Re: Nested list comprehension

[miran]

There are few problems with your Nim version, e.g. returning `string` instead 
of `seq[string]` (cause this is what the Python version does - it returns a 
list).

Here is a correct Nim version: 
    
    
    proc cross(xs, ys: string): seq[string] =
      ## Cross product of elements in A and elements in B.
      for x in xs:
        for y in ys:
          result.add x&y
    
    
    Run