I need a regular expression to validate regular expressions.  Just
compiling it as a regex in Java and seeing if an
InvalidPatternException is thrown is not acceptable.  It must be a
regex string that matches or doesn't match a string that is a regular
expression

Thanks!

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Request for Question Clarification by endo-ga on 02 Jun 2003 10:44 PDT

What language do you want this in?
Would Haskell be acceptable?
What operators do you want to use?
Thanks.
endo

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Clarification of Question by ksclarke-ga on 02 Jun 2003 11:45 PDT

I do not want code in any particular language but a generic regex
pattern that could be fed to any Perl style regex engine (implemented
in Perl or Java or anything else) that would allow the engine to
validate a supplied regex string (that could be any variation of a
regular expression)...

Basically all standard operators: Match-self Operator,
Match-any-character Operators, Concatenation Operators, Juxtaposition,
Repetition Operators, Alternation Operators, List Operators, Grouping
Operators, Back-reference Operators, Anchoring Operators...

  I'm hoping someone knows where such a thing already exists (it must,
but I haven't been able to find it) since I think actually writing it
is probably more than a ten dollar answer :-)

Thanks

Hello Ksclarke,

I believe it is impossible to produce a "regular expression" for
regular expressions. The problem I see is basically the presence /
absence of nested (), [], and similar constructs. You can certainly
produce a pattern that addresses a "relatively small" set of
combinations, but will fail with anything more complicated. There are
some sites that describe the regular expression problem in numeric
terms such as "NP Complete" and that some patterns require Exponential
processing (not polynomial). I can provide references for them if you
are interested.

  --Maniac