At the top of http://deps.cpantesters.org/ there is a link titled "Reverse lookup". It leads to http://deps.cpantesters.org/depended-on-by.pl, which I would imagine implements http://deps.cpantesters.org/ but in reverse.

Also, I'm under the impression that the problem of Regex::Grammars with 5.18 is reliance of a bug in Perl which was fixed. This then uncovered segfaults in the regex engine, which should be fixed in 5.18.1. There seems to be some discussion on p5p regarding this:

In reply to Re: Which modules on the whole CPAN depends on this module? by Corion
in thread Which modules on the whole CPAN depends on this module? by sedusedan

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