Sometimes I have a long list and I would like to check whether a string matches anything in the list. I am trying to interpolate a junction inside a regex. They are all errors.
say "12345" ~~ m/ <{ (2,3,4).any }> /
Cannot resolve caller MAKE_REGEX(Int, Bool, Bool, Int, PseudoStash); none of these signatures match:
say "12345" ~~ m/ $( (2,3,4).any ) /
This type cannot unbox to a native string: P6opaque, Junction
Does this error message mean that junctions cannot be used inside regex interpolation?
The work-around I have is
say "12345" ~~ m/ <{ (2,3,4).join("||") }> /
｢2｣
How can I use junctions inside regex interpolation?
Sometimes I have a long list and I would like to check whether a string matches anything in the list.
Use a list, not a Junction:
my @list = <bar bartoo baragain>;
say 'bartoo' ~~ / @list /; # ｢bartoo｣
say 'bartoo' ~~ / <{<bar bartoo baragain>}> /; # ｢bartoo｣
Note that by default you get the longest matching token.
I am trying to interpolate a junction inside a regex. They are all errors. ... Does this error message mean that junctions cannot be used inside regex interpolation?
I think so. (The error message is perhaps LTA.) Junctions are a feature of the main P6 language. It seems reasonable that the pattern matching DSL doesn't support them.
The work-around I have is
say "12345" ~~ m/ <{ (2,3,4).join("||") }> /
｢2｣
If you join with a doubled pipe (||) then you get the first token that matches rather than the longest:
say 'bartoo' ~~ / <{'bar || bartoo || baragain'}> /; # ｢bar｣
say 'bartoo' ~~ / ||@list /; # ｢bar｣
say 'bartoo' ~~ / ||<{<bar bartoo baragain>}> /; # ｢bar｣
Not specifying the pipe symbol for these constructs is the same as specifying a single pipe symbol (|) and matches the longest matching token:
say 'bartoo' ~~ / <{'bar | bartoo | baragain'}> /; # ｢bartoo｣
say 'bartoo' ~~ / |@list /; # ｢bartoo｣
say 'bartoo' ~~ / |<{<bar bartoo baragain>}> /; # ｢bartoo｣
You've asked related questions before. I'll add links to a couple of them here for convenience: