CODEWITHSUNDEEP
haskell
devFox
devFox

Reputation: 33

Haskell Pascal's triangle

I have to create a recursive function that takes in two numbers (n and k) and gives back their binomial coefficient.

I have to use pascal :: Int -> Int -> Int

I honestly don't understand where it went wrong, thanks for the help!

pascal :: Int -> Int -> Int
pascal n k
      | k == 0 = 1
      | n == n = 1
      | k > n  = 0
      | otherwise = pascal(n-1)(k-1) + pascal(n-1) + k

The following error is:

main.hs:7:40: error:
    • Couldn't match expected type ‘Int’ with actual type ‘Int -> Int’
    • Probable cause: ‘pascal’ is applied to too few arguments
      In the second argument of ‘(+)’, namely ‘pascal (n - 1)’
      In the first argument of ‘(+)’, namely
        ‘pascal (n - 1) (k - 1) + pascal (n - 1)’
      In the expression: pascal (n - 1) (k - 1) + pascal (n - 1) + k
  |
7 |       | otherwise = pascal(n-1)(k-1) + pascal(n-1) + k
  |                                        ^^^^^^^^^^^
<interactive>:3:1: error:
    • Variable not in scope: main
    • Perhaps you meant ‘min’ (imported from Prelude)

Upvotes: 2

Views: 425

Answers (1)

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476659

As the exception says, pascal (n-1) does not make much sense, since that is a function Int -> Int, so you can not add pascal (n-1) (k-1) and pascal (n-1) together.

You thus need to pass an extra parameter. For example:

pascal :: Int -> Int -> Int
pascal _ 0 = 1
pascal n k
      | k == n = 1
      | k > n = 0
      | otherwise = pascal (n-1) (k-1) + pascal (n-1) k

Note that the condition n == n is always true, you probably want to say n == k?

Upvotes: 5

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