1
Thanks
Expand|Select|Wrap|Line Numbers
- <html>
- <head>
- <script type="text/javascript" src="http://ajax.googleapis.com/ajax/libs/jquery/1.3.2/jquery.min.js"></script>
- <script type="text/javascript">
- var DEBUG = 1;
- var TEST = [
- "(cons 1 nil)",
- "(+ 1 2 (* 3 4))"
- ][0]
- var _text = null;
- var _balanced = 0;
- var _env = null;
- var b = 0;
- function init()
- {
- //(defun fact (x) (if (<= x 1) 1 (* x (fact (- x 1))))) (fact 3)
- document.getElementById("demo").innerHTML= read("(defun fact (x) (if (<= x 1) 1 (* x (fact (- x 1))))) (fact 3)");
- }
- function read(text)
- {
- try
- {
- _balanced = 0;
- _text = $.trim(text);
- var code = ["list"];
- while (_text.length)
- {
- var s = parser();
- //alert(s.length)
- code = code.concat(s);
- //alert(code)
- }
- if (_balanced > 0)
- throw "The expression is not balanced. Add "+_balanced+" parentheses.";
- else if (_balanced < 0)
- throw "The expression is not balanced. Remove "+_balanced+" parentheses.";
- // trace(code);
- if (!_env) _env = {};
- return (eval_(code, _env)).pop();
- }
- catch (e)
- {
- return "Error: "+e;
- }
- }
- function eval_(expr, env)
- {
- //alert(b+": "+expr+" : env: "+env);
- // atoms
- b +=1
- if (!isNaN(expr))
- {
- return Number(expr);
- }
- else if (expr == "nil")
- {
- return null;
- }
- else if (expr[0] == '"')
- {
- return expr.slice(1);
- // list
- }
- else if (expr[0] == "list")
- {
- return $.map(expr.slice(1),
- function(x)
- {
- //alert(x)
- var v = eval_(x, env);
- if ($.isArray(v))
- return Array(v);
- return v;
- });
- // variables
- }
- else if (getenv(expr, env))
- {
- return getenv(expr, env);
- }
- else if (expr[0] == "setq" || expr[0] == "set!")
- {
- env[expr[1]] = eval_(expr[2], env);
- return env[expr[1]];
- // conditional
- }
- else if (expr[0] == "if")
- {
- if (eval_(expr[1], env))
- return eval_(expr[2], env);
- $.each(expr.slice(2, expr[expr.length - 2]),
- function(i, x) { eval_(x, env); });
- return eval_(expr[expr.length - 1], env);
- // procedures
- }
- else if (expr in operators)
- {
- var z = operators[expr];
- return z; //operators[expr];
- }
- else if (expr[0] == "lambda")
- {
- return makeproc(expr[1], expr.slice(2), env);
- }
- else if (expr[0] == "defun")
- {
- alert(expr)
- env[expr[1]] = makeproc(expr[2], expr.slice(3), env);
- return env[expr[1]];
- }
- else if (expr[0] == "js")
- {
- // call a javascript function
- return eval(expr[1]);
- // apply
- }
- else if ($.isArray(expr))
- {
- return apply_(
- eval_(expr[0], env),
- $.map(expr.slice(1), function(x, i)
- {
- var v = eval_(x, env);
- if ($.isArray(v))
- return Array(v);
- return v;
- })
- );
- // error
- }
- else
- {
- throw expr+" is not defined"
- }
- }
- function apply_(proc, args)
- {
- if ($.isFunction(proc)) {
- return proc.apply(this, args);
- }
- throw "Procedure "+proc+" is not defined";
- }
- function makeproc(args, body, env) {
- return function() {
- // extend the env
- //alert(arguments)
- var arguments_ = arguments;
- var newenv = {};
- newenv["__up__"] = env;
- $.each(args, function(i, x) { newenv[x] = arguments_[i]; });
- $.each(body.slice(0, body.length - 1),
- function(i, x) { eval_(x, newenv); });
- return eval_(body[body.length - 1], newenv);
- };
- }
- function getenv(expr, env)
- {
- if (typeof expr != "string") return false;
- if (expr in env) return env[expr];
- if ("__up__" in env) return getenv(expr, env["__up__"]);
- return false;
- };
- ////////////////
- // primitives //
- ////////////////
- var operators = {
- // list
- "car":function() {
- var l = arguments[0];
- if (!l || !l.length) return null;
- return l[0];
- },
- "cdr":function() {
- var l = arguments[0];
- if (!l || !l.length) return [];
- return l.slice(1);
- },
- "cons":function() {
- var a = arguments[1];
- if (a == null) return [arguments[0]];
- a.unshift(arguments[0])
- return a;
- },
- // logical
- "not":function() {
- return !arguments[0];
- },
- "and":function() {
- for (var i = 0; i < arguments.length; i++) {
- if (!arguments[i]) return false;
- }
- return true;
- },
- "or":function() {
- for (var i = 0; i < arguments.length; i++) {
- if (arguments[i]) return true;
- }
- return false;
- },
- // comparison
- "<=":function(x, y) { return x <= y; },
- "<":function(x, y) { return x < y; },
- ">=":function(x, y) { return x >= y; },
- ">":function(x, y) { return x > y; },
- "=":function(x, y) { return x == y; },
- "eq":function(x, y) { return x === y; },
- // arithmetic
- "+":function() {
- var res = 0;
- $.each(arguments, function(i, x) { res += x; });
- return res;
- },
- "-":function() {
- var res = arguments[0] * 2;
- $.each(arguments, function(i, x) { res -= x; });
- return res;
- },
- "*":function() {
- var res = 1;
- $.each(arguments, function(i, x) { res *= x; });
- return res;
- },
- "/":function() {
- var res = arguments[0] * arguments[0];
- $.each(arguments, function(i, x) { res /= x; });
- return res;
- }
- };
- ///////////////////////////
- // convert text to lists //
- ///////////////////////////
- function scanner()
- {
- if (!_text.length) return "";
- var start = 0, index = 1;
- if (_text.charAt(0) == "(" || _text.charAt(0) == ")")
- {
- index = 1;
- // check the text is balanced
- _balanced += _text.charAt(0) == "(" ? 1 : -1;
- }
- else if (_text.charAt(0) == '"')
- {
- index = _text.search(/[^\\]"/) + 1;
- }
- else
- {
- index = _text.search(/[ \n)]/);
- }
- //alert(index)
- if (index < 1) index = _text.length;
- var t = _text.substring(start, index);
- _text = $.trim(_text.substring(index));
- return t;
- }
- function parser()
- {
- var result = [];
- var token = scanner();
- while (token != ")" && token != "")
- {
- var expr = null;
- if (token == "(")
- expr = parser();
- else
- expr = token;
- result.push(expr);
- token = scanner();
- }
- return result;
- }
- </script>
- </head>
- <body>
- <h1>My First Web Page</h1>
- <p id="demo">This is a paragraph.</p>
- <button type="button" onclick="init()">Display Date</button>
- </body>
- </html>
