X-Git-Url: http://git.megacz.com/?a=blobdiff_plain;f=Data%2FList.hs;h=3e2bead03e480fa2cec95d1b93f4e24ac264240a;hb=0c5850d96fccf621aa3bcbc15135020bd54533c5;hp=63277f335579ec55904477bfaea6708e8ddf1139;hpb=00ad3706672e7d739be53af26c345500e44b0d70;p=ghc-base.git diff --git a/Data/List.hs b/Data/List.hs index 63277f3..3e2bead 100644 --- a/Data/List.hs +++ b/Data/List.hs @@ -15,6 +15,10 @@ module Data.List ( +#ifdef __NHC__ + [] (..) + , +#endif elemIndex -- :: (Eq a) => a -> [a] -> Maybe Int , elemIndices -- :: (Eq a) => a -> [a] -> [Int] @@ -132,6 +136,10 @@ module Data.List ) where +#ifdef __NHC__ +import Prelude hiding (Maybe(..)) +#endif + import Data.Maybe #ifdef __GLASGOW_HASKELL__ @@ -147,18 +155,32 @@ infix 5 \\ -- ----------------------------------------------------------------------------- -- List functions +-- | The 'elemIndex' function finds the first element in the given list +-- which is equal (by '(==)') to the query element. It returns the 0-based +-- index of that element. The function returns 'Nothing' if the element +-- is not found in the list. elemIndex :: Eq a => a -> [a] -> Maybe Int elemIndex x = findIndex (x==) +-- | The 'elemIndices' function behaves similarly to 'elemIndex', except +-- it returns the indices of all matching elements, not just the first. 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 no +-- such element exists. 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 elemen in the list matching the predicate, or +-- Nothing if no such element exists. findIndex :: (a -> Bool) -> [a] -> Maybe Int findIndex p = listToMaybe . findIndices p +-- | The 'findIndices' function behaves like 'findIndex', but returns +-- all matching indices. findIndices :: (a -> Bool) -> [a] -> [Int] #if defined(USE_REPORT_PRELUDE) || !defined(__GLASGOW_HASKELL__) @@ -172,6 +194,8 @@ findIndices p ls = loop 0# ls | otherwise = loop (n +# 1#) xs #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 @@ -181,6 +205,8 @@ 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 occurance of each element. (The name `nub' means `essence'.) nub :: (Eq a) => [a] -> [a] #ifdef USE_REPORT_PRELUDE nub = nubBy (==) @@ -194,6 +220,9 @@ nub l = nub' l [] -- ' | 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 [] = [] @@ -218,9 +247,13 @@ elem_by eq y (x:xs) = x `eq` y || elem_by eq y xs -- delete x removes the first occurrence of x from its list argument. +-- | The 'delete' function takes an element and a list and removes the +-- first occurance of the elemtn from the list. 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 @@ -228,29 +261,41 @@ 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. In particular, the +-- first occurance of each element of the second argument is +-- removed from the first argument (once). (\\) :: (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. +-- If the first list contains duplicates, so will the result. 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. +-- If the first list contains duplicates, so will the result. 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. intersperse :: a -> [a] -> [a] intersperse _ [] = [] intersperse _ [x] = [x] intersperse sep (x:xs) = x : sep : intersperse sep xs +-- | The 'transpose' function performs matrix transposition on its argument. transpose :: [[a]] -> [[a]] transpose [] = [] transpose ([] : xss) = transpose xss @@ -261,6 +306,9 @@ transpose ((x:xs) : xss) = (x : [h | (h:t) <- xss]) : transpose (xs : [ t | (h:t -- 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. partition :: (a -> Bool) -> [a] -> ([a],[a]) {-# INLINE partition #-} partition p xs = foldr (select p) ([],[]) xs @@ -274,6 +322,10 @@ select p x (ts,fs) | p x = (x:ts,fs) -- 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'. In particular, it applies a function to each element of alist, +-- 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 @@ -288,6 +340,10 @@ mapAccumL f s (x:xs) = (s'',y:ys) -- @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'. In particular, it applies a function to each element of alist, +-- 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 @@ -299,10 +355,14 @@ mapAccumR f s (x:xs) = (s'', y:ys) 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. 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') @@ -310,6 +370,9 @@ 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. +-- It is an error on an empty list. maximumBy :: (a -> a -> Ordering) -> [a] -> a maximumBy _ [] = error "List.maximumBy: empty list" maximumBy cmp xs = foldl1 max xs @@ -318,6 +381,9 @@ 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. +-- It is an error on an empty list. minimumBy :: (a -> a -> Ordering) -> [a] -> a minimumBy _ [] = error "List.minimumBy: empty list" minimumBy cmp xs = foldl1 min xs @@ -326,22 +392,31 @@ 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 _ [] = ([],[]) @@ -349,7 +424,8 @@ genericSplitAt n (x:xs) | n > 0 = (x:xs',xs'') where (xs',xs'') = genericSplitAt (n-1) xs genericSplitAt _ _ = error "List.genericSplitAt: negative argument" - +-- | The 'genericIndex' function is an overloaded version of 'index', which +-- accepts any Integral value as the index to return. genericIndex :: (Integral a) => [b] -> a -> b genericIndex (x:_) 0 = x genericIndex (_:xs) n @@ -357,69 +433,83 @@ 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 occurance of each element of the second list removed. deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a] deleteFirstsBy eq = foldl (flip (deleteBy eq)) @@ -427,9 +517,14 @@ 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"] +-- | 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, +-- when applied to the string \"Mississippi\", the result is @[\"M\",\"i\",\"ss\",\"i\",\"ss\",\"i\",\"pp\",\"i\"]@. 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 @@ -437,12 +532,14 @@ groupBy eq (x:xs) = (x:ys) : groupBy eq zs -- 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 segements of the argument, short to long. 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 segements of the argument, long to short. tails :: [a] -> [[a]] tails [] = [[]] tails xxs@(_:xs) = xxs : tails xs @@ -451,7 +548,9 @@ tails xxs@(_:xs) = xxs : tails xs ------------------------------------------------------------------------------ -- Quick Sort algorithm taken from HBC's QSort library. +-- | The 'sort' function sorts a list with the overloaded 'compare' 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 @@ -577,6 +676,10 @@ rqpart cmp x (y:ys) rle rgt r = \end{verbatim} -} +-- | The 'unfoldr' function produces a list from an element. 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. unfoldr :: (b -> Maybe (a, b)) -> b -> [a] unfoldr f b = case f b of @@ -587,11 +690,12 @@ unfoldr f b = -- ----------------------------------------------------------------------------- -- 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 -#ifndef __HUGS__ +#ifdef __GLASGOW_HASKELL__ -- ----------------------------------------------------------------------------- -- List sum and product @@ -602,16 +706,20 @@ foldl' f a (x:xs) = let a' = f a x in a' `seq` foldl' f a' xs {-# SPECIALISE product :: [Integer] -> Integer #-} sum, product :: (Num a) => [a] -> a #ifdef USE_REPORT_PRELUDE +-- | The 'sum' function sums the elements of a list. sum = foldl (+) 0 +-- | The 'product' function computes the product of the elements of a list. product = foldl (*) 1 #else +-- | The 'sum' function sums the elements of a list. sum l = sum' l 0 where sum' [] a = a sum' (x:xs) a = sum' xs (a+x) +-- | The 'product' function computes the product of the elements of a list. product l = prod l 1 where prod [] a = a prod (x:xs) a = prod xs (a*x) #endif -#endif /* __HUGS__ */ +#endif /* __GLASGOW_HASKELL__ */