Why am I getting type mismatch when my answer is a fraction?

Question

I am trying to find the dot quotient of two tuples through pattern matching in Haskell, which is dot(q,p) = q1/p1 + q2/p2 + q3/p3.

I keep getting this error in terminal when I run tupleDotQuotient (1, 2, 3) (1, 2, 3):

Couldn't match expected type ‘[p]’
                  with actual type ‘(a0, b0, c0)’
    • In the first argument of ‘tupleDotQuotient’, namely ‘(1, 2, 3)’
      In the expression: tupleDotQuotient (1, 2, 3) (1, 2, 3)
      In an equation for ‘it’: it = tupleDotQuotient (1, 2, 3) (1, 2, 3)
    • Relevant bindings include it :: p (bound at <interactive>:10:1)

I am new to Haskell and am not sure what the problem is. If I change it to Num p => [p] -> [p] -> p, I get an error in (x / y) since (/) is a part of Fraction type class. What can I do to improve this pattern matching to find the dot quotient of two tuples/vectors?

Answer 1

[p] is a list of ps, not a tuple. Call your function with actual lists:

tupleDotQuotient [1, 2, 3] [1, 2, 3]

You could implement a tupleDotQuotient for tuples, but you'd have to provide an overload for each tuple size - so don't. (On the other hand, using arbitrarily-sized lists means that you could pass two lists of different lengths to your function, so you'll need to handle that case).