-This lambda evaluator will allow you to write lambda terms and evaluate (that is, normalize) them, and inspect the results.
-(This won't work in Racket, because Racket doesn't even try to represent the internal structure of a function in a human-readable way.)
-
-*Lambda terms*: lambda terms are written with a backslash, thus: `((\x (\y x)) z)`.
-
-If you click "Normalize", the system will try to produce a normal-form lambda expression that your original term reduces to (~~>). So `((\x (\y x)) z)` reduces to `(\y z)`.
-
-*Let*: in order to make building a more elaborate set of terms easier, it is possible to define values using `let`.
-In this toy system, `let`s should only be used at the beginning of a file. If we have, for intance,
-
- let true = (\x (\y x)) in
- let false = (\x (\y y)) in
- ((true yes) no)
-
-the result is `yes`.
-
-*Comments*: anything following a semicolon to the end of the line is ignored.
-Blank lines are fine.
-
-*Abbreviations*: In an earlier version, you couldn't use abbreviations. `\x y. y x x` had to be written `(\x (\y ((y x) x)))`. We've upgraded the parser though, so now it should be able to understand any lambda term that you can.
-
-*Constants*: The combinators `S`, `K`, `I`, `C`, `B`, `W`, and `T` are pre-defined to their standard values. Also, integers will automatically be converted to Church numerals. (`0` is `\s z. z`, `1` is `\s z. s z`, and so on.)
-
-
-
-<textarea id="INPUT" style="border: 2px solid black; color: black; font-family: monospace; height: 3in; overflow: auto; padding: 0.5em; width: 100%;">
-let true = \x y. x in
-let false = \x y. y in
-let and = \l r. l r false in
-(
- (and true true yes no)
- (and true false yes no)
- (and false true yes no)
- (and false false yes no)
-)
-</textarea>
-<input id="PARSE" value="Normalize" type="button">
-<input id="ETA" type="checkbox">do eta-reductions too
-<noscript><p>You may not see it because you have JavaScript turned off. Uffff!</p></noscript>
-<script src="/code/lambda.js"></script>
-<script src="/code/tokens.js"></script>
-<script src="/code/parse.js"></script>
-<script src="/code/json2.js"></script>
-<pre id="OUTPUT">
-</pre>
-<script>
-/*jslint evil: true */
-
-/*members create, error, message, name, prototype, stringify, toSource,
- toString, write
-*/
-
-/*global JSON, make_parse, parse, source, tree */
-
-// Make a new object that inherits members from an existing object.
-
-if (typeof Object.create !== 'function') {
- Object.create = function (o) {
- function F() {}
- F.prototype = o;
- return new F();
- };
-}
-
-// Transform a token object into an exception object and throw it.
-
-Object.prototype.error = function (message, t) {
- t = t || this;
- t.name = "SyntaxError";
- t.message = message;
- throw t;
-};
-
-
-(function () {
- var parse = make_parse();
-
- function go(source) {
- var string, tree, expr, eta;
- try {
- tree = parse(source);
- // string = JSON.stringify(tree, ['key', 'name', 'message', 'value', 'arity', 'first', 'second', 'third', 'fourth'], 4);
- expr = tree.handler();
- // string = JSON.stringify(expr, ['key', 'name', 'message', 'value', 'arity', 'first', 'second', 'tag', 'variable', 'left', 'right', 'bound', 'body' ], 4);
-// string = expr.to_string() + "\n\n~~>\n\n";
- string = '';
- eta = document.getElementById('ETA').checked;
- string = string + reduce(expr, eta, false).to_string();
- } catch (e) {
- string = JSON.stringify(e, ['name', 'message', 'from', 'to', 'key',
- 'value', 'arity', 'first', 'second', 'third', 'fourth'], 4);
- }
- document.getElementById('OUTPUT').innerHTML = string
- .replace(/&/g, '&')
- .replace(/[<]/g, '<');
- }
-
- document.getElementById('PARSE').onclick = function (e) {
- go(document.getElementById('INPUT').value);
- };
-}());
-
-</script>
-
-
-
-Under the hood
----------------
-
-The interpreter is written in JavaScript and runs inside your browser.
-So if you decide to reduce a term that does not terminate (such as `((\x (x x)) (\x (x x)))`), it will be your
-browser that stops responding, not the wiki server.
-
-The main code is [here](http://lambda.jimpryor.net/code/lambda.js). Suggestions for improvements welcome.
-
-The code is based on:
-
-* Chris Barker's JavaScript lambda calculator
-* [Oleg Kiselyov's Haskell lambda calculator](http://okmij.org/ftp/Computation/lambda-calc.html#lambda-calculator-haskell).
-* The top-down JavaScript lexer and parser at <http://javascript.crockford.com/tdop/index.html>.
-
-Improvements we hope to add soon: the ability to reduce Combinatory Logic combinators and report the result as combinators, rather than in lambda forms.
-
-