# 99 questions/Solutions/15

### From HaskellWiki

< 99 questions | Solutions(Difference between revisions)

m (Improved my version a little) |
|||

Line 38: | Line 38: | ||

repli (x:xs) n = foldr (const (x:)) (repli xs n) [1..n] |
repli (x:xs) n = foldr (const (x:)) (repli xs n) [1..n] |
||

</haskell> |
</haskell> |
||

+ | |||

+ | |||

+ | [[Category:Programming exercise spoilers]] |

## Latest revision as of 19:33, 18 January 2014

(**) Replicate the elements of a list a given number of times.

repli :: [a] -> Int -> [a] repli xs n = concatMap (replicate n) xs

or, in Pointfree style:

repli = flip $ concatMap . replicate

replicate

repli :: [a] -> Int -> [a] repli xs n = concatMap (take n . repeat) xs

or, using the list monad:

repli :: [a] -> Int -> [a] repli xs n = xs >>= replicate n

replicate

repli :: [a] -> Int -> [a] repli xs n = foldl (\acc e -> acc ++ repli' e n) [] xs where repli' _ 0 = [] repli' x n = x : repli' x (n-1)

or, a version that does not use list concatenation:

repli :: [a] -> Int -> [a] repli [] _ = [] repli (x:xs) n = foldr (const (x:)) (repli xs n) [1..n]