The Nim way to do this

[jzakiya]

I've looked through the docs but haven't found the answer to this.

I have an array of integers (prime numbers) and I want to: 1) determine if some 
number is included in the array and 2) return the index value of the number in 
the array.

In Ruby/Crystal I can do the following. What are the equivalent method(s) in 
Nim?
    
    
    Ruby
    
    1) primes = [7, 11, 13, 17, 19, 23, 29, 31]
    
    if primes.include? num; do_something_here end
    
    2) index = primes.index num
    
    

I tried to do the following in Nim to give me the equivalent result for 1) in 
Nim, but the compiler squawks.
    
    
    Nim
    
    1) if count(primes, num) == 1: do_something_here
    
    

I expected that `count(primes, num)` would return `0` if `num` isn't in 
`primes` but the compiler gives type mismatch error.