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| GHC.List | | Portability | non-portable (GHC Extensions) | | Stability | internal | | Maintainer | cvs-ghc@haskell.org |
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| Description |
| The List data type and its operations
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| Synopsis |
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| 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] |
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| Documentation |
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| 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, ...] |
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| (++) :: [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. |
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| 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] |
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| concat :: [[a]] -> [a] |
| Concatenate a list of lists. |
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| head :: [a] -> a |
| Extract the first element of a list, which must be non-empty. |
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| last :: [a] -> a |
| Extract the last element of a list, which must be finite and non-empty. |
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| tail :: [a] -> [a] |
| Extract the elements after the head of a list, which must be non-empty. |
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| init :: [a] -> [a] |
| Return all the elements of a list except the last one.
The list must be finite and non-empty. |
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| null :: [a] -> Bool |
| Test whether a list is empty. |
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| 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. |
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| (!!) :: [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. |
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| 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. |
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| 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. |
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| 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. |
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| 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, ...] |
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| 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)...) |
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| 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. |
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| 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. |
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| scanr1 :: (a -> a -> a) -> [a] -> [a] |
| scanr1 is a variant of scanr that has no starting value argument. |
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| 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), ...] |
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| repeat :: a -> [a] |
| repeat x is an infinite list, with x the value of every element. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| 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. |
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| dropWhile :: (a -> Bool) -> [a] -> [a] |
| dropWhile p xs returns the suffix remaining after takeWhile p xs. |
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| span :: (a -> Bool) -> [a] -> ([a], [a]) |
| span p xs is equivalent to (takeWhile p xs, dropWhile p xs) |
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| break :: (a -> Bool) -> [a] -> ([a], [a]) |
| break p is equivalent to span (not . p). |
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| reverse :: [a] -> [a] |
| reverse xs returns the elements of xs in reverse order.
xs must be finite. |
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| 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. |
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| 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. |
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| any :: (a -> Bool) -> [a] -> Bool |
| Applied to a predicate and a list, any determines if any element
of the list satisfies the predicate. |
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| all :: (a -> Bool) -> [a] -> Bool |
| Applied to a predicate and a list, all determines if all elements
of the list satisfy the predicate. |
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| elem :: Eq a => a -> [a] -> Bool |
| elem is the list membership predicate, usually written in infix form,
e.g., x elem xs. |
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| notElem :: Eq a => a -> [a] -> Bool |
| notElem is the negation of elem. |
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| lookup :: Eq a => a -> [(a, b)] -> Maybe b |
| lookup key assocs looks up a key in an association list. |
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| 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. |
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| 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. |
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| concatMap :: (a -> [b]) -> [a] -> [b] |
| Map a function over a list and concatenate the results. |
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| 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. |
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| zip3 :: [a] -> [b] -> [c] -> [(a, b, c)] |
| zip3 takes three lists and returns a list of triples, analogous to
zip. |
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| 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. |
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| 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. |
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| unzip :: [(a, b)] -> ([a], [b]) |
| unzip transforms a list of pairs into a list of first components
and a list of second components. |
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| unzip3 :: [(a, b, c)] -> ([a], [b], [c]) |
| The unzip3 function takes a list of triples and returns three
lists, analogous to unzip. |
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| takeUInt_append :: Int# -> [b] -> [b] -> [b] |
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| Produced by Haddock version 0.6 |
