Haskell Hierarchical Libraries (base package)ContentsIndex
GHC.List
Portability non-portable (GHC Extensions)
Stability internal
Maintainer cvs-ghc@haskell.org
Description
The List data type and its operations
Synopsis
map :: (a -> b) -> [a] -> [b]
(++) :: [a] -> [a] -> [a]
filter :: (a -> Bool) -> [a] -> [a]
concat :: [[a]] -> [a]
head :: [a] -> a
last :: [a] -> a
tail :: [a] -> [a]
init :: [a] -> [a]
null :: [a] -> Bool
length :: [a] -> Int
(!!) :: [a] -> Int -> a
foldl :: (a -> b -> a) -> a -> [b] -> a
foldl1 :: (a -> a -> a) -> [a] -> a
scanl :: (a -> b -> a) -> a -> [b] -> [a]
scanl1 :: (a -> a -> a) -> [a] -> [a]
foldr :: (a -> b -> b) -> b -> [a] -> b
foldr1 :: (a -> a -> a) -> [a] -> a
scanr :: (a -> b -> b) -> b -> [a] -> [b]
scanr1 :: (a -> a -> a) -> [a] -> [a]
iterate :: (a -> a) -> a -> [a]
repeat :: a -> [a]
replicate :: Int -> a -> [a]
cycle :: [a] -> [a]
take :: Int -> [a] -> [a]
drop :: Int -> [a] -> [a]
splitAt :: Int -> [a] -> ([a], [a])
takeWhile :: (a -> Bool) -> [a] -> [a]
dropWhile :: (a -> Bool) -> [a] -> [a]
span :: (a -> Bool) -> [a] -> ([a], [a])
break :: (a -> Bool) -> [a] -> ([a], [a])
reverse :: [a] -> [a]
and :: [Bool] -> Bool
or :: [Bool] -> Bool
any :: (a -> Bool) -> [a] -> Bool
all :: (a -> Bool) -> [a] -> Bool
elem :: Eq a => a -> [a] -> Bool
notElem :: Eq a => a -> [a] -> Bool
lookup :: Eq a => a -> [(a, b)] -> Maybe b
maximum :: Ord a => [a] -> a
minimum :: Ord a => [a] -> a
concatMap :: (a -> [b]) -> [a] -> [b]
zip :: [a] -> [b] -> [(a, b)]
zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
unzip :: [(a, b)] -> ([a], [b])
unzip3 :: [(a, b, c)] -> ([a], [b], [c])
takeUInt_append :: Int# -> [b] -> [b] -> [b]
Documentation
map :: (a -> b) -> [a] -> [b]

map f xs is the list obtained by applying f to each element of xs, i.e.,

 map f [x1, x2, ..., xn] == [f x1, f x2, ..., f xn]
 map f [x1, x2, ...] == [f x1, f x2, ...]
(++) :: [a] -> [a] -> [a]

Append two lists, i.e.,

 [x1, ..., xm] ++ [y1, ..., yn] == [x1, ..., xm, y1, ..., yn]
 [x1, ..., xm] ++ [y1, ...] == [x1, ..., xm, y1, ...]

If the first list is not finite, the result is the first list.

filter :: (a -> Bool) -> [a] -> [a]

filter, applied to a predicate and a list, returns the list of those elements that satisfy the predicate; i.e.,

 filter p xs = [ x | x <- xs, p x]
concat :: [[a]] -> [a]
Concatenate a list of lists.
head :: [a] -> a
Extract the first element of a list, which must be non-empty.
last :: [a] -> a
Extract the last element of a list, which must be finite and non-empty.
tail :: [a] -> [a]
Extract the elements after the head of a list, which must be non-empty.
init :: [a] -> [a]
Return all the elements of a list except the last one. The list must be finite and non-empty.
null :: [a] -> Bool
Test whether a list is empty.
length :: [a] -> Int
length returns the length of a finite list as an Int. It is an instance of the more general genericLength, the result type of which may be any kind of number.
(!!) :: [a] -> Int -> a
List index (subscript) operator, starting from 0. It is an instance of the more general genericIndex, which takes an index of any integral type.
foldl :: (a -> b -> a) -> a -> [b] -> a

foldl, applied to a binary operator, a starting value (typically the left-identity of the operator), and a list, reduces the list using the binary operator, from left to right:

 foldl f z [x1, x2, ..., xn] == (...((z `f` x1) `f` x2) `f`...) `f` xn

The list must be finite.

foldl1 :: (a -> a -> a) -> [a] -> a
foldl1 is a variant of foldl that has no starting value argument, and thus must be applied to non-empty lists.
scanl :: (a -> b -> a) -> a -> [b] -> [a]

scanl is similar to foldl, but returns a list of successive reduced values from the left:

 scanl f z [x1, x2, ...] == [z, z `f` x1, (z `f` x1) `f` x2, ...]

Note that

 last (scanl f z xs) == foldl f z xs.
scanl1 :: (a -> a -> a) -> [a] -> [a]

scanl1 is a variant of scanl that has no starting value argument:

 scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
foldr :: (a -> b -> b) -> b -> [a] -> b

foldr, applied to a binary operator, a starting value (typically the right-identity of the operator), and a list, reduces the list using the binary operator, from right to left:

 foldr f z [x1, x2, ..., xn] == x1 `f` (x2 `f` ... (xn `f` z)...)
foldr1 :: (a -> a -> a) -> [a] -> a
foldr1 is a variant of foldr that has no starting value argument, and thus must be applied to non-empty lists.
scanr :: (a -> b -> b) -> b -> [a] -> [b]

scanr is the right-to-left dual of scanl. Note that

 head (scanr f z xs) == foldr f z xs.
scanr1 :: (a -> a -> a) -> [a] -> [a]
scanr1 is a variant of scanr that has no starting value argument.
iterate :: (a -> a) -> a -> [a]

iterate f x returns an infinite list of repeated applications of f to x:

 iterate f x == [x, f x, f (f x), ...]
repeat :: a -> [a]
repeat x is an infinite list, with x the value of every element.
replicate :: Int -> a -> [a]
replicate n x is a list of length n with x the value of every element. It is an instance of the more general genericReplicate, in which n may be of any integral type.
cycle :: [a] -> [a]
cycle ties a finite list into a circular one, or equivalently, the infinite repetition of the original list. It is the identity on infinite lists.
take :: Int -> [a] -> [a]
take n, applied to a list xs, returns the prefix of xs of length n, or xs itself if n > length xs. It is an instance of the more general genericTake, in which n may be of any integral type.
drop :: Int -> [a] -> [a]
drop n xs returns the suffix of xs after the first n elements, or [] if n > length xs. It is an instance of the more general genericDrop, in which n may be of any integral type.
splitAt :: Int -> [a] -> ([a], [a])
splitAt n xs is equivalent to (take n xs, drop n xs). It is an instance of the more general genericSplitAt, in which n may be of any integral type.
takeWhile :: (a -> Bool) -> [a] -> [a]
takeWhile, applied to a predicate p and a list xs, returns the longest prefix (possibly empty) of xs of elements that satisfy p.
dropWhile :: (a -> Bool) -> [a] -> [a]
dropWhile p xs returns the suffix remaining after takeWhile p xs.
span :: (a -> Bool) -> [a] -> ([a], [a])
span p xs is equivalent to (takeWhile p xs, dropWhile p xs)
break :: (a -> Bool) -> [a] -> ([a], [a])
break p is equivalent to span (not . p).
reverse :: [a] -> [a]
reverse xs returns the elements of xs in reverse order. xs must be finite.
and :: [Bool] -> Bool
and returns the conjunction of a Boolean list. For the result to be True, the list must be finite; False, however, results from a False value at a finite index of a finite or infinite list.
or :: [Bool] -> Bool
or returns the disjunction of a Boolean list. For the result to be False, the list must be finite; True, however, results from a True value at a finite index of a finite or infinite list.
any :: (a -> Bool) -> [a] -> Bool
Applied to a predicate and a list, any determines if any element of the list satisfies the predicate.
all :: (a -> Bool) -> [a] -> Bool
Applied to a predicate and a list, all determines if all elements of the list satisfy the predicate.
elem :: Eq a => a -> [a] -> Bool
elem is the list membership predicate, usually written in infix form, e.g., x elem xs.
notElem :: Eq a => a -> [a] -> Bool
notElem is the negation of elem.
lookup :: Eq a => a -> [(a, b)] -> Maybe b
lookup key assocs looks up a key in an association list.
maximum :: Ord a => [a] -> a
maximum returns the maximum value from a list, which must be non-empty, finite, and of an ordered type. It is a special case of maximumBy, which allows the programmer to supply their own comparison function.
minimum :: Ord a => [a] -> a
minimum returns the minimum value from a list, which must be non-empty, finite, and of an ordered type. It is a special case of minimumBy, which allows the programmer to supply their own comparison function.
concatMap :: (a -> [b]) -> [a] -> [b]
Map a function over a list and concatenate the results.
zip :: [a] -> [b] -> [(a, b)]
zip takes two lists and returns a list of corresponding pairs. If one input list is short, excess elements of the longer list are discarded.
zip3 :: [a] -> [b] -> [c] -> [(a, b, c)]
zip3 takes three lists and returns a list of triples, analogous to zip.
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c]
zipWith generalises zip by zipping with the function given as the first argument, instead of a tupling function. For example, zipWith (+) is applied to two lists to produce the list of corresponding sums.
zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d]
The zipWith3 function takes a function which combines three elements, as well as three lists and returns a list of their point-wise combination, analogous to zipWith.
unzip :: [(a, b)] -> ([a], [b])
unzip transforms a list of pairs into a list of first components and a list of second components.
unzip3 :: [(a, b, c)] -> ([a], [b], [c])
The unzip3 function takes a list of triples and returns three lists, analogous to unzip.
takeUInt_append :: Int# -> [b] -> [b] -> [b]
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