\begin{code}
-{-# OPTIONS_GHC -fno-implicit-prelude #-}
+{-# LANGUAGE CPP, NoImplicitPrelude, MagicHash #-}
{-# OPTIONS_HADDOCK hide #-}
+
-----------------------------------------------------------------------------
-- |
-- Module : GHC.List
) where
-import Data.Tuple() -- Instances
import Data.Maybe
import GHC.Base
head (x:_) = x
head [] = badHead
+badHead :: a
badHead = errorEmptyList "head"
-- This rule is useful in cases like
#endif
-- | Return all the elements of a list except the last one.
--- The list must be finite and non-empty.
+-- The list must be non-empty.
init :: [a] -> [a]
#ifdef USE_REPORT_PRELUDE
init [x] = []
null [] = True
null (_:_) = False
--- | 'length' returns the length of a finite list as an 'Int'.
+-- | /O(n)/. 'length' returns the length of a finite list as an 'Int'.
-- It is an instance of the more general 'Data.List.genericLength',
-- the result type of which may be any kind of number.
length :: [a] -> Int
| otherwise = filter pred xs
{-# NOINLINE [0] filterFB #-}
+filterFB :: (a -> b -> b) -> (a -> Bool) -> a -> b -> b
filterFB c p x r | p x = x `c` r
| otherwise = r
-- and hence the classic space leak on foldl (+) 0 xs
foldl :: (a -> b -> a) -> a -> [b] -> a
-foldl f z xs = lgo z xs
+foldl f z0 xs0 = lgo z0 xs0
where
lgo z [] = z
lgo z (x:xs) = lgo (f z x) xs
-- | 'scanr1' is a variant of 'scanr' that has no starting value argument.
scanr1 :: (a -> a -> a) -> [a] -> [a]
-scanr1 f [] = []
-scanr1 f [x] = [x]
+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 x = xs where xs = x : xs
{-# INLINE [0] repeatFB #-} -- ditto
+repeatFB :: (a -> b -> b) -> a -> b
repeatFB c x = xs where xs = x `c` xs
#endif
-- | Applied to a predicate and a list, 'any' determines if any element
--- of the list satisfies the predicate.
+-- of the list satisfies the predicate. For the result to be
+-- 'False', the list must be finite; 'True', however, results from a 'True'
+-- value for the predicate applied to an element at a finite index of a finite or infinite list.
any :: (a -> Bool) -> [a] -> Bool
-- | Applied to a predicate and a list, 'all' determines if all elements
--- of the list satisfy the predicate.
+-- of the list satisfy the predicate. For the result to be
+-- 'True', the list must be finite; 'False', however, results from a 'False'
+-- value for the predicate applied to an element at a finite index of a finite or infinite list.
all :: (a -> Bool) -> [a] -> Bool
#ifdef USE_REPORT_PRELUDE
any p = or . map p
#endif
-- | 'elem' is the list membership predicate, usually written in infix form,
--- e.g., @x \`elem\` xs@.
+-- e.g., @x \`elem\` xs@. For the result to be
+-- 'False', the list must be finite; 'True', however, results from an element equal to @x@ found at a finite index of a finite or infinite list.
elem :: (Eq a) => a -> [a] -> Bool
-- | 'notElem' is the negation of 'elem'.
-- The semantics is not quite the same for error conditions
-- in the more efficient version.
--
-xs !! (I# n) | n <# 0# = error "Prelude.(!!): negative index\n"
- | otherwise = sub xs n
+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"
%*********************************************************
\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)
zip _ _ = []
{-# INLINE [0] zipFB #-}
-zipFB c x y r = (x,y) `c` r
+zipFB :: ((a, b) -> c -> d) -> a -> b -> c -> d
+zipFB c = \x y r -> (x,y) `c` r
{-# RULES
"zip" [~1] forall xs ys. zip xs ys = build (\c n -> foldr2 (zipFB c) n xs ys)
zipWith f (a:as) (b:bs) = f a b : zipWith f as bs
zipWith _ _ _ = []
+-- zipWithFB must have arity 2 since it gets two arguments in the "zipWith"
+-- rule; it might not get inlined otherwise
{-# INLINE [0] zipWithFB #-}
-zipWithFB c f x y r = (x `f` y) `c` r
+zipWithFB :: (a -> b -> c) -> (d -> e -> a) -> d -> e -> b -> c
+zipWithFB c f = \x y r -> (x `f` y) `c` r
{-# RULES
"zipWith" [~1] forall f xs ys. zipWith f xs ys = build (\c n -> foldr2 (zipWithFB c f) n xs ys)
projects / ghc-base.git / blobdiff