Question

first I’d like to appreciate your time answering my question.

First, please take a quick look at my code. You don’t have to understand the code, just pay attention to the types.

This return an error that says,

Couldn't match expected type `Int' with actual type `Integer'
Expected type: [Int]
  Actual type: [Integer]
In the first argument of `myfun', namely `primes'
In the expression: myfun primes

Failed, modules loaded: none.

I can run this successfully with no error if I change the types to Int instead of Integer, so for example, “primes :: [Int]”

However, I am required to keep it integer for the program to be able to take large numbers.

Thank you very much for your help in advance.

Answer 1

The error is coming from (!!) in myfun:

myfun (a:ab) = fibs !! (a-1) : myfun(ab)

which a newer GHC would have probably informed you about (I think). Try this:

myfun (a:ab) = fibs !! ((fromInteger a)-1) : myfun(ab)

fromInteger is polymorphic in its result type, so here the type system infers you want an Int. hoogle knows a lot about these kind of questions.