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11/06/2002 Entry: "Why I love functional programming more each day"

No Peaches for me last night. I wasted last night tracking down a compiler problem in a really stupid CS656 programming assignment. I love functional programming more each day. Death to the dreaded side effect ! Boring particulars in the extended section. Upshot is the c++ compiler we have to use for the course doesn't process the if statement in correctly.

What it boiled down to was


A = expr1;
if (f(A) == expr3) {
A = expr4;
} else if (g(A) == expr5) {
A = expr6;
}


What was happening was control was reaching the first conditional, so A=expr4, then it was falling into the second conditional as well, so instead of A having expr1 like it should have, it had expr4 now, and g(expr4) was expr5. Uggles !! When I changed it to


A = expr1;
B = A;
if (f(B) == expr3) {
A = expr4;
} else if (g(B) == expr5) {
A = expr6;
}


everything works fine because the value of B doesn't change in the middle of the first conditons processing. There's no chance that even if control reaches the second condition, which it shouldn't, it's in the else clause, dammit, it's value won't be impacted by the first condition block's processsing, since there's no assignments to B in it.

Grumble, grumble, grumble.