empty regular expressions don't work on the BSDs

empty regular expressions don't work on the BSDs

[Andreas Vögele]

There are five tests in test-suite/tests/numbers.test that use an empty 
regular expression. Here's the first test:

    (pass-if-exception
     "Proper exception with 0 modulus"
     (cons 'numerical-overflow "") <-- empty RE
     (modulo-expt 17 23 0))

The problem is that on Mac OS X and the other BSDs regcomp() does not 
accept empty regular expressions. The BSD regex implementation is based 
on Henry Spencer's implementation. I don't know what POSIX says about 
empty REs but Henry Spencer's manual page says that "an empty string is 
not a legal RE" (see http://arglist.com/regex/regex3.html).

The tests in numbers.test succeed if the empty REs are replaced with 
".". Another option would be to handle empty REs in string-match.



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Re: empty regular expressions don't work on the BSDs

[Kevin Ryde]

Andreas Vögele <voegelas@gmx.net> writes:
>
>      (cons 'numerical-overflow "") <-- empty RE

Thanks, I introduced an exception:numerical-overflow doing this
properly, and used exception:wrong-type-arg for the other empties.

> Another option would be to handle empty REs in string-match.

I think it could follow the libc, as long as it doesn't crash.


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Re: empty regular expressions don't work on the BSDs

[Andreas Vögele]

Kevin Ryde writes:

>> Another option would be to handle empty REs in string-match.
>
> I think it could follow the libc, as long as it doesn't crash.

Yes. In practice empty regular expression aren't common anyway.

Henry Spencer's regcomp doesn't crash if the regular expression is  
empty. Instead the error code REG_EMPTY is returned. POSIX doesn't  
define REG_EMPTY but the RE grammar presented in the POSIX  
specification doesn't seem to allow empty REs either. See  
http://www.opengroup.org/onlinepubs/009695399/basedefs/ 
xbd_chap09.html#tag_09_05



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