Perl6 getting a regex from a string

Question

I want to put a regex in a YAML config file (say: config/filename.yaml), eg.

-
  section: Begining
  regex: '/ ^ <[ a..b, A..B ]> /'
-
  section: Next
  regex: '/ ^ <[ c..z, C..Z ]> /'

When I read this into a hash (eg. using YAMLish), eg.,

use YAMLish;
my @h = load-yaml('config/filename.yaml'.IO.slurp);

naturally I have a string in @h[0]<regex>

So how do I recover a regex from a string for use in a match?

I want something like the following, but the following doesn't work:

say 'Its a beginning' if 'A beginning' ~~ @h[0]<regex>

It doesn't work as desired because @h[0]<regex> is a Str, so the smart match is testing a Str in @h[0]<regex> against a Str literal. So how to get the regex out of the Str?

Christoph · Accepted Answer · 2018-11-24 14:52:19Z

12

You interpolate a string held in a variable $var into a regex via / <$var> /, or, in case of more complex expressions like yours, / <{ @h[0]<regex> }> /.

Note, however, that you first have to remove the enclosing slashes from your string. For trusted input, there's of course always EVAL...

answered Nov 24, 2018 at 14:52

Christoph

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Comments

nxadm · Accepted Answer · 2018-12-09 11:46:57Z

1

I think it's a good idea to compile external regexes, so you know right away if they fail (and they will be faster afterwards):

Perl6 REPL:

> my $str = '\d+'; my $rx = rx/ <$str> /; say "a" ~~ $rx; say "10" ~~ $rx
Nil
｢10｣

Of course it's easier providing a "pure" regex, not one that also has syntax (/ /).

Perl documentation

edited Dec 9, 2018 at 11:46

answered Dec 9, 2018 at 11:38

nxadm

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