OPTIONAL
SYNOPSIS
        string process_string(string str)

DESCRIPTION
        Searches string str for occurences of a "value by function
        call", which is @@ followed by an implicit function call. See
        "value_by_function_call" in the principles section.

        The value should contain a string like this:
        @@function[:filename][|arg|arg]@@

        function must return a string or else the string which should be
        processed will be returned unchanged.

        Note that process_string() does not recurse over returned
        replacement values. If a function returns another function
        description, that description will not be replaced.

        Note that both filename and args are optional.

EXAMPLE
        string foo(string str) {
           return "ab"+str+"ef";
        }
        void func() {
           write(process_string("@@foo|cd@@")+"\n");
        }

        The function func() will print out the string "abcdef".

BUGS
        Using process_string() can lead to severe security problems.

HISTORY
        Because of the security problems, process_string() is an
        optional efun since 3.2.1@34

SEE ALSO
        notify_fail(E), closures(LPC), get_bb_uid(M)