tweak calc improvements

Signed-off-by: Jim Pryor <profjim@jimpryor.net>

diff --git a/advanced_topics/calculator_improvements.mdwn b/advanced_topics/calculator_improvements.mdwn
index f6f179f..68bd39d 100644 (file)
--- a/advanced_topics/calculator_improvements.mdwn
+++ b/advanced_topics/calculator_improvements.mdwn
@@ -197,7 +197,7 @@ but instead to:
 
 Except, this isn't quite right. It's almost what we want, but not exactly. Can you see the flaw?
 
-The flaw is this: inside `new_closure`, what is `'f;` bound to? It's bound by `savedg'` to `orig_closure`, which in turn leaves `'f'` free (or bound to whatever existing value it had according to `savedg`). This isn't what we want. It'll break if we need to make applications of `Variable 'f'` which recurse more than once.
+The flaw is this: inside `new_closure`, what is `'f'` bound to? It's bound by `savedg'` to `orig_closure`, which in turn leaves `'f'` free (or bound to whatever existing value it had according to `savedg`). This isn't what we want. It'll break if we need to make applications of `Variable 'f'` which recurse more than once.
 
 What we really want is for `'f'` to be bound to `new_closure`, something like this:
 
@@ -222,12 +222,12 @@ If we implemented assignments as functions rather than as lists of pairs, the co
 
        | Let (var_to_bind, t1, t2) ->
                let value1 = eval t1 g
-               in let g' = fun var -> if var = var_to_bind value1 else g var
+               in let g' = fun var -> if var = var_to_bind then value1 else g var
                in eval t2 g'
        ...
        | Letrec (var_to_bind, t1, t2) ->
                let Closure (arg_var, body, savedg) = eval t1 g
-               in let rec savedg' = fun var -> if var = var_to_bind Closure (arg_var, body, savedg') else savedg var
+               in let rec savedg' = fun var -> if var = var_to_bind then Closure (arg_var, body, savedg') else savedg var
                in let g' = fun var -> if var = var_to_bind then Closure (arg_var, body, savedg') else g var
                in eval t2 g';;