X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=week1.mdwn;h=c9b52d1d52acead984f8a6149cdb62db2a39c111;hp=5ae3e65f5c154f36a84432585178ed81bdb179ba;hb=fceb99fda0c4287f9f3c476a26c6e202cf5e26c5;hpb=9452f39dcc5b7babde45142e2b24e3617813d6a6 diff --git a/week1.mdwn b/week1.mdwn index 5ae3e65f..c9b52d1d 100644 --- a/week1.mdwn +++ b/week1.mdwn @@ -39,18 +39,29 @@ Basics of Lambda Calculus The lambda calculus we'll be focusing on for the first part of the course has no types. (Some prefer to say it instead has a single type---but if you say that, you have to say that functions from this type to this type also belong to this type. Which is weird.) +Here is its syntax: + +
+Variables:+ +Each variable is an expression. For any expressions M and N and variable a, the following are also expressions: + +x
,y
,z
... +
+Abstract: (λa M)
+
+
+We'll tend to write (λa M)
as just `(\a M)`, so we don't have to write out the markup code for the λ
. You can yourself write (λa M)
or `(\a M)` or `(lambda a M)`.
+
+
+Application: (M N)
+
+
Some authors reserve the term "term" for just variables and abstracts. We'll probably just say "term" and "expression" indiscriminately for expressions of any of these three forms.
Examples of expressions:
x
- (y x)
- (x x)
- (\x y)
- (\x x)
- (\x (\y x))
- (x (\x x))
- ((\x (x x)) (\x (x x)))
The lambda calculus has an associated proof theory. For now, we can regard the
proof theory as having just one rule, called the rule of **beta-reduction** or