Difference between revisions of "99 questions/Solutions/14"
< 99 questions | Solutions
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<haskell> |
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− | dupli = foldr (\x -> |
+ | dupli = foldr (\x -> (x:) . (x:)) [] |
</haskell> |
</haskell> |
Revision as of 22:55, 19 January 2011
(*) Duplicate the elements of a list.
dupli [] = []
dupli (x:xs) = x:x:dupli xs
or, using list comprehension syntax:
dupli list = concat [[x,x] | x <- list]
or, using the list monad:
dupli xs = xs >>= (\x -> [x,x])
or, using concatMap
:
dupli = concatMap (\x -> [x,x])
also using concatMap
:
dupli = concatMap (replicate 2)
or, using foldl
:
dupli = foldl (\acc x -> acc ++ [x,x]) []
or, using foldr
:
dupli = foldr (\ x xs -> x : x : xs) []
or, using applicative functors:
dupli xs = (++) <$> xs <*> xs
or, using silliness:
dupli = foldr (\x -> (x:) . (x:)) []