Any time there's a bug report based on a serious misunderstanding of language behaviour by someone otherwise apparently competent, should it be considered an LTA for the relevant part of the documentation?
On 1/15/17, jn...@jnthn.net via RT <perl6-bugs-follo...@perl.org> wrote: > On Sun, 15 Jan 2017 05:06:21 -0800, ronaldxs wrote: >> So "42" ~~ / [ "0" || "42" ] | "4" / matches 4 but if you stick to just >> one kind of alternation: >> >> "42" ~~ / [ "0" | "42" ] | "4" / >> >> "42" ~~ / [ "0" || "42" ] || "4" / >> >> the match correctly comes back with 42. It looks like in the mixed case >> the "|" longest alternation is not picking the longest match which is a >> bug. >> > This is not a bug. `||` is by design not declarative, and so only the first > branch of it is significant for LTM purposes. This behavior can be confirmed > by re-ordering the imperative alternation: > >> "42" ~~ / [ "0" || "42" ] | "4" / > ｢4｣ >> "42" ~~ / [ "42" || "0" ] | "4" / > ｢42｣ > > Therefore, the longest declarative match is 4, and so that is the branch > that LTM selects. Since there's no anchoring, there's furthermore no reason > for it to backtrack into the second branch of the `|` to try the other `||` > branch. > > I'm pretty sure this behavior is relied upon in the Perl 6 grammar itself; > off the top of my head, it shows up in a bunch of places for the sake of > error handling. > > So, working as designed. > > Thanks, > > /jnthn >
