Difference between //, m//, and rx// in regex

[trosel]

hankache/rakuguide#135

What might be a good/quick way to explain the differences in the intro guide?

[raiph]

• / ... / declares a regex. If it's used in sink context or on the right of ~~ it is also run.

• rx/ ... / is the same as / ... / except that rx can use alternative delimiters, eg. rx { ... }.

• m/ ... / is the same as rx/ ... / except that it is always immediately run.

[tisonkun]

FWIW, users may be curious about why m:g works but rx:g doesn't. We can point it out explicitly.

[12:55] <raiph> wander: yes. some adverbs apply *inside* the *declarations* of regexes, others apply to *matches* see https://docs.perl6.org/language/regexes#Matching_adverbs
[12:58] <wander> how about the difference between 'rx:g' and 'm:g'
[13:03] <raiph> m is a match operation that can take match adverbs; it just happens to include a regex declaration in its syntax
[13:04] <raiph> rx is a regex declaration that can't take match adverbs; it just happens to sometimes be immediately run if in sink context or rhs of ~~

https://github.com/rakudo/rakudo/blob/fff43fd709cd0ed9693a85d06242f0fcd9f55ba3/src/Perl6/Grammar.nqp#L3814-L3833

https://github.com/rakudo/rakudo/blob/fff43fd709cd0ed9693a85d06242f0fcd9f55ba3/src/Perl6/Actions.nqp#L8056-L8088

[trosel]

@raiph is your explanation in the docs? I couldn't find it by searching m// or rx//

I think I must have found it previously in a regex guide separate from the search bar.

[raiph]

@WildYorkies Searching for rx leads to the general language/regex page which explains this stuff starting at the section Adverbs.

Edited to add...

Er, I thought you were asking about the adverb explanation.

If you mean my three bullet point summary, that's just my own best effort at an accurate and comprehensive explanation, hopefully brief and simple enough for the intro, but maybe not, explaining the differences between the three constructs listed in this issue's title. I think that what I've written is implicit in a careful reading of the longer more scattered explanations in the doc but ymmv.

[AlexDaniel]

I'm a bit late to the party, but FWIW here are some tickets:

• RT#130363 [open]: [@LARRY] there's no match for Any aka /./ codegens differently from m/./
• RT#131925 [open]: [BUG] [REGEX] Smartmatch against `m//` operator mishandles junctions

[zoffixznet]

/ ... / declares a regex. If it's used in sink context or on the right of ~~ it is also run.

Also in Bool context.

[tisonkun]

Close this via 6dec94a
https://docs.perl6.org/language/regexes#Lexical_Conventions