divs1210/lisp.html

## lisp.html
<!DOCTYPE html>
<html>
    <head>
        <meta charset="UTF-8">
    </head>

    <body>
        <div>
            <center>
                <h3>Lisp.js</h3>
                <h4>Use the browser console to try it out!</h4>
            </center>

            <pre style="margin-left: 44%;">
let env = baseEnv();
let code = ['+', 1, 2];
lispEval(code, env);
            </pre>
        </div>

        <script type="text/javascript">
         let parentEnvKey = '__parent_env__';

         function getTopLevel(env) {
             if(parentEnvKey in env)
                 return getTopLevel(env[parentEnvKey]);

             return env;
         }

         function lookup(env, symbol) {
             if(symbol in env)
                 return env[symbol];

             if(parentEnvKey in env)
                 return lookup(env[parentEnvKey], symbol);

             throw 'symbol ' +symbol+ ' is not defined!';
         }

         function makeFunction(params, body, env) {
             let fn_internals = {
                 params: params,
                 body: body,
                 env: env
             };

             return function(...args) {
                 return lispApply(fn_internals, args);
             }
         }

         function zipmap(keys, vals) {
             var result = {};

             keys.forEach((key, i) => {
                 result[key] = vals[i];
             });

             return result;
         }

         function lispApply(fn, args) {
             let fnEnv = zipmap(fn.params, args);
             fnEnv[parentEnvKey] = fn.env;

             return lispEval(fn.body, fnEnv);
         }

         function lispEval(exp, env) {
             if(typeof exp == 'number') { // numbers
                 return exp;
             } else if(typeof exp == 'string') { // symbols
                 return lookup(env, exp);
             } else if(Array.isArray(exp)) { // lists
                 let [operator, ...operands] = exp;

                 switch (operator) {
                     case 'do':
                         let ops = operands;
                         let ret = null;

                         for(let op of ops) {
                             ret = lispEval(op, env);
                         }

                         return ret;

                     case 'def':
                         let [symbol, exp] = operands;
                         let topLevelEnv = getTopLevel(env);
                         topLevelEnv[symbol] = lispEval(exp, env);
                         break;

                     case 'if':
                         let [testExp, thenExp, elseExp] = operands;

                         if(lispEval(testExp, env))
                             return lispEval(thenExp, env);

                         return lispEval(elseExp, env);

                     case 'fn':
                         let [params, body] = operands;
                         return makeFunction(params, body, env);

                     case 'quote':
                         let [quoted] = operands;
                         return quoted;

                     case 'js*':
                         let [jsCode] = operands;
                         return eval(jsCode);

                     default:
                         let fn = lispEval(operator, env);
                         let args = operands.map((o) => lispEval(o, env));

                         return fn(...args);
                 }
             }
         }

         function baseEnv() {
             return {
                 '+' : (a, b) => a + b,
                 '-' : (a, b) => a - b,
                 '*' : (a, b) => a * b,
                 '/' : (a, b) => a / b,
                 '^' : (a, b) => Math.pow(a, b),

                 '=' : (a, b) => a === b,
                 '<' : (a, b) => a < b,
                 '>' : (a, b) => a > b,
                 '<=': (a, b) => a <= b,
                 '>=': (a, b) => a >= b,

                 'not': (a) => !a
             };
         }
        </script>
    </body>
</html>
	<!DOCTYPE html>
	<html>
	<head>
	<meta charset="UTF-8">
	</head>

	<body>
	<div>
	<center>
	<h3>Lisp.js</h3>
	<h4>Use the browser console to try it out!</h4>
	</center>

	<pre style="margin-left: 44%;">
	let env = baseEnv();
	let code = ['+', 1, 2];
	lispEval(code, env);
	</pre>
	</div>

	<script type="text/javascript">
	let parentEnvKey = '__parent_env__';

	function getTopLevel(env) {
	if(parentEnvKey in env)
	return getTopLevel(env[parentEnvKey]);

	return env;
	}

	function lookup(env, symbol) {
	if(symbol in env)
	return env[symbol];

	if(parentEnvKey in env)
	return lookup(env[parentEnvKey], symbol);

	throw 'symbol ' +symbol+ ' is not defined!';
	}

	function makeFunction(params, body, env) {
	let fn_internals = {
	params: params,
	body: body,
	env: env
	};

	return function(...args) {
	return lispApply(fn_internals, args);
	}
	}

	function zipmap(keys, vals) {
	var result = {};

	keys.forEach((key, i) => {
	result[key] = vals[i];
	});

	return result;
	}

	function lispApply(fn, args) {
	let fnEnv = zipmap(fn.params, args);
	fnEnv[parentEnvKey] = fn.env;

	return lispEval(fn.body, fnEnv);
	}

	function lispEval(exp, env) {
	if(typeof exp == 'number') { // numbers
	return exp;
	} else if(typeof exp == 'string') { // symbols
	return lookup(env, exp);
	} else if(Array.isArray(exp)) { // lists
	let [operator, ...operands] = exp;

	switch (operator) {
	case 'do':
	let ops = operands;
	let ret = null;

	for(let op of ops) {
	ret = lispEval(op, env);
	}

	return ret;

	case 'def':
	let [symbol, exp] = operands;
	let topLevelEnv = getTopLevel(env);
	topLevelEnv[symbol] = lispEval(exp, env);
	break;

	case 'if':
	let [testExp, thenExp, elseExp] = operands;

	if(lispEval(testExp, env))
	return lispEval(thenExp, env);

	return lispEval(elseExp, env);

	case 'fn':
	let [params, body] = operands;
	return makeFunction(params, body, env);

	case 'quote':
	let [quoted] = operands;
	return quoted;

	case 'js*':
	let [jsCode] = operands;
	return eval(jsCode);

	default:
	let fn = lispEval(operator, env);
	let args = operands.map((o) => lispEval(o, env));

	return fn(...args);
	}
	}
	}

	function baseEnv() {
	return {
	'+' : (a, b) => a + b,
	'-' : (a, b) => a - b,
	'' : (a, b) => a b,
	'/' : (a, b) => a / b,
	'^' : (a, b) => Math.pow(a, b),

	'=' : (a, b) => a === b,
	'<' : (a, b) => a < b,
	'>' : (a, b) => a > b,
	'<=': (a, b) => a <= b,
	'>=': (a, b) => a >= b,

	'not': (a) => !a
	};
	}
	</script>
	</body>
	</html>