CODEWITHSUNDEEP
haskell
cybertextron
cybertextron

Reputation: 10981

expected type different than actual type - Haskell

I have this simple method is Haskell, which dispenses much explanation: 

-- IgnoreAfter problem: ignoreAfter 3 [7,8,9,3,4,5] == [7,8,9].
ignoreAfter 0 xs = []
ignoreAfter n (x:xs) = if length((x:xs)) >= n then
                           x : ignoreAfter(n-1 xs)
                       else
                          []

I'm getting the following error:

pattern_matching.hs:19:32:
    Couldn't match expected type `[a0]' with actual type `[a0] -> [a0]'
    In the return type of a call of `ignoreAfter'
    Probable cause: `ignoreAfter' is applied to too few arguments
    In the second argument of `(:)', namely `ignoreAfter (n - 1 xs)'
    In the expression: x : ignoreAfter (n - 1 xs)
Failed, modules loaded: none.

Although I know the logic is sound, I can't figure out what I'm missing here ... could someone please help me out?

Upvotes: 1

Views: 104

Answers (1)

user224567893
user224567893

Reputation: 656

Change x : ignoreAfter(n-1 xs) to x : ignoreAfter (n-1) xs. () are not part of the function application in Haskell. When you passed (n-1 xs) to ignoreAfter, it treated it as just one argument. That is why you were getting the Probable cause: ignoreAfter is applied to too few arguments message.

Upvotes: 4

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