Re^2: Compiling Regular Expressions

[johndeighan]

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;

[stevieb]

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".