Question

foo:: Int -> Int -> Int
foo z x = if (z < 100) 
             then z * foo (z+(x*z)) z
             else z

How would you print out(the integer z) an output every time it gets called from itself?Can you have function that returns an IO and Int? Do you need a secondary function?

Answer 1

For simplicity, you can use trace. However it’s not welcomed for real production code as it breaks referential transparency.
trace takes a String to print and a value to return.

import Debug.Trace

foo:: Int -> Int -> Int
foo z x = trace ("z = " ++ show z) $ if (z < 100) 
    then z * foo (z+(x*z)) z
    else z

*Main> foo 1 2
 z = 1
 z = 3
 z = 6
 z = 24
 z = 168
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