var t = frequire('Text::Balanced');

func sexpr(txt) {
    txt.trim!;

    var m = txt.match(/^\((.*)\)$/s) || die "Invalid: <<#{txt}>>";
    txt = m[0];

    var w;
    var ret = [];
    while (!txt.is_empty) {
        given (txt.first) {
            when('(') {
                (w, txt) = t.extract_bracketed(txt, '()');
                w = sexpr(w);
            }
            when ('"') {
                (w, txt) = t.extract_delimited(txt, '"')
                w.sub!(/^"(.*)"/, {|s1| s1 });
            }
            default {
                txt.sub!(/^(\S+)/, {|s1| w = s1; '' });
            }
        }
        ret << w;
        txt.trim_beg!;
    }
    return ret;
}

func sexpr2txt(String e) {
    e ~~ /[\s"\(\)]/ ? do { e.gsub!('"', '\\"'); %Q("#{e}") } : e;
}

func sexpr2txt(expr) {
    '(' + expr.map {|e| sexpr2txt(e) }.join(' ') + ')';
}

var s = sexpr(%q{

((data "quoted data" 123 4.5)
 (data (!@# (4.5) "(more" "data)")))

});

say s;              # dump structure
say sexpr2txt(s);   # convert back