Case insensitive string_replace()

/*
Case insensitive string_replace() script

Creator: Big J

Date: 02/09/2008

Description: Replaces one or all occurrences of a sub string within a string

Arg 0: String
Arg 1: Sub String
Arg 2: New String to replace Sub String with
Arg 3: Whether to replace ALL occurrences
*/
var str, substr, newstr, pos, str2, substr2, replace_all, len, temp;
str = argument0;
substr = argument1;
newstr = argument2;
replace_all = argument3;
str2 = string_lower(str);
substr2 = string_lower(substr);

while (true)
{
    len = string_length(substr);
    pos = string_pos(substr2, str2);
    if (pos)
    {
        temp = string_copy(str, pos, len);
        str = string_replace(str, temp, newstr);
        str2 = string_replace(str2, substr2, newstr);
    }
    else
        break;
    if (!replace_all)
        break;
}
return str;