CODEWITHSUNDEEP
listhaskell
Randall Lionel Kharkrang
Randall Lionel Kharkrang

Reputation: 1

Replicating through a list in Haskell

replicatee :: [a] -> Int -> [a]
replicatee [] _ = []
replicatee xs 0 = []
replicatee (x:xs) n = x:replicatee (x:xs) (n-1): replicatee xs n

So this is my code for replicating a an element in a list n times, the compler keeps showing an error :

Couldnt match type 'a'with [a], I'm seriously confused, please help out.

Edit : what i want my function to do is this: replicatee [1,2,3,4] 2

[1,1,2,2,3,3,4,4]

Upvotes: 0

Views: 76

Answers (2)

chepner
chepner

Reputation: 531868

replicatee :: [a] -> Int -> [a]
replicatee [] _ = []
replicatee xs 0 = []
replicatee (x:xs) n = x:replicatee (x:xs) (n-1): replicatee xs n

The problem is that replicatee returns a value of type [a], but you try to add that to another list of type [a] using (:) :: a -> [a] -> [a]. From a type-checking perspective, you need to use (++), not (:):

replicatee xs'@(x:xs) n = x : (replicatee xs' (n-1) ++ replicatee xs n)

Whether it does what you intended is another matter. Based on your description, Mikkel provides the right answer.

Upvotes: 0

Mikkel
Mikkel

Reputation: 782

I might have misunderstood your intention, but maybe you meant something like this:

replicatee :: a -> Int -> [a]
replicatee _ 0 = []
replicatee x n = x:replicatee x (n-1)

Upvotes: 1

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