True
or = foldr (||) False
#else
and [] = True
and (x:xs) = x && and xs
or [] = False
or (x:xs) = x || or xs
#endif
any :: (a -> Bool) -> [a] -> Bool
all :: (a -> Bool) -> [a] -> Bool
#ifdef USE_REPORT_PRELUDE
any p = or . map p
all p = and . map p
#else
any _ [] = False
any p (x:xs) = p x || any p xs
all _ [] = True
all p (x:xs) = p x && all p xs
#endif
elem :: (Eq a) => a -> [a] -> Bool
notElem :: (Eq a) => a -> [a] -> Bool
#ifdef USE_REPORT_PRELUDE
elem x = any (== x)
notElem x = all (/= x)
#else
elem _ [] = False
elem x (y:ys) = x==y || elem x ys
notElem _ [] = True
notElem x (y:ys)= x /= y && notElem x ys
#endif
lookup :: (Eq a) => a -> [(a,b)] -> Maybe b
lookup _key [] = Nothing
lookup key ((x,y):xys)
| key == x = Just y
| otherwise = lookup key xys
concatMap :: (a -> [b]) -> [a] -> [b]
concatMap f = foldr ((++) . f) []
concat :: [[a]] -> [a]
concat = foldr (++) []
\end{code} \begin{code}
(!!) :: [a] -> Int -> a
#ifdef USE_REPORT_PRELUDE
xs !! n | n < 0 = error "Prelude.!!: negative index"
[] !! _ = error "Prelude.!!: index too large"
(x:_) !! 0 = x
(_:xs) !! n = xs !! (n1)
#else
xs !! (I# n0) | n0 <# 0# = error "Prelude.(!!): negative index\n"
| otherwise = sub xs n0
where
sub :: [a] -> Int# -> a
sub [] _ = error "Prelude.(!!): index too large\n"
sub (y:ys) n = if n ==# 0#
then y
else sub ys (n -# 1#)
#endif
\end{code} %********************************************************* %* * \subsection{The zip family} %* * %********************************************************* \begin{code}
foldr2 :: (a -> b -> c -> c) -> c -> [a] -> [b] -> c foldr2 _k z [] _ys = z foldr2 _k z _xs [] = z foldr2 k z (x:xs) (y:ys) = k x y (foldr2 k z xs ys) foldr2_left :: (a -> b -> c -> d) -> d -> a -> ([b] -> c) -> [b] -> d foldr2_left _k z _x _r [] = z foldr2_left k _z x r (y:ys) = k x y (r ys) foldr2_right :: (a -> b -> c -> d) -> d -> b -> ([a] -> c) -> [a] -> d foldr2_right _k z _y _r [] = z foldr2_right k _z y r (x:xs) = k x y (r xs)\end{code} The foldr2/right rule isn't exactly right, because it changes the strictness of foldr2 (and thereby zip) E.g. main = print (null (zip nonobviousNil (build undefined))) where nonobviousNil = f 3 f n = if n == 0 then [] else f (n-1) I'm going to leave it though. Zips for larger tuples are in the List module. \begin{code}
zip :: [a] -> [b] -> [(a,b)] zip (a:as) (b:bs) = (a,b) : zip as bs zip _ _ = [] zipFB :: ((a, b) -> c -> d) -> a -> b -> c -> d zipFB c = \x y r -> (x,y) `c` r\end{code} \begin{code}
zip3 :: [a] -> [b] -> [c] -> [(a,b,c)] zip3 (a:as) (b:bs) (c:cs) = (a,b,c) : zip3 as bs cs zip3 _ _ _ = []\end{code} -- The zipWith family generalises the zip family by zipping with the -- function given as the first argument, instead of a tupling function. \begin{code}
zipWith :: (a->b->c) -> [a]->[b]->[c] zipWith f (a:as) (b:bs) = f a b : zipWith f as bs zipWith _ _ _ = [] zipWithFB :: (a -> b -> c) -> (d -> e -> a) -> d -> e -> b -> c zipWithFB c f = \x y r -> (x `f` y) `c` r\end{code} \begin{code}
zipWith3 :: (a->b->c->d) -> [a]->[b]->[c]->[d]
zipWith3 z (a:as) (b:bs) (c:cs)
= z a b c : zipWith3 z as bs cs
zipWith3 _ _ _ _ = []
unzip :: [(a,b)] -> ([a],[b])
unzip = foldr (\(a,b) ~(as,bs) -> (a:as,b:bs)) ([],[])
unzip3 :: [(a,b,c)] -> ([a],[b],[c])
unzip3 = foldr (\(a,b,c) ~(as,bs,cs) -> (a:as,b:bs,c:cs))
([],[],[])
\end{code} %********************************************************* %* * \subsection{Error code} %* * %********************************************************* Common up near identical calls to `error' to reduce the number constant strings created when compiled: \begin{code}
errorEmptyList :: String -> a errorEmptyList fun = error (prel_list_str ++ fun ++ ": empty list") prel_list_str :: String prel_list_str = "Prelude."\end{code}
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