if(/\G((?i:[a-z]\w*))\s*\(/gc) {  # function '('
        my $function = $1;
        $function{$function} or die sprintf "Undefined function '$function' called at: \"%s\"", where();
        my @arg;
        unless(/\G\s*(?=\))/gc) {
            while(1){
                my($value) = parse_expr() or die sprintf "Expression expected at: \"%s\"", where();
                push @arg, $value;
                /\G\s*,/gc or last;
            }
        }
        /\G\s+/gc;
        /\G\)/gc or die sprintf "Parse error: ')' expected at: \"%s\"", where();
        trace(sprintf "function '$function' called with %d argument%s", scalar @arg, @arg==1 ? "" : "s");
        return $function{$function}->(@arg);
    }