*Constants*: The combinators `S`, `K`, `I`, `C`, `B`, `W`, `T`, `M` (aka <code>ω</code>) and `L` 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.)
+*Variables*: Variables must start with a letter and can continue with any sequence of letters, numbers, `_`, `-`, or `/`. They may optionally end with `?` or `!`. When the evaluator does alpha-conversion, it may change `x` into `x'` or `x''` and so on. But you should not attempt to use primed variable names yourself.
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* [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.
+Improvements we hope to add:
+* detecting some common cases of non-normalizing terms (the problem of determining in general whether a term will normalize is undecidable)
+* returning results in combinator form (the evaluator already accepts combinators as input)
+* displaying reductions one step at a time
+* specifying the reduction order and depth
+* allow other binders such as ∀ and ∃ (though these won't be interpreted as doing anything other than binding variables)
+
+<a name="other_evaluators"></a>
+Other Lambda Evaluators/Calculutors
+-----------------------------------
+
+* [Peter Sestoft's Lambda Calculus Reducer](http://www.itu.dk/people/sestoft/lamreduce/index.html): Very nice! Allows you to select different evaluation strategies, and shows stepwise reductions.
+* [Chris Barker's Lambda Tutorial](http://homepages.nyu.edu/~cb125/Lambda)
+* [Penn Lambda Calculator](http://www.ling.upenn.edu/lambda/): Pedagogical software developed by Lucas Champollion, Josh Tauberer and Maribel Romero. Linguistically oriented. Requires installing Java (Mac users will probably already have it installed).
+* [Mike Thyer's Lambda Animator](http://thyer.name/lambda-animator/): Graphical tool for experimenting with different reduction strategies. Also requires installing Java, and Graphviz.
+* [Matt Might's Lambda Evaluator](http://matt.might.net/articles/implementing-a-programming-language/) in Scheme (R5RS and Racket).
+
+See also:
+
+* [Jason Jorendorff's Try Scheme](http://tryscheme.sourceforge.net/about.html): Runs a miniature Scheme interpreter in Javascript, in your browser.