How to define a variable based on an if/then/else statement

Question

I'm trying to translate some python code to haskell. However I reached a point where I'm not sure how to proceed.

if len(prod) % 2 == 0:
    ss = float(1.5 * count_vowels(cust))
else:
    ss = float(count_consonants(cust)) # muliplicaton by 1 is implied.

if len(cust_factors.intersection(prod_factors)) > 0:
    ss *= 1.5

return ss

I've tried to translate it to this:

if odd length prod
    then ss = countConsonants cust
    else ss = countVowels cust
if  length (cust intersect prod) > 0
    then ss = 1.5 * ss
    else Nothing

return ss

But I keep getting errors of:

parse error on input `='

Any help or words of wisdom on this would be greatly appreciated.

Answer 1

Don't think of programming in Haskell as "if this, then do that, then do the other thing" — the entire idea of doing things in a sequence is imperative. You're not checking a condition and then defining a variable — you're just calculating a result that depends on a condition. In functional programming, if is an expression and variables are assigned the result of an expression, not assigned inside it.

The most direct translation would be:

let ss = if odd $ length prod
         then countConsonants cust
         else countVowels cust
in if length (cust `intersect` prod) > 0
   then Just $ 1.5 * ss
   else Nothing