/^(a+)(b+)(c+)$(?(?{length($1) == length($2) && length($2) == length($
+3)})|(*FAIL))/;
But that's just a fancy way of writing:
/^(a+)(b+)(c+)$/ && length($1) == length($2) && length($2) == length($
+3);
And you can solve the "match a square" with:
/^([0-9]+)$(?(?{sqrt($1) == int sqrt($1)})|(*FAIL))/;
Or in general, match "whatever" by:
/^(.*)$(?(?{is_whatever($1)})|(*FAIL))/;
after writing the appropriate "is_whatever" function.
But that means the question no longer is "how can I do foo with a regexp", but "how can I do foo in Perl". |