From: Dan Zwell <dzwell@...>
Date: 2007-08-29T08:16:12+09:00
Subject: Re: gsub help

hurcan solter wrote:
>   Hi there;
>   this is more of a regexp question but I'de be happy if you help me
> since i am doing it in ruby.
>   i want to beautify some line by inserting or removing some space
> around the operators like = or ==
>  so i came up with an expression like;
> 
>   line.gsub!(/\s*([=]+)\s*/ ,' \1 ')
> 
> But it applies every = on the line ofc, but I want to exclude
> expressions between quotation marks ("sth=sth") or regexp (/sth=sth/).
> I've tried negated character classes and such to no avail.How can I do
> this?
>  Any help would be greatly appreciated...
>  Hurcan
> 
> 
> 

Hurcan,
That's a very hard problem. If you think creatively, you can probably 
come up with a decent algorithm, and then a handful of examples that 
break it. For each "=" or "==", you need to decide whether it is between 
a pair of unescaped slashes, quotes, or other form of quoting (like %Q|| 
or %x{}). I doubt there is any way to do this with a regexp. You need to 
write some code that makes decisions about whether any of the following 
symbols has semantic meaning:
|\{}@^#()     and any other that can be used in the % quoting construct

Once you determine which ones have meaning (and which are escaped, or 
insignificant in their current context), you can decide whether some "=" 
should be re-spaced, based on its position relative to these characters. 
The more I think about it, the more I think you can't do this without 
writing a ruby parser.

puts ("this problem is nontrivial"    ==    true)
puts %q("this problem is nontrivial"  ==    true)
puts %q("this problem is nontrivial", says a

string  ==    true)

Good luck,
Dan