From: Jim Pryor <profjim@jimpryor.net>
Date: Thu, 25 Nov 2010 16:57:16 +0000 (-0500)
Subject: tweak calc improvements
X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=commitdiff_plain;h=2cef07bcbf221a75e0cf0da553be6566a206d68f

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 f6f179fb..68bd39d8 100644
--- 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';;