Re^7: resetting a foreach loop!

... if statements ... aren't expressions ...

if statements aren't expressions, but an
if (CONDITION) { ... }
statement must evaluate the CONDITION expression, and if that's the last expression evaluated in a subroutine (because it evaluates false), I thought that's what must be returned. At least, whenever I've encountered this situation, that's the way it's worked. (I don't like implicit returns myself and never use them, but just sayin' ...) I'd be interested to learn more about this.

Give a man a fish: <%-{-{-{-<

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Re^8: resetting a foreach loop! by pryrt (Abbot) on Nov 18, 2017 at 02:11 UTC
Yes, that appears to be what's happening: `C:>perl -le "sub u { unless(shift) { 'false' } }; print u($_) for unde +f, '', 0..3" false false false 1 2 3 C:>perl -le "sub i { if(shift) { 'true' } }; print i($_) for undef, '' +, 0..3" 0 true true true` [download] I'm not sure if it's meeting the technical definition of "expression" from "If no return is found and if the last statement is an expression, its value is returned"... but the last statement executed was the failed `if` or `unless`, and as part of that execution of that statement, the `CONDITIONAL` expression had to be evaluated, so I can definitely see a good case for why that `EXPR`'s value is what is returned. But since I couldn't find a perl-specific definition of "expression" (and it appears it's been a longstanding lack of definition, because as far back as 2001, people were asking What is the difference between a Statement and an Expression? without getting a canonical answer from the perl documents), there is wiggle-room in the interpretation of whether the documents claim the return value is unspecified or not. Interesting sub-discussion. Thanks!	[reply] [d/l] [select]
Re^9: resetting a foreach loop! by AnomalousMonk (Archbishop) on Nov 18, 2017 at 20:26 UTC
Now that I've thought about it some more, I think the point ikegami is making is that just the fact that a behavior is commonly implemented doesn't mean it is actually specified anywhere. And in this case, the behavior of `if (CONDITION) BLOCK` is nowhere specified, so don't rely on it. As I've mentioned before and as you've noted, the behavior of an `if`-statement returning the result of evaluating `CONDITION` when `CONDITION` is false and the `if`-statement is the final statement executed in a subroutine is familiar and seems quite reasonable; it's not surprising that many, perhaps most, Perl implementations adopt this behavior. Whether this behavior is specified and reliable is another question, one I don't have time to pursue ATM. Other questions occur: what's returned from evaluation of a false `CONDITION` in a `while`-loop that is the last statement executed in a subroutine? (I don't dare think about what's going on with a `for`-loop!) Food for thought — and links for more reading. Give a man a fish: `<%-{-{-{-<`	[reply] [d/l] [select]