update arith1.ml

[lambda.git] / code / untyped_evaluator.ml

diff --git a/code/untyped_evaluator.ml b/code/untyped_evaluator.ml
index 50092fb..5ccecb5 100644 (file)
--- a/code/untyped_evaluator.ml
+++ b/code/untyped_evaluator.ml
@@ -1,5 +1,5 @@
 (*
-   This is a simplified version of the code at ...
+   This is a simplified version of the code at http://lambda.jimpryor.net/code/untyped_full-1.7.tgz
    You can use this code as follows:
 
    1. First, use a text editor to fill in the (* COMPLETE THIS *) portions.
@@ -15,7 +15,7 @@
       `reduce (App(Lambda("x",Var "x"),Lambda("y",Var "y")))`
       `evaluate (App(Lambda("x",Var "x"),Lambda("y",Var "y")))`
 
-   The two interpreters presented below are (VersionA) a substitute-and-replace
+   The two interpreters presented below are (VersionA) a substitute-and-repeat
    interpreter, and (VersionB) an environment-based interpreter. We discuss the
    differences between these in the course notes.
 
@@ -61,7 +61,7 @@ and env = (identifier * term) list
 (* Operations for environments *)
 let empty = []
 let shift (ident : identifier) binding env = (ident,binding) :: env
-let rec lookup (sought_ident : ident) (env : env) : term option =
+let rec lookup (sought_ident : identifier) (env : env) : term option =
   match env with
   | [] -> None
   | (ident, binding) :: _ when ident = sought_ident -> Some binding