var Value = function(){
  var Tuple = function() {
      var len = arguments.length;
      var arr = new Array(len+1);
      arr[0] = "Tuple" + arguments.length;
      for (var i = len; i--; ) {
	  arr[i+1] = arguments[i];
      }
      return arr;
  };

  var toString = function(v) {
    if (typeof v === "boolean") {
	return v ? "True" : "False";
    } else if (typeof v === "number") {
	return v+"";
    } else if (v[0]) {
	if (v[0].substring(0,5) === "Tuple") {
	    var output = "";
	    for (var i = v.length; --i; ) {
		output = "," + toString(v[i]) + output;
	    }
	    if (output[0] === ",") output = output.substring(1);
	    return "("+output+")";
	} else if (v[0] === "Cons") {
	    var start = (typeof v[1] === "string") ? '"' : "[";
	    var  end  = (typeof v[1] === "string") ? '"' : "]";
	    var  div  = (typeof v[1] === "string") ?  "" : ",";
	    var output = start + toString(v[1]);
	    v = v[2];
	    while (true) {
		if (v[0] === "Cons") {
		    output += div + toString(v[1]);
		    v = v[2];
		} else {
		    return output + end;
		}
	    }
	} else if (v[0] === "Nil") {
	    return "[]";
	} else {
	    var output = "";
	    for (var i = v.length; --i; ) {
		output = " " + toString(v[i]) + output
	    }
	    output = v[0] + output;
	    return (v.length > 1) ? "(" + output + ")" : output;
	}
    }
    return v+"";
  };
  var show = function(v) {
      return Text.monospace(String.properEscape(toString(v)));
  };
  var append = function(xs,ys) {
    if (typeof xs === "string" && typeof ys === "string") {
	return xs.concat(ys);
    }
    if (xs[0] === "Nil") {
	return ys;
    }
    var root = ["Cons", xs[1], ["Nil"]];
    var curr = root;
    xs = xs[2];
    while (xs[0]==="Cons") {
	curr[2] = ["Cons", xs[1], ["Nil"]];
	xs = xs[2];
	curr = curr[2];
    }
    curr[2] = ys;
    return root;
  };
  return {show:show, Tuple:Tuple, append:append};
}();