module Data.List
(
- [] (..),
-
- , elemIndex -- :: (Eq a) => a -> [a] -> Maybe Int
- , elemIndices -- :: (Eq a) => a -> [a] -> [Int]
-
- , find -- :: (a -> Bool) -> [a] -> Maybe a
- , findIndex -- :: (a -> Bool) -> [a] -> Maybe Int
- , findIndices -- :: (a -> Bool) -> [a] -> [Int]
-
- , nub -- :: (Eq a) => [a] -> [a]
- , nubBy -- :: (a -> a -> Bool) -> [a] -> [a]
-
- , delete -- :: (Eq a) => a -> [a] -> [a]
- , deleteBy -- :: (a -> a -> Bool) -> a -> [a] -> [a]
- , (\\) -- :: (Eq a) => [a] -> [a] -> [a]
- , deleteFirstsBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
-
- , union -- :: (Eq a) => [a] -> [a] -> [a]
- , unionBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
-
- , intersect -- :: (Eq a) => [a] -> [a] -> [a]
- , intersectBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
-
- , intersperse -- :: a -> [a] -> [a]
- , transpose -- :: [[a]] -> [[a]]
- , partition -- :: (a -> Bool) -> [a] -> ([a], [a])
-
- , group -- :: Eq a => [a] -> [[a]]
- , groupBy -- :: (a -> a -> Bool) -> [a] -> [[a]]
-
- , inits -- :: [a] -> [[a]]
- , tails -- :: [a] -> [[a]]
-
- , isPrefixOf -- :: (Eq a) => [a] -> [a] -> Bool
- , isSuffixOf -- :: (Eq a) => [a] -> [a] -> Bool
-
- , mapAccumL -- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c])
- , mapAccumR -- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c])
-
- , sort -- :: (Ord a) => [a] -> [a]
- , sortBy -- :: (a -> a -> Ordering) -> [a] -> [a]
-
- , insert -- :: (Ord a) => a -> [a] -> [a]
- , insertBy -- :: (a -> a -> Ordering) -> a -> [a] -> [a]
-
- , maximumBy -- :: (a -> a -> Ordering) -> [a] -> a
- , minimumBy -- :: (a -> a -> Ordering) -> [a] -> a
-
- , genericLength -- :: (Integral a) => [b] -> a
- , genericTake -- :: (Integral a) => a -> [b] -> [b]
- , genericDrop -- :: (Integral a) => a -> [b] -> [b]
- , genericSplitAt -- :: (Integral a) => a -> [b] -> ([b], [b])
- , genericIndex -- :: (Integral a) => [b] -> a -> b
- , genericReplicate -- :: (Integral a) => a -> b -> [b]
-
- , unfoldr -- :: (b -> Maybe (a, b)) -> b -> [a]
+#ifdef __NHC__
+ [] (..)
+ ,
+#endif
- , zip4, zip5, zip6, zip7
- , zipWith4, zipWith5, zipWith6, zipWith7
- , unzip4, unzip5, unzip6, unzip7
+ -- * Basic functions
- , map -- :: ( a -> b ) -> [a] -> [b]
- , (++) -- :: [a] -> [a] -> [a]
- , concat -- :: [[a]] -> [a]
- , filter -- :: (a -> Bool) -> [a] -> [a]
+ (++) -- :: [a] -> [a] -> [a]
, head -- :: [a] -> a
, last -- :: [a] -> a
, tail -- :: [a] -> [a]
, init -- :: [a] -> [a]
, null -- :: [a] -> Bool
, length -- :: [a] -> Int
- , (!!) -- :: [a] -> Int -> a
+
+ -- * List transformations
+ , map -- :: (a -> b) -> [a] -> [b]
+ , reverse -- :: [a] -> [a]
+
+ , intersperse -- :: a -> [a] -> [a]
+ , transpose -- :: [[a]] -> [[a]]
+
+ -- * Reducing lists (folds)
+
, foldl -- :: (a -> b -> a) -> a -> [b] -> 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
+
+ -- ** Special folds
+
+ , concat -- :: [[a]] -> [a]
+ , concatMap -- :: (a -> [b]) -> [a] -> [b]
+ , and -- :: [Bool] -> Bool
+ , or -- :: [Bool] -> Bool
+ , any -- :: (a -> Bool) -> [a] -> Bool
+ , all -- :: (a -> Bool) -> [a] -> Bool
+ , sum -- :: (Num a) => [a] -> a
+ , product -- :: (Num a) => [a] -> a
+ , maximum -- :: (Ord a) => [a] -> a
+ , minimum -- :: (Ord a) => [a] -> a
+
+ -- * Building lists
+
+ -- ** Scans
+ , scanl -- :: (a -> b -> a) -> a -> [b] -> [a]
+ , scanl1 -- :: (a -> a -> a) -> [a] -> [a]
, scanr -- :: (a -> b -> b) -> b -> [a] -> [b]
, scanr1 -- :: (a -> a -> a) -> [a] -> [a]
+
+ -- ** Accumulating maps
+ , mapAccumL -- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c])
+ , mapAccumR -- :: (a -> b -> (a,c)) -> a -> [b] -> (a,[c])
+
+ -- ** Infinite lists
, iterate -- :: (a -> a) -> a -> [a]
, repeat -- :: a -> [a]
, replicate -- :: Int -> a -> [a]
, cycle -- :: [a] -> [a]
+
+ -- ** Unfolding
+ , unfoldr -- :: (b -> Maybe (a, b)) -> b -> [a]
+
+ -- * Sublists
+
+ -- ** Extracting sublists
, 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])
- , lines -- :: String -> [String]
- , words -- :: String -> [String]
- , unlines -- :: [String] -> String
- , unwords -- :: [String] -> String
- , reverse -- :: [a] -> [a]
- , and -- :: [Bool] -> Bool
- , or -- :: [Bool] -> Bool
- , any -- :: (a -> Bool) -> [a] -> Bool
- , all -- :: (a -> Bool) -> [a] -> Bool
+ , group -- :: Eq a => [a] -> [[a]]
+
+ , inits -- :: [a] -> [[a]]
+ , tails -- :: [a] -> [[a]]
+
+ -- ** Predicates
+ , isPrefixOf -- :: (Eq a) => [a] -> [a] -> Bool
+ , isSuffixOf -- :: (Eq a) => [a] -> [a] -> Bool
+
+ -- * Searching lists
+
+ -- ** Searching by equality
, elem -- :: a -> [a] -> Bool
, notElem -- :: a -> [a] -> Bool
, lookup -- :: (Eq a) => a -> [(a,b)] -> Maybe b
- , sum -- :: (Num a) => [a] -> a
- , product -- :: (Num a) => [a] -> a
- , maximum -- :: (Ord a) => [a] -> a
- , minimum -- :: (Ord a) => [a] -> a
- , concatMap -- :: (a -> [b]) -> [a] -> [b]
+
+ -- ** Searching with a predicate
+ , find -- :: (a -> Bool) -> [a] -> Maybe a
+ , filter -- :: (a -> Bool) -> [a] -> [a]
+ , partition -- :: (a -> Bool) -> [a] -> ([a], [a])
+
+ -- * Indexing lists
+ -- | These functions treat a list @xs@ as a indexed collection,
+ -- with indices ranging from 0 to @'length' xs - 1@.
+
+ , (!!) -- :: [a] -> Int -> a
+
+ , elemIndex -- :: (Eq a) => a -> [a] -> Maybe Int
+ , elemIndices -- :: (Eq a) => a -> [a] -> [Int]
+
+ , findIndex -- :: (a -> Bool) -> [a] -> Maybe Int
+ , findIndices -- :: (a -> Bool) -> [a] -> [Int]
+
+ -- * Zipping and unzipping lists
+
, zip -- :: [a] -> [b] -> [(a,b)]
, zip3
+ , zip4, zip5, zip6, zip7
+
, zipWith -- :: (a -> b -> c) -> [a] -> [b] -> [c]
, zipWith3
+ , zipWith4, zipWith5, zipWith6, zipWith7
+
, unzip -- :: [(a,b)] -> ([a],[b])
, unzip3
+ , unzip4, unzip5, unzip6, unzip7
+
+ -- * Special lists
+
+ -- ** Functions on strings
+ , lines -- :: String -> [String]
+ , words -- :: String -> [String]
+ , unlines -- :: [String] -> String
+ , unwords -- :: [String] -> String
+
+ -- ** \"Set\" operations
+
+ , nub -- :: (Eq a) => [a] -> [a]
+
+ , delete -- :: (Eq a) => a -> [a] -> [a]
+ , (\\) -- :: (Eq a) => [a] -> [a] -> [a]
+
+ , union -- :: (Eq a) => [a] -> [a] -> [a]
+ , intersect -- :: (Eq a) => [a] -> [a] -> [a]
+
+ -- ** Ordered lists
+ , sort -- :: (Ord a) => [a] -> [a]
+ , insert -- :: (Ord a) => a -> [a] -> [a]
+
+ -- * Generalized functions
+
+ -- ** The \"@By@\" operations
+ -- | By convention, overloaded functions have a non-overloaded
+ -- counterpart whose name is suffixed with \`@By@\'.
+
+ -- *** User-supplied equality (replacing an @Eq@ context)
+ -- | The predicate is assumed to define an equivalence.
+ , nubBy -- :: (a -> a -> Bool) -> [a] -> [a]
+ , deleteBy -- :: (a -> a -> Bool) -> a -> [a] -> [a]
+ , deleteFirstsBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
+ , unionBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
+ , intersectBy -- :: (a -> a -> Bool) -> [a] -> [a] -> [a]
+ , groupBy -- :: (a -> a -> Bool) -> [a] -> [[a]]
+
+ -- *** User-supplied comparison (replacing an @Ord@ context)
+ -- | The function is assumed to define a total ordering.
+ , sortBy -- :: (a -> a -> Ordering) -> [a] -> [a]
+ , insertBy -- :: (a -> a -> Ordering) -> a -> [a] -> [a]
+ , maximumBy -- :: (a -> a -> Ordering) -> [a] -> a
+ , minimumBy -- :: (a -> a -> Ordering) -> [a] -> a
+
+ -- ** The \"@generic@\" operations
+ -- | The prefix \`@generic@\' indicates an overloaded function that
+ -- is a generalized version of a "Prelude" function.
+
+ , genericLength -- :: (Integral a) => [b] -> a
+ , genericTake -- :: (Integral a) => a -> [b] -> [b]
+ , genericDrop -- :: (Integral a) => a -> [b] -> [b]
+ , genericSplitAt -- :: (Integral a) => a -> [b] -> ([b], [b])
+ , genericIndex -- :: (Integral a) => [b] -> a -> b
+ , genericReplicate -- :: (Integral a) => a -> b -> [b]
) where
+#ifdef __NHC__
+import Prelude hiding (Maybe(..))
+#endif
+
import Data.Maybe
+import Data.Char ( isSpace )
#ifdef __GLASGOW_HASKELL__
import GHC.Num
import GHC.Real
import GHC.List
-import GHC.Show ( lines, words, unlines, unwords )
import GHC.Base
#endif
-- -----------------------------------------------------------------------------
-- List functions
+-- | 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.
elemIndex :: Eq a => a -> [a] -> Maybe Int
elemIndex x = findIndex (x==)
+-- | The 'elemIndices' function extends 'elemIndex', by returning the
+-- indices of all elements equal to the query element, in ascending order.
elemIndices :: Eq a => a -> [a] -> [Int]
elemIndices x = findIndices (x==)
+-- | The 'find' function takes a predicate and a list and returns the
+-- first element in the list matching the predicate, or 'Nothing' if
+-- there is no such element.
find :: (a -> Bool) -> [a] -> Maybe a
find p = listToMaybe . filter p
+-- | 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.
findIndex :: (a -> Bool) -> [a] -> Maybe Int
findIndex p = listToMaybe . findIndices p
+-- | The 'findIndices' function extends 'findIndex', by returning the
+-- indices of all elements satisfying the predicate, in ascending order.
findIndices :: (a -> Bool) -> [a] -> [Int]
-#ifdef USE_REPORT_PRELUDE
+#if defined(USE_REPORT_PRELUDE) || !defined(__GLASGOW_HASKELL__)
findIndices p xs = [ i | (x,i) <- zip xs [0..], p x]
#else
-#ifdef __HUGS__
-findIndices p xs = [ i | (x,i) <- zip xs [0..], p x]
-#else
-- Efficient definition
findIndices p ls = loop 0# ls
where
loop _ [] = []
loop n (x:xs) | p x = I# n : loop (n +# 1#) xs
| otherwise = loop (n +# 1#) xs
-#endif /* __HUGS__ */
#endif /* USE_REPORT_PRELUDE */
+-- | The 'isPrefixOf' function takes two lists and returns 'True'
+-- iff the first list is a prefix of the second.
isPrefixOf :: (Eq a) => [a] -> [a] -> Bool
isPrefixOf [] _ = True
isPrefixOf _ [] = False
isPrefixOf (x:xs) (y:ys)= x == y && isPrefixOf xs ys
+-- | The 'isSuffixOf' function takes two lists and returns 'True'
+-- iff the first list is a suffix of the second.
+-- Both lists must be finite.
isSuffixOf :: (Eq a) => [a] -> [a] -> Bool
isSuffixOf x y = reverse x `isPrefixOf` reverse y
--- nub (meaning "essence") remove duplicate elements from its list argument.
+-- | 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 :: (Eq a) => [a] -> [a]
#ifdef USE_REPORT_PRELUDE
nub = nubBy (==)
| otherwise = x : nub' xs (x:ls) -- '
#endif
+-- | The 'nubBy' function behaves just like 'nub', except it uses a
+-- user-supplied equality predicate instead of the overloaded '=='
+-- function.
nubBy :: (a -> a -> Bool) -> [a] -> [a]
#ifdef USE_REPORT_PRELUDE
nubBy eq [] = []
#endif
--- delete x removes the first occurrence of x from its list argument.
+-- | '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.
+
delete :: (Eq a) => a -> [a] -> [a]
delete = deleteBy (==)
+-- | The 'deleteBy' function behaves like 'delete', but takes a
+-- user-supplied equality predicate.
deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]
deleteBy _ _ [] = []
deleteBy eq x (y:ys) = if x `eq` y then ys else y : deleteBy eq x ys
--- 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.
+-- | 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.
+
(\\) :: (Eq a) => [a] -> [a] -> [a]
(\\) = foldl (flip delete)
--- List union, remove the elements of first list from second.
+-- | 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.
+
union :: (Eq a) => [a] -> [a] -> [a]
union = unionBy (==)
+-- | The 'unionBy' function is the non-overloaded version of 'union'.
unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
unionBy eq xs ys = xs ++ foldl (flip (deleteBy eq)) (nubBy eq ys) xs
+-- | 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.
+-- It is a special case of 'intersectBy', which allows the programmer to
+-- supply their own equality test.
+
intersect :: (Eq a) => [a] -> [a] -> [a]
intersect = intersectBy (==)
+-- | The 'intersectBy' function is the non-overloaded version of 'intersect'.
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
intersectBy eq xs ys = [x | x <- xs, any (eq x) ys]
--- intersperse sep inserts sep between the elements of its list argument.
--- e.g. intersperse ',' "abcde" == "a,b,c,d,e"
+-- | 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"
+
intersperse :: a -> [a] -> [a]
intersperse _ [] = []
intersperse _ [x] = [x]
intersperse sep (x:xs) = x : sep : intersperse sep xs
+-- | 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]]
+
transpose :: [[a]] -> [[a]]
transpose [] = []
transpose ([] : xss) = transpose xss
transpose ((x:xs) : xss) = (x : [h | (h:t) <- xss]) : transpose (xs : [ t | (h:t) <- xss])
--- partition takes a predicate and a list and returns a pair of lists:
--- those elements of the argument list that do and do not satisfy the
--- predicate, respectively; i,e,,
--- partition p xs == (filter p xs, filter (not . p) xs).
+-- | 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 :: (a -> Bool) -> [a] -> ([a],[a])
{-# INLINE partition #-}
partition p xs = foldr (select p) ([],[]) xs
select p x (ts,fs) | p x = (x:ts,fs)
| otherwise = (ts, x:fs)
--- @mapAccumL@ behaves like a combination
--- of @map@ and @foldl@;
--- it applies a function to each element of a list, passing an accumulating
--- parameter from left to right, and returning a final value of this
--- accumulator together with the new list.
-
+-- | The 'mapAccumL' function behaves like a combination of 'map' and
+-- 'foldl'; it applies a function to each element of a list, passing
+-- an accumulating parameter from left to right, and returning a final
+-- value of this accumulator together with the new list.
mapAccumL :: (acc -> x -> (acc, y)) -- Function of elt of input list
-- and accumulator, returning new
-- accumulator and elt of result list
where (s', y ) = f s x
(s'',ys) = mapAccumL f s' xs
--- @mapAccumR@ does the same, but working from right to left instead.
--- Its type is the same as @mapAccumL@, though.
-
+-- | The 'mapAccumR' function behaves like a combination of 'map' and
+-- 'foldr'; it applies a function to each element of a list, passing
+-- an accumulating parameter from right to left, and returning a final
+-- value of this accumulator together with the new list.
mapAccumR :: (acc -> x -> (acc, y)) -- Function of elt of input list
-- and accumulator, returning new
-- accumulator and elt of result list
where (s'',y ) = f s' x
(s', ys) = mapAccumR f s xs
-
+-- | The 'insert' function takes an element and a list and inserts the
+-- element into the list at the last position where it is still 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 :: Ord a => a -> [a] -> [a]
insert e ls = insertBy (compare) e ls
+-- | The non-overloaded version of 'insert'.
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]
insertBy _ x [] = [x]
insertBy cmp x ys@(y:ys')
GT -> y : insertBy cmp x ys'
_ -> x : ys
+-- | The 'maximumBy' function takes a comparison function and a list
+-- and returns the greatest element of the list by the comparison function.
+-- The list must be finite and non-empty.
maximumBy :: (a -> a -> Ordering) -> [a] -> a
maximumBy _ [] = error "List.maximumBy: empty list"
maximumBy cmp xs = foldl1 max xs
GT -> x
_ -> y
+-- | The 'minimumBy' function takes a comparison function and a list
+-- and returns the least element of the list by the comparison function.
+-- The list must be finite and non-empty.
minimumBy :: (a -> a -> Ordering) -> [a] -> a
minimumBy _ [] = error "List.minimumBy: empty list"
minimumBy cmp xs = foldl1 min xs
GT -> y
_ -> x
+-- | 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'.
genericLength :: (Num i) => [b] -> i
genericLength [] = 0
genericLength (_:l) = 1 + genericLength l
+-- | The 'genericTake' function is an overloaded version of 'take', which
+-- accepts any 'Integral' value as the number of elements to take.
genericTake :: (Integral i) => i -> [a] -> [a]
genericTake 0 _ = []
genericTake _ [] = []
genericTake n (x:xs) | n > 0 = x : genericTake (n-1) xs
genericTake _ _ = error "List.genericTake: negative argument"
+-- | The 'genericDrop' function is an overloaded version of 'drop', which
+-- accepts any 'Integral' value as the number of elements to drop.
genericDrop :: (Integral i) => i -> [a] -> [a]
genericDrop 0 xs = xs
genericDrop _ [] = []
genericDrop n (_:xs) | n > 0 = genericDrop (n-1) xs
genericDrop _ _ = error "List.genericDrop: negative argument"
+-- | The 'genericSplitAt' function is an overloaded version of 'splitAt', which
+-- accepts any 'Integral' value as the position at which to split.
genericSplitAt :: (Integral i) => i -> [b] -> ([b],[b])
genericSplitAt 0 xs = ([],xs)
genericSplitAt _ [] = ([],[])
(xs',xs'') = genericSplitAt (n-1) xs
genericSplitAt _ _ = error "List.genericSplitAt: negative argument"
-
+-- | The 'genericIndex' function is an overloaded version of '!!', which
+-- accepts any 'Integral' value as the index.
genericIndex :: (Integral a) => [b] -> a -> b
genericIndex (x:_) 0 = x
genericIndex (_:xs) n
| otherwise = error "List.genericIndex: negative argument."
genericIndex _ _ = error "List.genericIndex: index too large."
+-- | The 'genericReplicate' function is an overloaded version of 'replicate',
+-- which accepts any 'Integral' value as the number of repetitions to make.
genericReplicate :: (Integral i) => i -> a -> [a]
genericReplicate n x = genericTake n (repeat x)
-
+-- | The 'zip4' function takes four lists and returns a list of
+-- quadruples, analogous to 'zip'.
zip4 :: [a] -> [b] -> [c] -> [d] -> [(a,b,c,d)]
zip4 = zipWith4 (,,,)
+-- | The 'zip5' function takes five lists and returns a list of
+-- five-tuples, analogous to 'zip'.
zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a,b,c,d,e)]
zip5 = zipWith5 (,,,,)
+-- | The 'zip6' function takes six lists and returns a list of six-tuples,
+-- analogous to 'zip'.
zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] ->
[(a,b,c,d,e,f)]
zip6 = zipWith6 (,,,,,)
+-- | The 'zip7' function takes seven lists and returns a list of
+-- seven-tuples, analogous to 'zip'.
zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] ->
[g] -> [(a,b,c,d,e,f,g)]
zip7 = zipWith7 (,,,,,,)
+-- | 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'.
zipWith4 :: (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]
zipWith4 z (a:as) (b:bs) (c:cs) (d:ds)
= z a b c d : zipWith4 z as bs cs ds
zipWith4 _ _ _ _ _ = []
+-- | 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'.
zipWith5 :: (a->b->c->d->e->f) ->
[a]->[b]->[c]->[d]->[e]->[f]
zipWith5 z (a:as) (b:bs) (c:cs) (d:ds) (e:es)
= z a b c d e : zipWith5 z as bs cs ds es
zipWith5 _ _ _ _ _ _ = []
+-- | 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'.
zipWith6 :: (a->b->c->d->e->f->g) ->
[a]->[b]->[c]->[d]->[e]->[f]->[g]
zipWith6 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs)
= z a b c d e f : zipWith6 z as bs cs ds es fs
zipWith6 _ _ _ _ _ _ _ = []
+-- | 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'.
zipWith7 :: (a->b->c->d->e->f->g->h) ->
[a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]
zipWith7 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs) (g:gs)
= z a b c d e f g : zipWith7 z as bs cs ds es fs gs
zipWith7 _ _ _ _ _ _ _ _ = []
+-- | The 'unzip4' function takes a list of quadruples and returns four
+-- lists, analogous to 'unzip'.
unzip4 :: [(a,b,c,d)] -> ([a],[b],[c],[d])
unzip4 = foldr (\(a,b,c,d) ~(as,bs,cs,ds) ->
(a:as,b:bs,c:cs,d:ds))
([],[],[],[])
+-- | The 'unzip5' function takes a list of five-tuples and returns five
+-- lists, analogous to 'unzip'.
unzip5 :: [(a,b,c,d,e)] -> ([a],[b],[c],[d],[e])
unzip5 = foldr (\(a,b,c,d,e) ~(as,bs,cs,ds,es) ->
(a:as,b:bs,c:cs,d:ds,e:es))
([],[],[],[],[])
+-- | The 'unzip6' function takes a list of six-tuples and returns six
+-- lists, analogous to 'unzip'.
unzip6 :: [(a,b,c,d,e,f)] -> ([a],[b],[c],[d],[e],[f])
unzip6 = foldr (\(a,b,c,d,e,f) ~(as,bs,cs,ds,es,fs) ->
(a:as,b:bs,c:cs,d:ds,e:es,f:fs))
([],[],[],[],[],[])
+-- | The 'unzip7' function takes a list of seven-tuples and returns
+-- seven lists, analogous to 'unzip'.
unzip7 :: [(a,b,c,d,e,f,g)] -> ([a],[b],[c],[d],[e],[f],[g])
unzip7 = foldr (\(a,b,c,d,e,f,g) ~(as,bs,cs,ds,es,fs,gs) ->
(a:as,b:bs,c:cs,d:ds,e:es,f:fs,g:gs))
([],[],[],[],[],[],[])
-
+-- | 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.
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]
deleteFirstsBy eq = foldl (flip (deleteBy eq))
-
--- group splits its list argument into a list of lists of equal, adjacent
--- elements. e.g.,
--- group "Mississippi" == ["M","i","ss","i","ss","i","pp","i"]
-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.
+group :: Eq a => [a] -> [[a]]
group = groupBy (==)
+-- | The 'groupBy' function is the non-overloaded version of 'group'.
groupBy :: (a -> a -> Bool) -> [a] -> [[a]]
groupBy _ [] = []
groupBy eq (x:xs) = (x:ys) : groupBy eq zs
where (ys,zs) = span (eq x) xs
--- inits xs returns the list of initial segments of xs, shortest first.
--- e.g., inits "abc" == ["","a","ab","abc"]
+-- | The 'inits' function returns all initial segments of the argument,
+-- shortest first. For example,
+--
+-- > inits "abc" == ["","a","ab","abc"]
+--
inits :: [a] -> [[a]]
inits [] = [[]]
inits (x:xs) = [[]] ++ map (x:) (inits xs)
--- tails xs returns the list of all final segments of xs, longest first.
--- e.g., tails "abc" == ["abc", "bc", "c",""]
+-- | The 'tails' function returns all final segments of the argument,
+-- longest first. For example,
+--
+-- > tails "abc" == ["abc", "bc", "c",""]
+--
tails :: [a] -> [[a]]
tails [] = [[]]
tails xxs@(_:xs) = xxs : tails xs
------------------------------------------------------------------------------
-- Quick Sort algorithm taken from HBC's QSort library.
+-- | 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.
sort :: (Ord a) => [a] -> [a]
+
+-- | The 'sortBy' function is the non-overloaded version of 'sort'.
sortBy :: (a -> a -> Ordering) -> [a] -> [a]
#ifdef USE_REPORT_PRELUDE
merge cmp [] ys = ys
merge cmp (x:xs) (y:ys)
= case x `cmp` y of
- LT -> x : merge cmp xs (y:ys)
- _ -> y : merge cmp (x:xs) ys
+ GT -> y : merge cmp (x:xs) ys
+ _ -> x : merge cmp xs (y:ys)
wrap :: a -> [a]
wrap x = [x]
#endif /* USE_REPORT_PRELUDE */
-{-
-\begin{verbatim}
- unfoldr f' (foldr f z xs) == (z,xs)
-
- if the following holds:
-
- f' (f x y) = Just (x,y)
- f' z = Nothing
-\end{verbatim}
--}
+-- | 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
unfoldr :: (b -> Maybe (a, b)) -> b -> [a]
unfoldr f b =
Just (a,new_b) -> a : unfoldr f new_b
Nothing -> []
-
-- -----------------------------------------------------------------------------
--- strict version of foldl
+-- | A strict version of 'foldl'.
foldl' :: (a -> b -> a) -> a -> [b] -> a
foldl' f a [] = a
foldl' f a (x:xs) = let a' = f a x in a' `seq` foldl' f a' xs
+#ifdef __GLASGOW_HASKELL__
-- -----------------------------------------------------------------------------
-- List sum and product
--- sum and product compute the sum or product of a finite list of numbers.
{-# SPECIALISE sum :: [Int] -> Int #-}
{-# SPECIALISE sum :: [Integer] -> Integer #-}
{-# SPECIALISE product :: [Int] -> Int #-}
{-# SPECIALISE product :: [Integer] -> Integer #-}
-sum, product :: (Num a) => [a] -> a
+-- | The 'sum' function computes the sum of a finite list of numbers.
+sum :: (Num a) => [a] -> a
+-- | The 'product' function computes the product of a finite list of numbers.
+product :: (Num a) => [a] -> a
#ifdef USE_REPORT_PRELUDE
sum = foldl (+) 0
product = foldl (*) 1
prod [] a = a
prod (x:xs) a = prod xs (a*x)
#endif
+
+-- -----------------------------------------------------------------------------
+-- Functions on strings
+
+-- | 'lines' breaks a string up into a list of strings at newline
+-- characters. The resulting strings do not contain newlines.
+lines :: String -> [String]
+lines "" = []
+lines s = let (l, s') = break (== '\n') s
+ in l : case s' of
+ [] -> []
+ (_:s'') -> lines s''
+
+-- | 'unlines' is an inverse operation to 'lines'.
+-- It joins lines, after appending a terminating newline to each.
+unlines :: [String] -> String
+#ifdef USE_REPORT_PRELUDE
+unlines = concatMap (++ "\n")
+#else
+-- HBC version (stolen)
+-- here's a more efficient version
+unlines [] = []
+unlines (l:ls) = l ++ '\n' : unlines ls
+#endif
+
+-- | 'words' breaks a string up into a list of words, which were delimited
+-- by white space.
+words :: String -> [String]
+words s = case dropWhile {-partain:Char.-}isSpace s of
+ "" -> []
+ s' -> w : words s''
+ where (w, s'') =
+ break {-partain:Char.-}isSpace s'
+
+-- | 'unwords' is an inverse operation to 'words'.
+-- It joins words with separating spaces.
+unwords :: [String] -> String
+#ifdef USE_REPORT_PRELUDE
+unwords [] = ""
+unwords ws = foldr1 (\w s -> w ++ ' ':s) ws
+#else
+-- HBC version (stolen)
+-- here's a more efficient version
+unwords [] = ""
+unwords [w] = w
+unwords (w:ws) = w ++ ' ' : unwords ws
+#endif
+#endif /* __GLASGOW_HASKELL__ */
projects / ghc-base.git / blobdiff