Re^3: perl5 vs perl6

let is like temp but it's only useful inside of rules. If the rule succeeds, then the variable keeps the hypothesized value. If the rule fails, then the variable loses its hypothesized value and thus reverts back to whatever value it had before (if any).

This is all as far as I know anyway. But then, things I thought I knew about rules have changed at least 2 times since I learned them, so who really knows anyway? ;-)

duff

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Re^4: perl5 vs perl6 by blazar (Canon) on Jan 09, 2005 at 14:07 UTC
let is like temp but it's only useful inside of rules. If the rule succeeds, then the variable keeps the hypothesized value. If the rule fails, then the variable loses its hypothesized value and thus reverts back to whatever value it had before (if any). I've quickly searched around and indeed it seems to be so. That is, `let` is to be used in closures embedded in rules. Due to the deep analogy between rules and subs I wonder wether the same mechanism could be made to work also for the latter ones (using the return value for success): I do not see any immediate use, but I bet someone could find one. Well, however this is probably not best discussed here...	[reply] [d/l]
Re^5: perl5 vs perl6 by TimToady (Parson) on Jan 10, 2005 at 18:42 UTC
Sigh. A `let` may certainly be used in ordinary blocks. See http://dev.perl.org/perl6/synopsis/S04.html for the definition of successful exit. The `KEEP` and `UNDO` blocks use the same definition, and are arguably part of the same underlying mechanism. You can view a `let` as a `temp` that merely does `UNDO` instead of `LEAVE`.	[reply] [d/l] [select]
Re^6: perl5 vs perl6 by blazar (Canon) on Jan 11, 2005 at 09:56 UTC
Sigh. A let may certainly be used in ordinary blocks. See Sigh. So it is indeed just like I remembered in the first place, which is good news anyway, as I consider this to be a very desirable feature...	[reply]


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