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Re^2: Compiling Regular Expressions

by johndeighan (Novice)
on Mar 11, 2016 at 16:05 UTC ( #1157455=note: print w/replies, xml ) Need Help??

in reply to Re: Compiling Regular Expressions
in thread Compiling Regular Expressions

I want to embed Perl code in my regex using (?{...}), so it's critical that the regex is compiled at compile time. I've gotten this to work without errors or warnings:

my $kind; my $REGEX = qr/ [A-Za-z][\w]* (?{$kind = 'IDENT';}) | (?: ==? | != | <=? | >=? ) (?{$kind = 'OP';}) | -?\d+ (?{$kind = 'INT';}) | \x27 ( (?:[^\x27] | \x27{2})* ) \x27 (?{$kind = 'STRING';}) | \S (?{$kind = 'OTHER';}) /xs;

However, I'd like to better organize the regex by splitting it into parts, then using those parts. This is what I'd like to do, but when I try, I get the error "Eval-group not allowed at runtime, use re 'eval' in regex". I think that the suggested workaround is bad practice, so I won't do it, but I don't understand why what I'm trying to do won't work since all the regex's involved use qr//. I've also tried using Readonly for the parts, but Perl still doesn't recognize that the parts I'm using will never change. Is there any other way to get $REGEX to compile at compile time while breaking it into parts?

my $IDENT = qr/ [A-Za-z][\w]* /xs; my $STRING = qr/ \x27 ( (?:[^\x27] | \x27{2})* ) \x27 /xs; my $OP = qr/ (?: ==? | != | <=? | >=? ) /xs; my $INT = qr/ -?\d+ /xs; my $kind; my $REGEX = qr/ $IDENT (?{$kind = 'IDENT';}) | $OP (?{$kind = 'OP';}) | $INT (?{$kind = 'INT';}) | $STRING (?{$kind = 'STRING';}) | \S (?{$kind = 'OTHER';}) /xs;

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Re^3: Compiling Regular Expressions
by stevieb (Canon) on Mar 11, 2016 at 17:08 UTC

    You must be using a version of perl that is less than v5.18, as this behaviour works for me on 5.18+, and is documented as such in v5.18 perldelta... search for "The use re 'eval' pragma".

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