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<a name="sect17"></a>
<h2>17<tt> </tt>List Utilities</h2><p>
<table border=2 cellpadding=3>
<tr><td>
<tt><br>
module List ( <br>
elemIndex, elemIndices,<br>
find, findIndex, findIndices,<br>
nub, nubBy, delete, deleteBy, (\\), deleteFirstsBy,<br>
union, unionBy, intersect, intersectBy,<br>
intersperse, transpose, partition, group, groupBy,<br>
inits, tails, isPrefixOf, isSuffixOf,<br>
mapAccumL, mapAccumR,<br>
sort, sortBy, insert, insertBy, maximumBy, minimumBy,<br>
genericLength, genericTake, genericDrop,<br>
genericSplitAt, genericIndex, genericReplicate,<br>
zip4, zip5, zip6, zip7,<br>
zipWith4, zipWith5, zipWith6, zipWith7,<br>
unzip4, unzip5, unzip6, unzip7, unfoldr,<br>
<br>
-- ...and what the Prelude exports<br>
-- []((:), []), -- This is built-in syntax<br>
map, (++), concat, filter,<br>
head, last, tail, init, null, length, (!!),<br>
foldl, foldl1, scanl, scanl1, foldr, foldr1, scanr, scanr1,<br>
iterate, repeat, replicate, cycle,<br>
take, drop, splitAt, takeWhile, dropWhile, span, break,<br>
lines, words, unlines, unwords, reverse, and, or,<br>
any, all, elem, notElem, lookup,<br>
sum, product, maximum, minimum, concatMap, <br>
zip, zip3, zipWith, zipWith3, unzip, unzip3<br>
) where<br>
<br>
infix 5 \\<br>
<br>
elemIndex :: Eq a => a -> [a] -> Maybe Int<br>
elemIndices :: Eq a => a -> [a] -> [Int]<br>
find :: (a -> Bool) -> [a] -> Maybe a<br>
findIndex :: (a -> Bool) -> [a] -> Maybe Int<br>
findIndices :: (a -> Bool) -> [a] -> [Int]<br>
nub :: Eq a => [a] -> [a]<br>
nubBy :: (a -> a -> Bool) -> [a] -> [a]<br>
delete :: Eq a => a -> [a] -> [a]<br>
deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]<br>
(\\) :: Eq a => [a] -> [a] -> [a]<br>
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
union :: Eq a => [a] -> [a] -> [a]<br>
unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
<br>
</tt></td></tr></table>
<table border=2 cellpadding=3>
<tr><td>
<tt><br>
intersect :: Eq a => [a] -> [a] -> [a]<br>
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
intersperse :: a -> [a] -> [a]<br>
transpose :: [[a]] -> [[a]]<br>
partition :: (a -> Bool) -> [a] -> ([a],[a])<br>
group :: Eq a => [a] -> [[a]]<br>
groupBy :: (a -> a -> Bool) -> [a] -> [[a]]<br>
inits :: [a] -> [[a]] <br>
tails :: [a] -> [[a]] <br>
isPrefixOf :: Eq a => [a] -> [a] -> Bool<br>
isSuffixOf :: Eq a => [a] -> [a] -> Bool<br>
mapAccumL :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])<br>
mapAccumR :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])<br>
unfoldr :: (b -> Maybe (a,b)) -> b -> [a]<br>
sort :: Ord a => [a] -> [a]<br>
sortBy :: (a -> a -> Ordering) -> [a] -> [a]<br>
insert :: Ord a => a -> [a] -> [a]<br>
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]<br>
maximumBy :: (a -> a -> Ordering) -> [a] -> a<br>
minimumBy :: (a -> a -> Ordering) -> [a] -> a<br>
genericLength :: Integral a => [b] -> a<br>
genericTake :: Integral a => a -> [b] -> [b]<br>
genericDrop :: Integral a => a -> [b] -> [b]<br>
genericSplitAt :: Integral a => a -> [b] -> ([b],[b])<br>
genericIndex :: Integral a => [b] -> a -> b<br>
genericReplicate :: Integral a => a -> b -> [b]<br>
<br>
zip4 :: [a] -> [b] -> [c] -> [d] -> [(a,b,c,d)]<br>
zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a,b,c,d,e)]<br>
zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] <br>
-> [(a,b,c,d,e,f)]<br>
zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> [g]<br>
-> [(a,b,c,d,e,f,g)]<br>
zipWith4 :: (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]<br>
zipWith5 :: (a->b->c->d->e->f) -> <br>
[a]->[b]->[c]->[d]->[e]->[f]<br>
zipWith6 :: (a->b->c->d->e->f->g) -><br>
[a]->[b]->[c]->[d]->[e]->[f]->[g]<br>
zipWith7 :: (a->b->c->d->e->f->g->h) -><br>
[a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]<br>
unzip4 :: [(a,b,c,d)] -> ([a],[b],[c],[d])<br>
unzip5 :: [(a,b,c,d,e)] -> ([a],[b],[c],[d],[e])<br>
unzip6 :: [(a,b,c,d,e,f)] -> ([a],[b],[c],[d],[e],[f])<br>
unzip7 :: [(a,b,c,d,e,f,g)] -> ([a],[b],[c],[d],[e],[f],[g])<br>
</tt></td></tr></table>
<p>
This library defines some lesser-used operations over lists.<p>
<a name="sect17.1"></a>
<h3>17.1<tt> </tt>Indexing lists</h3><p>
<UL><LI><tt>elemIndex val list</tt> returns the index of
the first occurrence, if any, of <tt>val</tt>
in <tt>list</tt> as <tt>Just index</tt>. <tt>Nothing</tt> is returned if <tt>not (val `elem` list)</tt>.<p>
<LI><tt>elemIndices val list</tt> returns an
in-order list of indices, giving the occurrences of <tt>val</tt> in <tt>list</tt>.<p>
<LI><tt>find</tt>
returns the first element of a list that satisfies a predicate,
or Nothing, if there is no such element.
<tt>findIndex</tt> returns the corresponding index.
<tt>findIndices</tt> returns a list of all such indices.
</UL><p>
<a name="sect17.2"></a>
<h3>17.2<tt> </tt>"Set" operations</h3><p>
There are a number of "set" operations defined over the <tt>List</tt> type.
<tt>nub</tt> (meaning "essence") removes duplicates elements from a list.
<tt>delete</tt>, <tt>(\\)</tt>, <tt>union</tt> and <tt>intersect</tt> (and their <tt>By</tt> variants)
preserve the invariant that their result
does not contain duplicates, provided that their first argument
contains no duplicates.<p>
<UL><LI>
<tt>nub</tt> removes duplicate elements from a list. For example:
<tt><br>
<br>
nub [1,3,1,4,3,3] = [1,3,4]<br>
<br>
</tt><LI>
<tt>delete x</tt>
removes the first occurrence of <tt>x</tt> from its list argument,
e.g.,
<tt><br>
<br>
delete 'a' "banana" == "bnana"<br>
<br>
<p>
</tt><LI>
<tt>(\\)</tt> is list
difference (non-associative). In the result of <tt>xs \\ ys</tt>,
the first occurrence of each element of <tt>ys</tt> in turn (if any)
has been removed from <tt>xs</tt>. Thus, <tt>(xs ++ ys) \\ xs == ys</tt>.<p>
<LI>
<tt>union</tt> is list union, e.g.,
<tt><br>
<br>
"dog" `union` "cow" == "dogcw"<br>
<br>
<p>
</tt><LI>
<tt>intersect</tt> is list intersection, e.g.,
<tt><br>
<br>
[1,2,3,4] `intersect` [2,4,6,8] == [2,4]<br>
<br>
</tt></UL><p>
<a name="sect17.3"></a>
<h3>17.3<tt> </tt>List transformations</h3><p>
<UL><LI>
<tt>intersperse sep</tt>
inserts <tt>sep</tt> between the elements of its list argument,
e.g.,
<tt><br>
<br>
intersperse ',' "abcde" == "a,b,c,d,e"<br>
<br>
<p>
</tt><LI>
<tt>transpose</tt> transposes the rows and columns of its argument,
e.g.,
<tt><br>
<br>
transpose [[1,2,3],[4,5,6]] == [[1,4],[2,5],[3,6]]<br>
<br>
<p>
</tt><LI>
<tt>partition</tt>
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.,
<tt><br>
<br>
partition p xs == (filter p xs, filter (not . p) xs)<br>
<br>
<p>
</tt><LI>
<tt>sort
</tt>implement a stable sorting algorithm, here specified
in terms of the <tt>insertBy</tt> function, which inserts objects into a list
according to the specified ordering relation.<p>
<LI>
<tt>insert
</tt>inserts a new element into an <I>ordered</I> list (arranged in increasing order).<p>
<LI>
<tt>group</tt> splits its list argument into a list of lists of equal, adjacent
elements. For example
<tt><br>
<br>
group "Mississippi" == ["M","i","ss","i","ss","i","pp","i"]<br>
<br>
<p>
</tt><LI>
<tt>inits</tt> returns the list of initial segments of its argument list, shortest first.
<tt><br>
<br>
inits "abc" == ["","a","ab","abc"]<br>
<br>
<p>
</tt><LI>
<tt>tails</tt>
returns the list of all final segments of its argument list, longest first.
<tt><br>
<br>
tails "abc" == ["abc", "bc", "c",""]<br>
<p>
<br>
</tt><LI>
<tt>mapAccumL f s l</tt>
applies <tt>f</tt> to an accumulating "state" parameter <tt>s
</tt>and to each element of <tt>l</tt> in turn.<p>
<LI>
<tt>mapAccumR
</tt>is similar to <tt>mapAccumL</tt> except that the list
is processed from right-to-left rather than left-to-right.
</UL><p>
<a name="sect17.4"></a>
<h3>17.4<tt> unfoldr</tt></h3><p>
The <tt>unfoldr</tt> function is a "dual" to <tt>foldr</tt>: while <tt>foldr</tt> reduces a list
to a summary value, <tt>unfoldr</tt> builds a list from a seed value. For
example:
<tt><br>
<br>
iterate f == unfoldr (\x -> Just (x, f x))<br>
<br>
</tt>In some cases, <tt>unfoldr</tt> can undo a <tt>foldr</tt> operation:
<tt><br>
<br>
unfoldr f' (foldr f z xs) == xs<br>
<br>
</tt>if the following holds:
<tt><br>
<br>
f' (f x y) = Just (x,y)<br>
f' z = Nothing<br>
<br>
<p>
</tt><a name="sect17.5"></a>
<h3>17.5<tt> </tt>Predicates</h3><p>
<tt>isPrefixOf</tt> and <tt>isSuffixOf</tt> check whether the first argument is a prefix (resp. suffix)
of the second argument.<p>
<a name="sect17.6"></a>
<h3>17.6<tt> </tt>The "<tt>By</tt>" operations</h3><p>
By convention, overloaded functions have a non-overloaded
counterpart whose name is suffixed with "<tt>By</tt>". For example, the
function <tt>nub</tt> could be defined as follows:
<tt><br>
<br>
nub :: (Eq a) => [a] -> [a]<br>
nub [] = []<br>
nub (x:xs) = x : nub (filter (\y -> not (x == y)) xs)<br>
<br>
</tt>However, the equality method may not be appropriate in all situations.
The function:
<tt><br>
<br>
nubBy :: (a -> a -> Bool) -> [a] -> [a]<br>
nubBy eq [] = []<br>
nubBy eq (x:xs) = x : nubBy eq (filter (\y -> not (eq x y)) xs)<br>
<br>
</tt>allows the programmer to supply their own equality test.
When the "<tt>By</tt>" function replaces an <tt>Eq</tt> context by a binary predicate,
the predicate is assumed to define an equivalence; when the "<tt>By</tt>"
function replaces an <tt>Ord</tt> context by a binary predicate, the
predicate is assumed to define a total ordering.<p>
The "<tt>By</tt>" variants are as follows:
<tt>nubBy</tt>, <tt>deleteBy</tt>, <tt>deleteFirstsBy</tt> (the <tt>By</tt> variant of <tt>\\</tt>),
<tt>unionBy</tt>, <tt>intersectBy</tt>, <tt>groupBy</tt>,
<tt>sortBy</tt>, <tt>insertBy</tt>, <tt>maximumBy</tt>, <tt>minimumBy</tt>.
<p>
The library does not
provide <tt>elemBy</tt>, because <tt>any (eq x)</tt> does the same job as <tt>elemBy eq x</tt> would.
A handful of overloaded functions (<tt>elemIndex</tt>, <tt>elemIndices</tt>, <tt>isPrefixOf</tt>, <tt>isSuffixOf</tt>)
were not considered important enough to have "<tt>By</tt>" variants.<p>
<a name="sect17.7"></a>
<h3>17.7<tt> </tt>The "<tt>generic</tt>" operations</h3><p>
The prefix "<tt>generic</tt>" indicates an overloaded function that is
a generalised version of a <tt>Prelude</tt> function. For example,
<tt><br>
<br>
genericLength :: Integral a => [b] -> a<br>
</tt>
<tt><br>
</tt>is a generalised version of <tt>length</tt>.<p>
The "<tt>generic</tt>" operations are as follows:
<tt>genericLength</tt>, <tt>genericTake</tt>, <tt>genericDrop</tt>,
<tt>genericSplitAt</tt>, <tt>genericIndex</tt> (the generic version of <tt>!!</tt>), <tt>genericReplicate</tt>.<p>
<a name="sect17.8"></a>
<h3>17.8<tt> </tt>Further "<tt>zip</tt>" operations</h3><p>
The Prelude provides <tt>zip</tt>, <tt>zip3</tt>, <tt>unzip</tt>, <tt>unzip3</tt>, <tt>zipWith</tt>, and <tt>zipWith3</tt>.
The List library provides these same three operations for 4, 5, 6, and 7 arguments.<a name="List"></a><p>
<a name="sect17.9"></a>
<h3>17.9<tt> </tt>Library <tt>List</tt></h3>
<tt><br>
module List ( <br>
elemIndex, elemIndices,<br>
find, findIndex, findIndices,<br>
nub, nubBy, delete, deleteBy, (\\), deleteFirstsBy,<br>
union, unionBy, intersect, intersectBy,<br>
intersperse, transpose, partition, group, groupBy,<br>
inits, tails, isPrefixOf, isSuffixOf,<br>
mapAccumL, mapAccumR,<br>
sort, sortBy, insert, insertBy, maximumBy, minimumBy,<br>
genericLength, genericTake, genericDrop,<br>
genericSplitAt, genericIndex, genericReplicate,<br>
zip4, zip5, zip6, zip7,<br>
zipWith4, zipWith5, zipWith6, zipWith7,<br>
unzip4, unzip5, unzip6, unzip7, unfoldr,<br>
<br>
-- ...and what the Prelude exports<br>
-- []((:), []), -- This is built-in syntax<br>
map, (++), concat, filter,<br>
head, last, tail, init, null, length, (!!),<br>
foldl, foldl1, scanl, scanl1, foldr, foldr1, scanr, scanr1,<br>
iterate, repeat, replicate, cycle,<br>
take, drop, splitAt, takeWhile, dropWhile, span, break,<br>
lines, words, unlines, unwords, reverse, and, or,<br>
any, all, elem, notElem, lookup,<br>
sum, product, maximum, minimum, concatMap, <br>
zip, zip3, zipWith, zipWith3, unzip, unzip3<br>
) where<br>
<br>
import Maybe( listToMaybe )<br>
<br>
infix 5 \\<br>
<br>
elemIndex :: Eq a => a -> [a] -> Maybe Int<br>
elemIndex x = findIndex (x ==)<br>
<br>
elemIndices :: Eq a => a -> [a] -> [Int]<br>
elemIndices x = findIndices (x ==)<br>
<br>
find :: (a -> Bool) -> [a] -> Maybe a<br>
find p = listToMaybe . filter p<br>
<br>
findIndex :: (a -> Bool) -> [a] -> Maybe Int<br>
findIndex p = listToMaybe . findIndices p<br>
<br>
findIndices :: (a -> Bool) -> [a] -> [Int]<br>
findIndices p xs = [ i | (x,i) <- zip xs [0..], p x ]<br>
<br>
nub :: Eq a => [a] -> [a]<br>
nub = nubBy (==)<br>
<br>
nubBy :: (a -> a -> Bool) -> [a] -> [a]<br>
nubBy eq [] = []<br>
nubBy eq (x:xs) = x : nubBy eq (filter (\y -> not (eq x y)) xs)<br>
<br>
delete :: Eq a => a -> [a] -> [a]<br>
delete = deleteBy (==)<br>
<br>
deleteBy :: (a -> a -> Bool) -> a -> [a] -> [a]<br>
deleteBy eq x [] = []<br>
deleteBy eq x (y:ys) = if x `eq` y then ys else y : deleteBy eq x ys<br>
<br>
(\\) :: Eq a => [a] -> [a] -> [a]<br>
(\\) = foldl (flip delete)<br>
<br>
deleteFirstsBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
deleteFirstsBy eq = foldl (flip (deleteBy eq))<br>
<br>
union :: Eq a => [a] -> [a] -> [a]<br>
union = unionBy (==) <br>
<br>
unionBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
unionBy eq xs ys = xs ++ deleteFirstsBy eq (nubBy eq ys) xs<br>
<br>
intersect :: Eq a => [a] -> [a] -> [a]<br>
intersect = intersectBy (==)<br>
<br>
intersectBy :: (a -> a -> Bool) -> [a] -> [a] -> [a]<br>
intersectBy eq xs ys = [x | x <- xs, any (eq x) ys]<br>
<br>
intersperse :: a -> [a] -> [a]<br>
intersperse sep [] = []<br>
intersperse sep [x] = [x]<br>
intersperse sep (x:xs) = x : sep : intersperse sep xs<br>
<br>
-- transpose is lazy in both rows and columns,<br>
-- and works for non-rectangular 'matrices'<br>
-- For example, transpose [[1,2],[3,4,5],[]] = [[1,3],[2,4],[5]]<br>
-- Note that [h | (h:t) <- xss] is not the same as (map head xss)<br>
-- because the former discards empty sublists inside xss<br>
transpose :: [[a]] -> [[a]]<br>
transpose [] = []<br>
transpose ([] : xss) = transpose xss<br>
transpose ((x:xs) : xss) = (x : [h | (h:t) <- xss]) : <br>
transpose (xs : [t | (h:t) <- xss])<br>
<br>
partition :: (a -> Bool) -> [a] -> ([a],[a])<br>
partition p xs = (filter p xs, filter (not . p) xs)<br>
<br>
-- group splits its list argument into a list of lists of equal, adjacent<br>
-- elements. e.g.,<br>
-- group "Mississippi" == ["M","i","ss","i","ss","i","pp","i"]<br>
group :: Eq a => [a] -> [[a]]<br>
group = groupBy (==)<br>
<br>
groupBy :: (a -> a -> Bool) -> [a] -> [[a]]<br>
groupBy eq [] = []<br>
groupBy eq (x:xs) = (x:ys) : groupBy eq zs<br>
where (ys,zs) = span (eq x) xs<br>
<br>
-- inits xs returns the list of initial segments of xs, shortest first.<br>
-- e.g., inits "abc" == ["","a","ab","abc"]<br>
inits :: [a] -> [[a]]<br>
inits [] = [[]]<br>
inits (x:xs) = [[]] ++ map (x:) (inits xs)<br>
<br>
-- tails xs returns the list of all final segments of xs, longest first.<br>
-- e.g., tails "abc" == ["abc", "bc", "c",""]<br>
tails :: [a] -> [[a]]<br>
tails [] = [[]]<br>
tails xxs@(_:xs) = xxs : tails xs<br>
<br>
isPrefixOf :: Eq a => [a] -> [a] -> Bool<br>
isPrefixOf [] _ = True<br>
isPrefixOf _ [] = False<br>
isPrefixOf (x:xs) (y:ys) = x == y && isPrefixOf xs ys<br>
<br>
isSuffixOf :: Eq a => [a] -> [a] -> Bool<br>
isSuffixOf x y = reverse x `isPrefixOf` reverse y<br>
<br>
mapAccumL :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])<br>
mapAccumL f s [] = (s, [])<br>
mapAccumL f s (x:xs) = (s'',y:ys)<br>
where (s', y ) = f s x<br>
(s'',ys) = mapAccumL f s' xs<br>
<br>
mapAccumR :: (a -> b -> (a, c)) -> a -> [b] -> (a, [c])<br>
mapAccumR f s [] = (s, [])<br>
mapAccumR f s (x:xs) = (s'', y:ys)<br>
where (s'',y ) = f s' x<br>
(s', ys) = mapAccumR f s xs<br>
<br>
unfoldr :: (b -> Maybe (a,b)) -> b -> [a]<br>
unfoldr f b = case f b of<br>
Nothing -> []<br>
Just (a,b) -> a : unfoldr f b<br>
<br>
sort :: (Ord a) => [a] -> [a]<br>
sort = sortBy compare<br>
<br>
sortBy :: (a -> a -> Ordering) -> [a] -> [a]<br>
sortBy cmp = foldr (insertBy cmp) []<br>
<br>
insert :: (Ord a) => a -> [a] -> [a]<br>
insert = insertBy compare<br>
<br>
insertBy :: (a -> a -> Ordering) -> a -> [a] -> [a]<br>
insertBy cmp x [] = [x]<br>
insertBy cmp x ys@(y:ys')<br>
= case cmp x y of<br>
GT -> y : insertBy cmp x ys'<br>
_ -> x : ys<br>
<br>
maximumBy :: (a -> a -> Ordering) -> [a] -> a<br>
maximumBy cmp [] = error "List.maximumBy: empty list"<br>
maximumBy cmp xs = foldl1 max xs<br>
where<br>
max x y = case cmp x y of<br>
GT -> x<br>
_ -> y<br>
<br>
minimumBy :: (a -> a -> Ordering) -> [a] -> a<br>
minimumBy cmp [] = error "List.minimumBy: empty list"<br>
minimumBy cmp xs = foldl1 min xs<br>
where<br>
min x y = case cmp x y of<br>
GT -> y<br>
_ -> x<br>
<br>
genericLength :: (Integral a) => [b] -> a<br>
genericLength [] = 0<br>
genericLength (x:xs) = 1 + genericLength xs<br>
<br>
genericTake :: (Integral a) => a -> [b] -> [b]<br>
genericTake n _ | n <= 0 = []<br>
genericTake _ [] = []<br>
genericTake n (x:xs) = x : genericTake (n-1) xs<br>
<br>
genericDrop :: (Integral a) => a -> [b] -> [b]<br>
genericDrop n xs | n <= 0 = xs<br>
genericDrop _ [] = []<br>
genericDrop n (_:xs) = genericDrop (n-1) xs<br>
<br>
genericSplitAt :: (Integral a) => a -> [b] -> ([b],[b])<br>
genericSplitAt n xs | n <= 0 = ([],xs)<br>
genericSplitAt _ [] = ([],[])<br>
genericSplitAt n (x:xs) = (x:xs',xs'') where<br>
(xs',xs'') = genericSplitAt (n-1) xs<br>
<br>
genericIndex :: (Integral a) => [b] -> a -> b<br>
genericIndex (x:_) 0 = x<br>
genericIndex (_:xs) n <br>
| n > 0 = genericIndex xs (n-1)<br>
| otherwise = error "List.genericIndex: negative argument"<br>
genericIndex _ _ = error "List.genericIndex: index too large"<br>
<br>
genericReplicate :: (Integral a) => a -> b -> [b]<br>
genericReplicate n x = genericTake n (repeat x)<br>
<br>
zip4 :: [a] -> [b] -> [c] -> [d] -> [(a,b,c,d)]<br>
zip4 = zipWith4 (,,,)<br>
<br>
zip5 :: [a] -> [b] -> [c] -> [d] -> [e] -> [(a,b,c,d,e)]<br>
zip5 = zipWith5 (,,,,)<br>
<br>
zip6 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -> <br>
[(a,b,c,d,e,f)]<br>
zip6 = zipWith6 (,,,,,)<br>
<br>
zip7 :: [a] -> [b] -> [c] -> [d] -> [e] -> [f] -><br>
[g] -> [(a,b,c,d,e,f,g)]<br>
zip7 = zipWith7 (,,,,,,)<br>
<br>
zipWith4 :: (a->b->c->d->e) -> [a]->[b]->[c]->[d]->[e]<br>
zipWith4 z (a:as) (b:bs) (c:cs) (d:ds)<br>
= z a b c d : zipWith4 z as bs cs ds<br>
zipWith4 _ _ _ _ _ = []<br>
<br>
zipWith5 :: (a->b->c->d->e->f) -> <br>
[a]->[b]->[c]->[d]->[e]->[f]<br>
zipWith5 z (a:as) (b:bs) (c:cs) (d:ds) (e:es)<br>
= z a b c d e : zipWith5 z as bs cs ds es<br>
zipWith5 _ _ _ _ _ _ = []<br>
<br>
zipWith6 :: (a->b->c->d->e->f->g) -><br>
[a]->[b]->[c]->[d]->[e]->[f]->[g]<br>
zipWith6 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs)<br>
= z a b c d e f : zipWith6 z as bs cs ds es fs<br>
zipWith6 _ _ _ _ _ _ _ = []<br>
<br>
zipWith7 :: (a->b->c->d->e->f->g->h) -><br>
[a]->[b]->[c]->[d]->[e]->[f]->[g]->[h]<br>
zipWith7 z (a:as) (b:bs) (c:cs) (d:ds) (e:es) (f:fs) (g:gs)<br>
= z a b c d e f g : zipWith7 z as bs cs ds es fs gs<br>
zipWith7 _ _ _ _ _ _ _ _ = []<br>
<br>
unzip4 :: [(a,b,c,d)] -> ([a],[b],[c],[d])<br>
unzip4 = foldr (\(a,b,c,d) ~(as,bs,cs,ds) -><br>
(a:as,b:bs,c:cs,d:ds))<br>
([],[],[],[])<br>
<br>
unzip5 :: [(a,b,c,d,e)] -> ([a],[b],[c],[d],[e])<br>
unzip5 = foldr (\(a,b,c,d,e) ~(as,bs,cs,ds,es) -><br>
(a:as,b:bs,c:cs,d:ds,e:es))<br>
([],[],[],[],[])<br>
<br>
unzip6 :: [(a,b,c,d,e,f)] -> ([a],[b],[c],[d],[e],[f])<br>
unzip6 = foldr (\(a,b,c,d,e,f) ~(as,bs,cs,ds,es,fs) -><br>
(a:as,b:bs,c:cs,d:ds,e:es,f:fs))<br>
([],[],[],[],[],[])<br>
<br>
unzip7 :: [(a,b,c,d,e,f,g)] -> ([a],[b],[c],[d],[e],[f],[g])<br>
unzip7 = foldr (\(a,b,c,d,e,f,g) ~(as,bs,cs,ds,es,fs,gs) -><br>
(a:as,b:bs,c:cs,d:ds,e:es,f:fs,g:gs))<br>
([],[],[],[],[],[],[])<br>
<p>
<hr><i>The Haskell 98 Report</i><br><a href="index.html">top</a> | <a href="array.html">back</a> | <a href="maybe.html">next</a> | <a href="index98.html">contents</a> | <a href="prelude-index.html">function index</a> <br><font size=2>December 2002</font>
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