Side effects in the Zark extracts

Transcribed from the printed issue; not yet reviewed. Read it in the PDF of the issue, page 112

One aspect of the style of coding in the Zark extracts that I find difficult is the way functions are defined which return a result and also update one or more global variables. In Vol. 17 No 3 there was a typical example where the function COMMA∆MAT both returns a result and assigns a global variable fieldwidths. Of course, with a nested array APL one just returns the two items wrapped up as a two element vector and the function becomes ‘pure’ without any side effects. I think my displeasure is due to the fact that I have used nested arrays for such a long time that seeing a function with side effects is instantly categorised as being poorly coded. I find it quite difficult to remember how I attempted to solve the dilemma of multiple results with a non-nested APL, but I think I tried to make a clear separation between functions returning results and those which did not return a result. Only the non result returning functions were allowed to update or assign global variables. I have thrown away all my old code now, so I can’t tell if my memory is correct!