Re: bug in elisp... or in elisper???

[ken <gebser@mousecar.com>]

Anything is easy if you know how to do it.


On 03/23/2011 03:01 AM Tim X wrote:
> ken <gebser@mousecar.com> writes:
> 
>> Fellow elispers,
>>
>> Something seems to be amiss in the search syntax here:
>>
>>  (setq aname-re-str
>> "<a\\([\s-\\|\n]+?\\)name=\"\\(.*?\\)\"\\([\s-\\|\n]*?\\)>\\(\\(.\\|\n\\)*?\\)</a\\(\\(
>> \\|\t\\|\n\\)*?\\)>" )
>>
>> ;;Here's a function to use the above RE and return diagnostics:
>>
>> (defun test-aname-search ()
>>   (interactive)
>>   (re-search-forward aname-re-str)
>>   (message "1: \"%s\" 2: \"%s\" 3: \"%s\" 4: \"%s\" 5: \"%s\" 6: \"%s\"
>> 7: \"%s\" 8: \"%s\""
>> 	   (match-string 1)
>> 	   (match-string 2)
>> 	   (match-string 3)
>> 	   (match-string 4)
>> 	   (match-string 5)
>> 	   (match-string 6)
>> 	   (match-string 7)
>> 	   (match-string 8)))
>>
>>
>> Here are some strings to search on:
>>
>> <h3><a name="thisname">Any Text--
>> Hot Stuff</a></h3>
>>
>> <h1
>> class="title"
>>> <a
>> name="heres-a-name"
>> the</a
>>> </h1
>>>
>> <h3><a name="duplicate">Any Text--
>> Hot Crud</a></h3>
>>
>>
>> The problem is that the 5th match-string should be either empty or
>> whitespace.  But it consistently contains the last character of of the
>> 4th match-string.  And these two matches are separated by the literal
>> character string, "</a"!!  What's up with this?
>>
>>
>> Wishing I hadn't quit beer,
>> ken
> 
> I don't think your re is matching what you think it is. Strong recommend
> you try using re-builder as this will give you a visual representation
> of what your re is matching (with different colours representing the
> various match groups).
> 
> Tim

Well, I was missing a crucial bit of knowledge about REs (explained in
two previous posts here) and that was causing me to misinterpret
results.  PJ's reply pointed me in the direction I needed to go to
figure out what the problem was.  And I think it was a mistake for me to
post such a complex example, but I couldn't think of how else to do it.

I read mention of re-builder, but must admit I haven't tried it yet.
With your recommendation, I'm sure I'll be giving it a try on some
future RE puzzle.  The mere fact that this tool exists is comforting...
tells me that I'm not the only one who's occasionally perplexed by REs.

Thanks for the suggestion.