CODEWITHSUNDEEP
haskellpattern-matching
SR23
SR23

Reputation: 49

Why do I get "non-exhaustive patterns in function"?

In the following code Haskell complains about 

Non-exhaustive patterns in function prime'
prime :: Int -> [Int]
prime x = prime' [2..x] where
  prime' (p:ps)= p : prime' [x | x <- ps, mod x p > 0 && prime'' x [2..div x 2]]     
  prime'' _ [] = True
  prime'' n (x:xs)
    | mod n x == 0 = False
    |    otherwise = prime'' n xs

prime' []=[]

I can't find my mistake. Could someone explain why this happens, and what it means?

Upvotes: 0

Views: 702

Answers (1)

Zeta
Zeta

Reputation: 105955

Indentation. The last line defines another function called prime'. Therefore, prime\prime' (the definition in the where clause of prime) doesn't have a matching pattern for the empty list.

Also, you're indentation is all over the place. Do you still mix tabs and spaces?

Upvotes: 6

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