comment on

Though running this program, v1.pl:

                                 (
                     (       (
                           (         (
                (    (         (            (
                                       (
             (      (       (    (          (    (
                             ''
                )      )      )))   )    )     )   )
           )                  )))))
                  )          =~("\(".           (
                       (    '?')).'{'   .    (
                (           '`')|'%')
                             .('['^  (   '-')
                      )    .    (     '`'|'!')
                                .  ('`'|"\,").
                             '"'.('['^"\+").(
                        '['^')').('`'|(')')).(
                    '`'|'.').('['^'/').(('{')^
                    '[').'\\'.'"'.('`'|"\(").(
                    '`'|'%').('`'|',').("\`"|
                    ',').('`'|'/').('{'^'[').
                    ('['^',').('`'|'/').("\["^
                   ')').('`'|',').('`'|('$')).
                  '\\'.'\\'.('`'|'.').'\\'.'"'
                  .';'.('!'^'+').'"'.'}'.')');
[download]

works fine with perl 5.16, running it with perl 5.17.10 produces an error:

Eval-group not allowed at runtime, use re 'eval' in regex m/(?{eval"pr
+int\"hello world\\n\";
"})/ at v1.pl line 25.
[download]

Note that the Acme::EyeDrops-generated string being eval'ed above is a constant expression, as can be seen by running:

perl -MO=Deparse v1.pl
[download]

which produces:

'' =~ /(?{eval"print \"hello world\\n\";\n"})/;
v1.pl syntax OK
[download]

Note further that running the deparsed program above works fine in perl 5.17 without requiring a leading use re 'eval'.

Though v1.pl can be made to work with perl 5.17.10 by adding a leading:

use re 'eval';
[download]

this destroys the artistic effect of having no alphanumeric characters at all. :) Moreover, I wonder why this is necessary, given the string being eval'ed is a constant expression and given that the deparsed program does not require it.

This change in use re 'eval' behavior was presumably introduced by Dave Mitchell's "re_eval jumbo fix" (see also ticket #113682). Given my test program above does not use tieing or overloading and no variables are interpolated in the (constant) expression, I wonder if this is a Perl 5.17 bug -- or am I missing something?

Assuming that use re 'eval' is really required for Perl v5.17.1+, I will need to fix the Acme::EyeDrops test suite to pass with the upcoming perl 5.18. Though adding a leading:

use if $] >= 5.017, re => 'eval';
[download]

or:

use if $^V && $^V gt 5.17.0, re => 'eval';
[download]

both seem to work fine, which is preferred?

References

Conditionally executing different code based on Perl Version
Version numbers should be boring (dagolden blog)
version
perlvar (see $] and $^V)
perldata (see "Version Strings" section)

In reply to Perl 5.17 change to use re 'eval' breaks Acme::EyeDrops by eyepopslikeamosquito

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