Commit ff844b6f authored by Andriy Palamarchuk's avatar Andriy Palamarchuk
Browse files

Added examples, more detailed documentation to Data.List Extracting sublists functions

parent 7ba42a34
......@@ -267,7 +267,12 @@ cycle [] = error "Prelude.cycle: empty list"
cycle xs = xs' where xs' = xs ++ xs'
-- | 'takeWhile', applied to a predicate @p@ and a list @xs@, returns the
-- longest prefix (possibly empty) of @xs@ of elements that satisfy @p@.
-- 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] == []
--
takeWhile :: (a -> Bool) -> [a] -> [a]
takeWhile _ [] = []
......@@ -275,7 +280,12 @@ takeWhile p (x:xs)
| p x = x : takeWhile p xs
| otherwise = []
-- | 'dropWhile' @p xs@ returns the suffix remaining after 'takeWhile' @p xs@.
-- | '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]
--
dropWhile :: (a -> Bool) -> [a] -> [a]
dropWhile _ [] = []
......@@ -284,19 +294,46 @@ dropWhile p xs@(x:xs')
| otherwise = xs
-- | 'take' @n@, applied to a list @xs@, returns the prefix of @xs@
-- of length @n@, or @xs@ itself if @n > 'length' 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 'Data.List.genericTake',
-- in which @n@ may be of any integral type.
take :: Int -> [a] -> [a]
-- | '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 'Data.List.genericDrop',
-- in which @n@ may be of any integral type.
drop :: Int -> [a] -> [a]
-- | 'splitAt' @n xs@ is equivalent to @('take' n xs, 'drop' n xs)@.
-- | '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)@.
-- 'splitAt' is an instance of the more general 'Data.List.genericSplitAt',
-- in which @n@ may be of any integral type.
splitAt :: Int -> [a] -> ([a],[a])
......@@ -381,7 +418,15 @@ splitAt (I# n#) ls
#endif /* USE_REPORT_PRELUDE */
-- | 'span' @p xs@ is equivalent to @('takeWhile' p xs, 'dropWhile' p xs)@
-- | '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)@
span :: (a -> Bool) -> [a] -> ([a],[a])
span _ xs@[] = (xs, xs)
......@@ -389,7 +434,15 @@ span p xs@(x:xs')
| p x = let (ys,zs) = span p xs' in (x:ys,zs)
| otherwise = ([],xs)
-- | 'break' @p@ is equivalent to @'span' ('not' . p)@.
-- | '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)@.
break :: (a -> Bool) -> [a] -> ([a],[a])
#ifdef USE_REPORT_PRELUDE
......
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