While in a loop in Haskell

Question

How to code the following pseudo-code in Haskell?

x=0
for (i from 0 to 100):
    j=0
    while ( f(i,j) >0 ):
      x+= f(i,j)
      j+=1

(<

Answer 1

Here's a way that only computes f once for each pair:

inner i = sum $ takeWhile (> 0) $ map (f i) [0..]
x= sum $ map inner [0..100]

I dislike list comprehensions, especially for more complex expressions, so I found your solution difficult to read. The primary difference is that instead of storing a list of js such that f i j > 0, I stored the actual function value. This does no more work due to laziness.