X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment2.mdwn;h=85f63f3678a315f45e11dbd904c3c2f3ed98b3d2;hp=4f80620631159be4834260dabe32e119cb6cef1a;hb=701e1a701a0275a6a0294cba81df0e1984fa2768;hpb=7bb54cf783a20dd6f8ff464f5be97e72b87f4045;ds=sidebyside

diff --git a/assignment2.mdwn b/assignment2.mdwn
index 4f806206..85f63f36 100644
--- a/assignment2.mdwn
+++ b/assignment2.mdwn
@@ -1,3 +1,6 @@
+For these assignments, you'll probably want to use a "lambda calculator" to check your work. This accepts any grammatical lambda expression and reduces it to normal form, when possible. See the page on [[using the programming languages]] for instructions and links about setting this up.
+
+
 More Lambda Practice
 --------------------
 
@@ -56,6 +59,7 @@ The `junk` in `extract-head` is what you get back if you evaluate:
 As we said, the predecessor and the extract-tail functions are harder to define. We'll just give you one implementation of these, so that you'll be able to test and evaluate lambda-expressions using them in Scheme or OCaml.
 
 <pre><code>predecesor &equiv; (\shift n. n shift (make-pair zero junk) get-second) (\pair. pair (\fst snd. make-pair (successor fst) fst))
+
 extract-tail &equiv; (\shift lst. lst shift (make-pair empty junk) get-second) (\hd pair. pair (\fst snd. make-pair (make-list hd fst) fst))</code></pre>
 
 The `junk` is what you get back if you evaluate:
@@ -87,7 +91,7 @@ For these exercises, assume that `LIST` is the result of evaluating:
 
 should evaluate to a list containing just those of `a`, `b`, `c`, `d`, and `e` such that `f` applied to them evaluates to `true`.
 
-<LI>How would you implement map using the either the version 1 or the version 2 implementation of lists?
+<LI>What goes wrong when we try to apply these techniques using the version 1 or version 2 implementation of lists?
 
 <LI>Our version 3 implementation of the numbers are usually called "Church numerals". If `m` is a Church numeral, then `m s z` applies the function `s` to the result of applying `s` to ... to `z`, for a total of *m* applications of `s`, where *m* is the number that `m` represents or encodes.
 
@@ -103,6 +107,6 @@ Given the primitive arithmetic functions above, how would you implement the less
 	less-than-or-equal two one ~~> false
 	less-than-or-equal two two ~~> true
 
-You'll need to make use of the predecessor function, but it's not important to understand how the implementation we gave above works. You can treat it as a black box.
+You'll need to make use of the predecessor function, but it's not essential to understand how the implementation we gave above works. You can treat it as a black box.
 </OL>