Safe Haskell | None |
---|---|
Language | Haskell98 |
Synopsis
- reduce :: ([a] -> a) -> [a] -> [a]
- trim :: String -> String
- rx :: String -> String -> Maybe String
- srx :: String -> String -> String -> String
- splitRx :: String -> String -> [String]
- lowerCase :: String -> String
- upperCase :: String -> String
- titleCase :: String -> String
- camelCase :: String -> String
- underscoreCase :: String -> String
- module Control.Lens
- module Data.Char
- (++) :: [a] -> [a] -> [a]
- filter :: (a -> Bool) -> [a] -> [a]
- zip :: [a] -> [b] -> [(a, b)]
- map :: (a -> b) -> [a] -> [b]
- product :: (Foldable t, Num a) => t a -> a
- sum :: (Foldable t, Num a) => t a -> a
- minimum :: (Foldable t, Ord a) => t a -> a
- maximum :: (Foldable t, Ord a) => t a -> a
- elem :: (Foldable t, Eq a) => a -> t a -> Bool
- length :: Foldable t => t a -> Int
- null :: Foldable t => t a -> Bool
- foldl1 :: Foldable t => (a -> a -> a) -> t a -> a
- foldr1 :: Foldable t => (a -> a -> a) -> t a -> a
- foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b
- foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b
- foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b
- head :: [a] -> a
- tail :: [a] -> [a]
- last :: [a] -> a
- init :: [a] -> [a]
- scanl :: (b -> a -> b) -> b -> [a] -> [b]
- scanl1 :: (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]
- takeWhile :: (a -> Bool) -> [a] -> [a]
- dropWhile :: (a -> Bool) -> [a] -> [a]
- take :: Int -> [a] -> [a]
- drop :: Int -> [a] -> [a]
- splitAt :: Int -> [a] -> ([a], [a])
- span :: (a -> Bool) -> [a] -> ([a], [a])
- break :: (a -> Bool) -> [a] -> ([a], [a])
- reverse :: [a] -> [a]
- lookup :: Eq a => a -> [(a, b)] -> Maybe b
- (!!) :: [a] -> Int -> a
- 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])
- isPrefixOf :: Eq a => [a] -> [a] -> Bool
- isSuffixOf :: Eq a => [a] -> [a] -> Bool
- isInfixOf :: Eq a => [a] -> [a] -> Bool
- nub :: Eq a => [a] -> [a]
- nubBy :: (a -> a -> Bool) -> [a] -> [a]
- intersperse :: a -> [a] -> [a]
- intercalate :: [a] -> [[a]] -> [a]
- sort :: Ord a => [a] -> [a]
- sortBy :: (a -> a -> Ordering) -> [a] -> [a]
- unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
- lines :: String -> [String]
- unlines :: [String] -> String
- words :: String -> [String]
- unwords :: [String] -> String
- concat :: Foldable t => t [a] -> [a]
- concatMap :: Foldable t => (a -> [b]) -> t a -> [b]
- and :: Foldable t => t Bool -> Bool
- or :: Foldable t => t Bool -> Bool
- any :: Foldable t => (a -> Bool) -> t a -> Bool
- all :: Foldable t => (a -> Bool) -> t a -> Bool
- notElem :: (Foldable t, Eq a) => a -> t a -> Bool
- find :: Foldable t => (a -> Bool) -> t a -> Maybe a
- isSubsequenceOf :: Eq a => [a] -> [a] -> Bool
- mapAccumR :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c)
- mapAccumL :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c)
- minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a
- sortOn :: Ord b => (a -> b) -> [a] -> [a]
- permutations :: [a] -> [[a]]
- subsequences :: [a] -> [[a]]
- tails :: [a] -> [[a]]
- inits :: [a] -> [[a]]
- groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
- group :: Eq a => [a] -> [[a]]
- deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- unzip7 :: [(a, b, c, d, e, f, g)] -> ([a], [b], [c], [d], [e], [f], [g])
- unzip6 :: [(a, b, c, d, e, f)] -> ([a], [b], [c], [d], [e], [f])
- unzip5 :: [(a, b, c, d, e)] -> ([a], [b], [c], [d], [e])
- unzip4 :: [(a, b, c, d)] -> ([a], [b], [c], [d])
- zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h]
- zipWith6 :: (a -> b -> c -> d -> e -> f -> g) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g]
- zipWith5 :: (a -> b -> c -> d -> e -> f) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f]
- zipWith4 :: (a -> b -> c -> d -> e) -> [a] -> [b] -> [c] -> [d] -> [e]
- zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [(a, b, c, d, e, f, g)]
- zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [(a, b, c, d, e, f)]
- zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a, b, c, d, e)]
- zip4 :: [a] -> [b] -> [c] -> [d] -> [(a, b, c, d)]
- genericReplicate :: Integral i => i -> a -> [a]
- genericIndex :: Integral i => [a] -> i -> a
- genericSplitAt :: Integral i => i -> [a] -> ([a], [a])
- genericDrop :: Integral i => i -> [a] -> [a]
- genericTake :: Integral i => i -> [a] -> [a]
- genericLength :: Num i => [a] -> i
- insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]
- insert :: Ord a => a -> [a] -> [a]
- partition :: (a -> Bool) -> [a] -> ([a], [a])
- transpose :: [[a]] -> [[a]]
- intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- intersect :: Eq a => [a] -> [a] -> [a]
- unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
- union :: Eq a => [a] -> [a] -> [a]
- (\\) :: Eq a => [a] -> [a] -> [a]
- deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
- delete :: Eq a => a -> [a] -> [a]
- findIndices :: (a -> Bool) -> [a] -> [Int]
- findIndex :: (a -> Bool) -> [a] -> Maybe Int
- elemIndices :: Eq a => a -> [a] -> [Int]
- elemIndex :: Eq a => a -> [a] -> Maybe Int
- stripPrefix :: Eq a => [a] -> [a] -> Maybe [a]
- dropWhileEnd :: (a -> Bool) -> [a] -> [a]
- iterate' :: (a -> a) -> a -> [a]
- scanl' :: (b -> a -> b) -> b -> [a] -> [b]
- foldl1' :: (a -> a -> a) -> [a] -> a
- module Data.Maybe
Documentation
Regexes
Case
underscoreCase :: String -> String Source #
Convert to underscore case
module Control.Lens
module Data.Char
(++) :: [a] -> [a] -> [a] infixr 5 #
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]
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, ...]
product :: (Foldable t, Num a) => t a -> a #
The product
function computes the product of the numbers of a
structure.
sum :: (Foldable t, Num a) => t a -> a #
The sum
function computes the sum of the numbers of a structure.
length :: Foldable t => t a -> Int #
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.
null :: Foldable t => t a -> Bool #
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.
foldl' :: Foldable t => (b -> a -> b) -> b -> t a -> b #
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
foldl :: Foldable t => (b -> a -> b) -> b -> t a -> b #
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
in the above example)
before applying them to the operator (e.g. to f
x1(
). This results
in a thunk chain f
x2)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
foldr :: Foldable t => (a -> b -> b) -> b -> t a -> b #
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
Return all the elements of a list except the last one. The list must be non-empty.
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
ties a finite list into a circular one, or equivalently,
the infinite repetition of the original list. It is the identity
on infinite lists.
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
:
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] == []
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
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]) #
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 (
when take
n xs, drop
n xs)n
is not _|_
(splitAt _|_ xs = _|_
).
splitAt
is an instance of the more general genericSplitAt
,
in which n
may be of any integral type.
span :: (a -> Bool) -> [a] -> ([a], [a]) #
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])
break :: (a -> Bool) -> [a] -> ([a], [a]) #
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],[])
lookup :: Eq a => a -> [(a, b)] -> Maybe b #
lookup
key assocs
looks up a key in an association list.
(!!) :: [a] -> Int -> a infixl 9 #
List index (subscript) operator, starting from 0.
It is an instance of the more general genericIndex
,
which takes an index of any integral type.
unzip :: [(a, b)] -> ([a], [b]) #
unzip
transforms a list of pairs into a list of first components
and a list of second components.
isPrefixOf :: Eq a => [a] -> [a] -> Bool #
The isPrefixOf
function takes two lists and returns True
iff the first list is a prefix of the second.
>>>
"Hello" `isPrefixOf` "Hello World!"
True
>>>
"Hello" `isPrefixOf` "Wello Horld!"
False
isSuffixOf :: Eq a => [a] -> [a] -> Bool #
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.
>>>
"ld!" `isSuffixOf` "Hello World!"
True
>>>
"World" `isSuffixOf` "Hello World!"
False
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.
>>>
nub [1,2,3,4,3,2,1,2,4,3,5]
[1,2,3,4,5]
intersperse :: a -> [a] -> [a] #
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] #
intercalate
xs xss
is equivalent to (
.
It inserts the list concat
(intersperse
xs xss))xs
in between the lists in xss
and concatenates the
result.
>>>
intercalate ", " ["Lorem", "ipsum", "dolor"]
"Lorem, ipsum, dolor"
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.
>>>
sort [1,6,4,3,2,5]
[1,2,3,4,5,6]
unfoldr :: (b -> Maybe (a, b)) -> b -> [a] #
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]
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
contains at least as many elements as newlines in lines
ss
.
words
breaks a string up into a list of words, which were delimited
by white space.
>>>
words "Lorem ipsum\ndolor"
["Lorem","ipsum","dolor"]
concat :: Foldable t => t [a] -> [a] #
The concatenation of all the elements of a container of lists.
concatMap :: Foldable t => (a -> [b]) -> t a -> [b] #
Map a function over all the elements of a container and concatenate the resulting lists.
any :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether any element of the structure satisfies the predicate.
all :: Foldable t => (a -> Bool) -> t a -> Bool #
Determines whether all elements of the structure satisfy the predicate.
isSubsequenceOf :: Eq a => [a] -> [a] -> Bool #
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.
is equivalent to isSubsequenceOf
x y
.elem
x (subsequences
y)
Examples
>>>
isSubsequenceOf "GHC" "The Glorious Haskell Compiler"
True>>>
isSubsequenceOf ['a','d'..'z'] ['a'..'z']
True>>>
isSubsequenceOf [1..10] [10,9..0]
False
Since: base-4.8.0.0
mapAccumR :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) #
mapAccumL :: Traversable t => (a -> b -> (a, c)) -> a -> t b -> (a, t c) #
minimumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #
The least element of a non-empty structure with respect to the given comparison function.
maximumBy :: Foldable t => (a -> a -> Ordering) -> t a -> a #
The largest element of a non-empty structure with respect to the given comparison function.
sortOn :: Ord b => (a -> b) -> [a] -> [a] #
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.
>>>
sortOn fst [(2, "world"), (4, "!"), (1, "Hello")]
[(1,"Hello"),(2,"world"),(4,"!")]
Since: base-4.8.0.0
permutations :: [a] -> [[a]] #
The permutations
function returns the list of all permutations of the argument.
>>>
permutations "abc"
["abc","bac","cba","bca","cab","acb"]
subsequences :: [a] -> [[a]] #
The subsequences
function returns the list of all subsequences of the argument.
>>>
subsequences "abc"
["","a","b","ab","c","ac","bc","abc"]
group :: Eq a => [a] -> [[a]] #
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.
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #
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.
zipWith7 :: (a -> b -> c -> d -> e -> f -> g -> h) -> [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g] -> [h] #
genericReplicate :: Integral i => i -> a -> [a] #
The genericReplicate
function is an overloaded version of replicate
,
which accepts any Integral
value as the number of repetitions to make.
genericIndex :: Integral i => [a] -> i -> a #
The genericIndex
function is an overloaded version of !!
, which
accepts any Integral
value as the index.
genericSplitAt :: Integral i => i -> [a] -> ([a], [a]) #
The genericSplitAt
function is an overloaded version of splitAt
, which
accepts any Integral
value as the position at which to split.
genericDrop :: Integral i => i -> [a] -> [a] #
The genericDrop
function is an overloaded version of drop
, which
accepts any Integral
value as the number of elements to drop.
genericTake :: Integral i => i -> [a] -> [a] #
The genericTake
function is an overloaded version of take
, which
accepts any Integral
value as the number of elements to take.
genericLength :: Num i => [a] -> i #
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
.
insert :: Ord a => a -> [a] -> [a] #
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.
>>>
insert 4 [1,2,3,5,6,7]
[1,2,3,4,5,6,7]
partition :: (a -> Bool) -> [a] -> ([a], [a]) #
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)
>>>
partition (`elem` "aeiou") "Hello World!"
("eoo","Hll Wrld!")
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]]
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] #
The intersectBy
function is the non-overloaded version of intersect
.
intersect :: Eq a => [a] -> [a] -> [a] #
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.
union :: Eq a => [a] -> [a] -> [a] #
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.
(\\) :: Eq a => [a] -> [a] -> [a] infix 5 #
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.
>>>
"Hello World!" \\ "ell W"
"Hoorld!"
It is a special case of deleteFirstsBy
, which allows the programmer
to supply their own equality test.
findIndices :: (a -> Bool) -> [a] -> [Int] #
The findIndices
function extends findIndex
, by returning the
indices of all elements satisfying the predicate, in ascending order.
>>>
findIndices (`elem` "aeiou") "Hello World!"
[1,4,7]
elemIndices :: Eq a => a -> [a] -> [Int] #
The elemIndices
function extends elemIndex
, by returning the
indices of all elements equal to the query element, in ascending order.
>>>
elemIndices 'o' "Hello World"
[4,7]
stripPrefix :: Eq a => [a] -> [a] -> Maybe [a] #
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
dropWhileEnd :: (a -> Bool) -> [a] -> [a] #
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: base-4.5.0.0
iterate' :: (a -> a) -> a -> [a] #
'iterate\'' is the strict version of iterate
.
It ensures that the result of each application of force to weak head normal form before proceeding.
module Data.Maybe