Copyright | (c) The University of Glasgow 2001 |
---|---|
License | BSD-style (see the file libraries/base/LICENSE) |
Maintainer | [email protected] |
Stability | stable |
Portability | portable |
Safe Haskell | Trustworthy |
Language | Haskell2010 |
Operations on lists.
(++) :: [a] -> [a] -> [a] infixr 5 Source
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.
Extract the first element of a list, which must be non-empty.
Extract the last element of a list, which must be finite and non-empty.
Extract the elements after the head of a list, which must be non-empty.
Return all the elements of a list except the last one. The list must be non-empty.
uncons :: [a] -> Maybe (a, [a]) Source
Decompose a list into its head and tail. If the list is empty, returns Nothing
. If the list is non-empty, returns Just (x, xs)
, where x
is the head of the list and xs
its tail.
Since: 4.8.0.0
null :: Foldable t => t a -> Bool Source
Test whether the structure is empty. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
length :: Foldable t => t a -> Int Source
Returns the size/length of a finite structure as an Int
. The default implementation is optimized for structures that are similar to cons-lists, because there is no general way to do better.
map :: (a -> b) -> [a] -> [b] Source
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, ...]
reverse
xs
returns the elements of xs
in reverse order. xs
must be finite.
intersperse :: a -> [a] -> [a] Source
The intersperse
function takes an element and a list and `intersperses' that element between the elements of the list. For example,
intersperse ',' "abcde" == "a,b,c,d,e"
intercalate :: [a] -> [[a]] -> [a] Source
intercalate
xs xss
is equivalent to (concat (intersperse xs xss))
. It inserts the list xs
in between the lists in xss
and concatenates the result.
transpose :: [[a]] -> [[a]] Source
The transpose
function transposes the rows and columns of its argument. For example,
transpose [[1,2,3],[4,5,6]] == [[1,4],[2,5],[3,6]]
If some of the rows are shorter than the following rows, their elements are skipped:
transpose [[10,11],[20],[],[30,31,32]] == [[10,20,30],[11,31],[32]]
subsequences :: [a] -> [[a]] Source
The subsequences
function returns the list of all subsequences of the argument.
subsequences "abc" == ["","a","b","ab","c","ac","bc","abc"]
permutations :: [a] -> [[a]] Source
The permutations
function returns the list of all permutations of the argument.
permutations "abc" == ["abc","bac","cba","bca","cab","acb"]
foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b Source
Left-associative fold of a structure.
In the case of lists, foldl
, when 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
Note that to produce the outermost application of the operator the entire input list must be traversed. This means that foldl'
will diverge if given an infinite list.
Also note that if you want an efficient left-fold, you probably want to use foldl'
instead of foldl
. The reason for this is that latter does not force the "inner" results (e.g. z f x1
in the above example) before applying them to the operator (e.g. to (f x2)
). This results in a thunk chain O(n)
elements long, which then must be evaluated from the outside-in.
For a general Foldable
structure this should be semantically identical to,
foldl f z =foldl
f z .toList
foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b Source
Left-associative fold of a structure but with strict application of the operator.
This ensures that each step of the fold is forced to weak head normal form before being applied, avoiding the collection of thunks that would otherwise occur. This is often what you want to strictly reduce a finite list to a single, monolithic result (e.g. length
).
For a general Foldable
structure this should be semantically identical to,
foldl f z =foldl'
f z .toList
foldl1 :: Foldable t => (a -> a -> a) -> t a -> a Source
A variant of foldl
that has no base case, and thus may only be applied to non-empty structures.
foldl1
f =foldl1
f .toList
foldl1' :: (a -> a -> a) -> [a] -> a Source
A strict version of foldl1
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b Source
Right-associative fold of a structure.
In the case of lists, foldr
, when 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)...)
Note that, since the head of the resulting expression is produced by an application of the operator to the first element of the list, foldr
can produce a terminating expression from an infinite list.
For a general Foldable
structure this should be semantically identical to,
foldr f z =foldr
f z .toList
foldr1 :: Foldable t => (a -> a -> a) -> t a -> a Source
A variant of foldr
that has no base case, and thus may only be applied to non-empty structures.
foldr1
f =foldr1
f .toList
concat :: Foldable t => t [a] -> [a] Source
The concatenation of all the elements of a container of lists.
concatMap :: Foldable t => (a -> [b]) -> t a -> [b] Source
Map a function over all the elements of a container and concatenate the resulting lists.
and :: Foldable t => t Bool -> Bool Source
and
returns the conjunction of a container of Bools. For the result to be True
, the container must be finite; False
, however, results from a False
value finitely far from the left end.
or :: Foldable t => t Bool -> Bool Source
or
returns the disjunction of a container of Bools. For the result to be False
, the container must be finite; True
, however, results from a True
value finitely far from the left end.
any :: Foldable t => (a -> Bool) -> t a -> Bool Source
Determines whether any element of the structure satisfies the predicate.
all :: Foldable t => (a -> Bool) -> t a -> Bool Source
Determines whether all elements of the structure satisfy the predicate.
sum :: (Foldable t, Num a) => t a -> a Source
The sum
function computes the sum of the numbers of a structure.
product :: (Foldable t, Num a) => t a -> a Source
The product
function computes the product of the numbers of a structure.
maximum :: forall a. (Foldable t, Ord a) => t a -> a Source
The largest element of a non-empty structure.
minimum :: forall a. (Foldable t, Ord a) => t a -> a Source
The least element of a non-empty structure.
scanl :: (b -> a -> b) -> b -> [a] -> [b] Source
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.
scanl' :: (b -> a -> b) -> b -> [a] -> [b] Source
A strictly accumulating version of scanl
scanl1 :: (a -> a -> a) -> [a] -> [a] Source
scanl1
is a variant of scanl
that has no starting value argument:
scanl1 f [x1, x2, ...] == [x1, x1 `f` x2, ...]
scanr :: (a -> b -> b) -> b -> [a] -> [b] Source
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] Source
scanr1
is a variant of scanr
that has no starting value argument.
mapAccumL :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) Source
The mapAccumL
function behaves like a combination of fmap
and foldl
; it applies a function to each element of a structure, passing an accumulating parameter from left to right, and returning a final value of this accumulator together with the new structure.
mapAccumR :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) Source
The mapAccumR
function behaves like a combination of fmap
and foldr
; it applies a function to each element of a structure, passing an accumulating parameter from right to left, and returning a final value of this accumulator together with the new structure.
iterate :: (a -> a) -> a -> [a] Source
iterate
f x
returns an infinite list of repeated applications of f
to x
:
iterate f x == [x, f x, f (f x), ...]
repeat
x
is an infinite list, with x
the value of every element.
replicate :: Int -> a -> [a] Source
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
ties a finite list into a circular one, or equivalently, the infinite repetition of the original list. It is the identity on infinite lists.
unfoldr :: (b -> Maybe (a, b)) -> b -> [a] Source
The unfoldr
function is a `dual' to foldr
: while foldr
reduces a list to a summary value, unfoldr
builds a list from a seed value. The function takes the element and returns Nothing
if it is done producing the list or returns Just
(a,b)
, in which case, a
is a prepended to the list and b
is used as the next element in a recursive call. For example,
iterate f == unfoldr (\x -> Just (x, f x))
In some cases, unfoldr
can undo a foldr
operation:
unfoldr f' (foldr f z xs) == xs
if the following holds:
f' (f x y) = Just (x,y) f' z = Nothing
A simple use of unfoldr:
unfoldr (\b -> if b == 0 then Nothing else Just (b, b-1)) 10 [10,9,8,7,6,5,4,3,2,1]
take :: Int -> [a] -> [a] Source
take
n
, applied to a list xs
, returns the prefix of xs
of length n
, or xs
itself if n > length xs
:
take 5 "Hello World!" == "Hello" take 3 [1,2,3,4,5] == [1,2,3] take 3 [1,2] == [1,2] take 3 [] == [] take (-1) [1,2] == [] take 0 [1,2] == []
It is an instance of the more general genericTake
, in which n
may be of any integral type.
drop :: Int -> [a] -> [a] Source
drop
n xs
returns the suffix of xs
after the first n
elements, or []
if n > length xs
:
drop 6 "Hello World!" == "World!" drop 3 [1,2,3,4,5] == [4,5] drop 3 [1,2] == [] drop 3 [] == [] drop (-1) [1,2] == [1,2] drop 0 [1,2] == [1,2]
It is an instance of the more general genericDrop
, in which n
may be of any integral type.
splitAt :: Int -> [a] -> ([a], [a]) Source
splitAt
n xs
returns a tuple where first element is xs
prefix of length n
and second element is the remainder of the list:
splitAt 6 "Hello World!" == ("Hello ","World!") splitAt 3 [1,2,3,4,5] == ([1,2,3],[4,5]) splitAt 1 [1,2,3] == ([1],[2,3]) splitAt 3 [1,2,3] == ([1,2,3],[]) splitAt 4 [1,2,3] == ([1,2,3],[]) splitAt 0 [1,2,3] == ([],[1,2,3]) splitAt (-1) [1,2,3] == ([],[1,2,3])
It is equivalent to (take n xs, drop n xs)
when n
is not _|_
(splitAt _|_ xs = _|_
). splitAt
is an instance of the more general genericSplitAt
, in which n
may be of any integral type.
takeWhile :: (a -> Bool) -> [a] -> [a] Source
takeWhile
, applied to a predicate p
and a list xs
, returns the longest prefix (possibly empty) of xs
of elements that satisfy p
:
takeWhile (< 3) [1,2,3,4,1,2,3,4] == [1,2] takeWhile (< 9) [1,2,3] == [1,2,3] takeWhile (< 0) [1,2,3] == []
dropWhile :: (a -> Bool) -> [a] -> [a] Source
dropWhile
p xs
returns the suffix remaining after takeWhile
p xs
:
dropWhile (< 3) [1,2,3,4,5,1,2,3] == [3,4,5,1,2,3] dropWhile (< 9) [1,2,3] == [] dropWhile (< 0) [1,2,3] == [1,2,3]
dropWhileEnd :: (a -> Bool) -> [a] -> [a] Source
The dropWhileEnd
function drops the largest suffix of a list in which the given predicate holds for all elements. For example:
dropWhileEnd isSpace "foo\n" == "foo" dropWhileEnd isSpace "foo bar" == "foo bar" dropWhileEnd isSpace ("foo\n" ++ undefined) == "foo" ++ undefined
Since: 4.5.0.0
span :: (a -> Bool) -> [a] -> ([a], [a]) Source
span
, applied to a predicate p
and a list xs
, returns a tuple where first element is longest prefix (possibly empty) of xs
of elements that satisfy p
and second element is the remainder of the list:
span (< 3) [1,2,3,4,1,2,3,4] == ([1,2],[3,4,1,2,3,4]) span (< 9) [1,2,3] == ([1,2,3],[]) span (< 0) [1,2,3] == ([],[1,2,3])
span
p xs
is equivalent to (takeWhile p xs, dropWhile p xs)
break :: (a -> Bool) -> [a] -> ([a], [a]) Source
break
, applied to a predicate p
and a list xs
, returns a tuple where first element is longest prefix (possibly empty) of xs
of elements that do not satisfy p
and second element is the remainder of the list:
break (> 3) [1,2,3,4,1,2,3,4] == ([1,2,3],[4,1,2,3,4]) break (< 9) [1,2,3] == ([],[1,2,3]) break (> 9) [1,2,3] == ([1,2,3],[])
break
p
is equivalent to span (not . p)
.
stripPrefix :: Eq a => [a] -> [a] -> Maybe [a] Source
The stripPrefix
function drops the given prefix from a list. It returns Nothing
if the list did not start with the prefix given, or Just
the list after the prefix, if it does.
stripPrefix "foo" "foobar" == Just "bar" stripPrefix "foo" "foo" == Just "" stripPrefix "foo" "barfoo" == Nothing stripPrefix "foo" "barfoobaz" == Nothing
group :: Eq a => [a] -> [[a]] Source
The group
function takes a list and returns a list of lists such that the concatenation of the result is equal to the argument. Moreover, each sublist in the result contains only equal elements. For example,
group "Mississippi" = ["M","i","ss","i","ss","i","pp","i"]
It is a special case of groupBy
, which allows the programmer to supply their own equality test.
The inits
function returns all initial segments of the argument, shortest first. For example,
inits "abc" == ["","a","ab","abc"]
Note that inits
has the following strictness property: inits (xs ++ _|_) = inits xs ++ _|_
In particular, inits _|_ = [] : _|_
The tails
function returns all final segments of the argument, longest first. For example,
tails "abc" == ["abc", "bc", "c",""]
Note that tails
has the following strictness property: tails _|_ = _|_ : _|_
isPrefixOf :: Eq a => [a] -> [a] -> Bool Source
The isPrefixOf
function takes two lists and returns True
iff the first list is a prefix of the second.
isSuffixOf :: Eq a => [a] -> [a] -> Bool Source
The isSuffixOf
function takes two lists and returns True
iff the first list is a suffix of the second. The second list must be finite.
isInfixOf :: Eq a => [a] -> [a] -> Bool Source
The isInfixOf
function takes two lists and returns True
iff the first list is contained, wholly and intact, anywhere within the second.
Example:
isInfixOf "Haskell" "I really like Haskell." == True isInfixOf "Ial" "I really like Haskell." == False
isSubsequenceOf :: Eq a => [a] -> [a] -> Bool Source
The isSubsequenceOf
function takes two lists and returns True
if all the elements of the first list occur, in order, in the second. The elements do not have to occur consecutively.
isSubsequenceOf x y
is equivalent to elem x (subsequences y)
.
>>>
isSubsequenceOf "GHC" "The Glorious Haskell Compiler"
True>>>
isSubsequenceOf ['a','d'..'z'] ['a'..'z']
True>>>
isSubsequenceOf [1..10] [10,9..0]
False
Since: 4.8.0.0
elem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 Source
Does the element occur in the structure?
notElem :: (Foldable t, Eq a) => a -> t a -> Bool infix 4 Source
notElem
is the negation of elem
.
lookup :: Eq a => a -> [(a, b)] -> Maybe b Source
lookup
key assocs
looks up a key in an association list.
find :: Foldable t => (a -> Bool) -> t a -> Maybe a Source
The find
function takes a predicate and a structure and returns the leftmost element of the structure matching the predicate, or Nothing
if there is no such element.
filter :: (a -> Bool) -> [a] -> [a] Source
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]
partition :: (a -> Bool) -> [a] -> ([a], [a]) Source
The partition
function takes a predicate a list and returns the pair of lists of elements which do and do not satisfy the predicate, respectively; i.e.,
partition p xs == (filter p xs, filter (not . p) xs)
These functions treat a list xs
as a indexed collection, with indices ranging from 0 to length xs - 1
.
(!!) :: [a] -> Int -> a infixl 9 Source
List index (subscript) operator, starting from 0. It is an instance of the more general genericIndex
, which takes an index of any integral type.
elemIndex :: Eq a => a -> [a] -> Maybe Int Source
The elemIndex
function returns the index of the first element in the given list which is equal (by ==
) to the query element, or Nothing
if there is no such element.
elemIndices :: Eq a => a -> [a] -> [Int] Source
The elemIndices
function extends elemIndex
, by returning the indices of all elements equal to the query element, in ascending order.
findIndex :: (a -> Bool) -> [a] -> Maybe Int Source
The findIndex
function takes a predicate and a list and returns the index of the first element in the list satisfying the predicate, or Nothing
if there is no such element.
findIndices :: (a -> Bool) -> [a] -> [Int] Source
The findIndices
function extends findIndex
, by returning the indices of all elements satisfying the predicate, in ascending order.
zip :: [a] -> [b] -> [(a, b)] Source
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.
zip
is right-lazy:
zip [] _|_ = []
zip3 :: [a] -> [b] -> [c] -> [(a, b, c)] Source
zip3
takes three lists and returns a list of triples, analogous to zip
.
zip4 :: [a] -> [b] -> [c] -> [d] -> [(a, b, c, d)] Source
The zip4
function takes four lists and returns a list of quadruples, analogous to zip
.
zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a, b, c, d, e)] Source
The zip5
function takes five lists and returns a list of five-tuples, analogous to zip
.
zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a, b, c, d, e, f)] Source
The zip6
function takes six lists and returns a list of six-tuples, analogous to zip
.
zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a, b, c, d, e, f, g)] Source
The zip7
function takes seven lists and returns a list of seven-tuples, analogous to zip
.
zipWith :: (a -> b -> c) -> [a] -> [b] -> [c] Source
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.
zipWith
is right-lazy:
zipWith f [] _|_ = []
zipWith3 :: (a -> b -> c -> d) -> [a] -> [b] -> [c] -> [d] Source
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
.
zipWith4 :: (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e] Source
The zipWith4
function takes a function which combines four elements, as well as four lists and returns a list of their point-wise combination, analogous to zipWith
.
zipWith5 :: (a -> b -> c -> d -> e -> f) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] Source
The zipWith5
function takes a function which combines five elements, as well as five lists and returns a list of their point-wise combination, analogous to zipWith
.
zipWith6 :: (a -> b -> c -> d -> e -> f -> g) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] Source
The zipWith6
function takes a function which combines six elements, as well as six lists and returns a list of their point-wise combination, analogous to zipWith
.
zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h] Source
The zipWith7
function takes a function which combines seven elements, as well as seven lists and returns a list of their point-wise combination, analogous to zipWith
.
unzip :: [(a, b)] -> ([a], [b]) Source
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]) Source
The unzip3
function takes a list of triples and returns three lists, analogous to unzip
.
unzip4 :: [(a, b, c, d)] -> ([a], [b], [c], [d]) Source
The unzip4
function takes a list of quadruples and returns four lists, analogous to unzip
.
unzip5 :: [(a, b, c, d, e)] -> ([a], [b], [c], [d], [e]) Source
The unzip5
function takes a list of five-tuples and returns five lists, analogous to unzip
.
unzip6 :: [(a, b, c, d, e, f)] -> ([a], [b], [c], [d], [e], [f]) Source
The unzip6
function takes a list of six-tuples and returns six lists, analogous to unzip
.
unzip7 :: [(a, b, c, d, e, f, g)] -> ([a], [b], [c], [d], [e], [f], [g]) Source
The unzip7
function takes a list of seven-tuples and returns seven lists, analogous to unzip
.
lines :: String -> [String] Source
lines
breaks a string up into a list of strings at newline characters. The resulting strings do not contain newlines.
Note that after splitting the string at newline characters, the last part of the string is considered a line even if it doesn't end with a newline. For example,
lines "" == [] lines "\n" == [""] lines "one" == ["one"] lines "one\n" == ["one"] lines "one\n\n" == ["one",""] lines "one\ntwo" == ["one","two"] lines "one\ntwo\n" == ["one","two"]
Thus lines s
contains at least as many elements as newlines in s
.
words :: String -> [String] Source
words
breaks a string up into a list of words, which were delimited by white space.
unlines :: [String] -> String Source
unlines
is an inverse operation to lines
. It joins lines, after appending a terminating newline to each.
unwords :: [String] -> String Source
unwords
is an inverse operation to words
. It joins words with separating spaces.
nub :: Eq a => [a] -> [a] Source
O(n^2). The nub
function removes duplicate elements from a list. In particular, it keeps only the first occurrence of each element. (The name nub
means `essence'.) It is a special case of nubBy
, which allows the programmer to supply their own equality test.
delete :: Eq a => a -> [a] -> [a] Source
delete
x
removes the first occurrence of x
from its list argument. For example,
delete 'a' "banana" == "bnana"
It is a special case of deleteBy
, which allows the programmer to supply their own equality test.
(\\) :: Eq a => [a] -> [a] -> [a] infix 5 Source
The \\
function is list difference (non-associative). In the result of xs
\\
ys
, the first occurrence of each element of ys
in turn (if any) has been removed from xs
. Thus
(xs ++ ys) \\ xs == ys.
It is a special case of deleteFirstsBy
, which allows the programmer to supply their own equality test.
union :: Eq a => [a] -> [a] -> [a] Source
The union
function returns the list union of the two lists. For example,
"dog" `union` "cow" == "dogcw"
Duplicates, and elements of the first list, are removed from the the second list, but if the first list contains duplicates, so will the result. It is a special case of unionBy
, which allows the programmer to supply their own equality test.
intersect :: Eq a => [a] -> [a] -> [a] Source
The intersect
function takes the list intersection of two lists. For example,
[1,2,3,4] `intersect` [2,4,6,8] == [2,4]
If the first list contains duplicates, so will the result.
[1,2,2,3,4] `intersect` [6,4,4,2] == [2,2,4]
It is a special case of intersectBy
, which allows the programmer to supply their own equality test. If the element is found in both the first and the second list, the element from the first list will be used.
sort :: Ord a => [a] -> [a] Source
The sort
function implements a stable sorting algorithm. It is a special case of sortBy
, which allows the programmer to supply their own comparison function.
Elements are arranged from from lowest to highest, keeping duplicates in the order they appeared in the input.
sortOn :: Ord b => (a -> b) -> [a] -> [a] Source
Sort a list by comparing the results of a key function applied to each element. sortOn f
is equivalent to sortBy (comparing f)
, but has the performance advantage of only evaluating f
once for each element in the input list. This is called the decorate-sort-undecorate paradigm, or Schwartzian transform.
Elements are arranged from from lowest to highest, keeping duplicates in the order they appeared in the input.
Since: 4.8.0.0
insert :: Ord a => a -> [a] -> [a] Source
The insert
function takes an element and a list and inserts the element into the list at the first position where it is less than or equal to the next element. In particular, if the list is sorted before the call, the result will also be sorted. It is a special case of insertBy
, which allows the programmer to supply their own comparison function.
By
" operationsBy convention, overloaded functions have a non-overloaded counterpart whose name is suffixed with `By
'.
It is often convenient to use these functions together with on
, for instance sortBy (compare
`on` fst)
.
Eq
context)The predicate is assumed to define an equivalence.
nubBy :: (a -> a -> Bool) -> [a] -> [a] Source
The nubBy
function behaves just like nub
, except it uses a user-supplied equality predicate instead of the overloaded ==
function.
deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a] Source
The deleteBy
function behaves like delete
, but takes a user-supplied equality predicate.
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] Source
The deleteFirstsBy
function takes a predicate and two lists and returns the first list with the first occurrence of each element of the second list removed.
unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] Source
The unionBy
function is the non-overloaded version of union
.
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] Source
The intersectBy
function is the non-overloaded version of intersect
.
groupBy :: (a -> a -> Bool) -> [a] -> [[a]] Source
The groupBy
function is the non-overloaded version of group
.
Ord
context)The function is assumed to define a total ordering.
sortBy :: (a -> a -> Ordering) -> [a] -> [a] Source
The sortBy
function is the non-overloaded version of sort
.
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a] Source
The non-overloaded version of insert
.
maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a Source
The largest element of a non-empty structure with respect to the given comparison function.
minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a Source
The least element of a non-empty structure with respect to the given comparison function.
generic
" operationsThe prefix `generic
' indicates an overloaded function that is a generalized version of a Prelude function.
genericLength :: Num i => [a] -> i Source
The genericLength
function is an overloaded version of length
. In particular, instead of returning an Int
, it returns any type which is an instance of Num
. It is, however, less efficient than length
.
genericTake :: Integral i => i -> [a] -> [a] Source
The genericTake
function is an overloaded version of take
, which accepts any Integral
value as the number of elements to take.
genericDrop :: Integral i => i -> [a] -> [a] Source
The genericDrop
function is an overloaded version of drop
, which accepts any Integral
value as the number of elements to drop.
genericSplitAt :: Integral i => i -> [a] -> ([a], [a]) Source
The genericSplitAt
function is an overloaded version of splitAt
, which accepts any Integral
value as the position at which to split.
genericIndex :: Integral i => [a] -> i -> a Source
The genericIndex
function is an overloaded version of !!
, which accepts any Integral
value as the index.
genericReplicate :: Integral i => i -> a -> [a] Source
The genericReplicate
function is an overloaded version of replicate
, which accepts any Integral
value as the number of repetitions to make.
© The University of Glasgow and others
Licensed under a BSD-style license (see top of the page).
https://downloads.haskell.org/~ghc/8.2.1/docs/html/libraries/base-4.10.0.0/Data-List.html