Difference between revisions of "99 questions/Solutions/14"
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< 99 questions | Solutions
| Line 25: | Line 25: | ||
<haskell> | <haskell> | ||
dupli = concatMap (replicate 2) | dupli = concatMap (replicate 2) | ||
| + | </haskell> | ||
| + | |||
| + | or, using <hask>foldl</hask>: | ||
| + | <haskell> | ||
| + | dupli = foldl (\acc x -> acc ++ [x,x]) [] | ||
</haskell> | </haskell> | ||
Revision as of 22:26, 20 December 2010
(*) 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) []