Regular expression - replacement inner to outer

Question

So I am building a parser for stylesheets. And in my CSS file, I will parse something like this:

body {
   background-image: &gradient(#1073b8, &saturate(#1073b8, -20), 40);
}

The result would be a value of something like this:

body {
   background-image: url(/cache/graident12345.png);
}

Which is the output of my &gradient() function, that I catch and execute. But one of the arguments to &gradient() is the result of &saturate() , so it's hierarchical, and I need preg_replace() to handle them inner to outer, but how do I do that? So first catch and parse &saturate() , return a color HEX value, which in turn will be in the string when parsing &gradient() . My current lookup code looks like this:

if (preg_match("/\&(gradient|saturate)\((.*?)\)/", $value, $m)){
   $arg = explode(", ", $m[2]); # splits argument to the function
   if ($m[1] == "saturate"){
       $value = str_replace($m[0], saturate($arg[1], $arg[2]);
   }
}

And I'll add functions as I make them available. Alternatively, catch the function name as well in the regexp.

Do I make myself clear? Any ideas? :)

Answer 1

You can do some interesting parsing using regex in combination with a recursive function. I have mocked up something that will work for your scenario, feel free to tweak it to your needs.

http://ideone.com/66tV0

If you need any explanation of what is going on, let me know, but it basically creates a recursive structure through a recursive call to a function that regexes for the pattern &functionname([args...]) .