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[lambda.git] / lambda_evaluator.mdwn

diff --git a/lambda_evaluator.mdwn b/lambda_evaluator.mdwn
index 16eace7..ffe1c9d 100644 (file)
--- a/lambda_evaluator.mdwn
+++ b/lambda_evaluator.mdwn
@@ -8,15 +8,30 @@ It will allow you to write lambda terms and evaluate them, with full ability to
 *Lambda terms*: lambda terms are written with a backslash, thus: `((\x (\y x)) z)`.  
 If you click "Reduce", the system will produce a lambda term that is guaranteed to be reduction equivalent (`<~~>`) with the original term.  So `((\x (\y x)) z)` reduces to (a lambda term equivalent to) `(\y z)`.
 
 *Lambda terms*: lambda terms are written with a backslash, thus: `((\x (\y x)) z)`.  
 If you click "Reduce", the system will produce a lambda term that is guaranteed to be reduction equivalent (`<~~>`) with the original term.  So `((\x (\y x)) z)` reduces to (a lambda term equivalent to) `(\y z)`.
 

-*Let*: in order to make building a more elaborate system easier, it is possible to define values using `let`.
+*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
 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 true) false)
+    ((true yes) no)

 
 

-the result is `true`.
+the result is `yes`.  Things to watch out for: the expression after the equal sign must have balanced parentheses,
+and the "in" is obligatory.  If you violate these rules, the system will still produce a result, but it won't make much sense.
+
+*Abbreviations*: No abbreviations work.  So `\xy.yxx` must be written `(\x (\y ((y x) x)))`.  (As in Scheme or Racket.)
+
+*Comments*: anything following a semicolon to the end of the line is ignored.
+Blank lines are fine.
+
+Under the hood
+---------------
+
+The interpreter is written in JavaScript (which is not closely related to Java), 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.
+
+You can inspect the code [here](http://lambda.jimpryor.net/code/lambda.js).  Suggestions for improvements welcome.
+
+Improvements we hope to add soon: the ability to reduce Combinatory Logic combinators; the ability to translate from CL to the lambda calculus; and more sensible variable names instead of `g354`.

 
 

-*Comments*:

 
 

-[more soon]