X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment4.mdwn;h=12c1ef2a213e195cd9f88066baf9e8e53e9d5c46;hp=cd927873638b3ffbd724d09b599e2e1f211d5c89;hb=3641a9827575d2eba30d316395eb3db7c45a1477;hpb=50a9ebe3ecc8c1b392c8118546ded369fe39d1d4
diff --git a/assignment4.mdwn b/assignment4.mdwn
index cd927873..12c1ef2a 100644
--- a/assignment4.mdwn
+++ b/assignment4.mdwn
@@ -38,7 +38,9 @@ You'll need an operation `make_leaf` that turns a label into a new leaf. You'll
need an operation `make_node` that takes two subtrees (perhaps leaves, perhaps
other nodes) and joins them into a new tree. You'll need an operation `isleaf`
that tells you whether a given tree is a leaf. And an operation `extract_label`
-that tells you what value is associated with a given leaf.
+that tells you what value is associated with a given leaf. And an operation
+`extract_left` that tells you what the left subtree is of a tree that isn't a
+leaf. (Presumably, `extract_right` will work similarly.)
The **fringe** of a leaf-labeled tree is the list of values at its leaves,
ordered from left to right. For example, the fringe of this tree:
@@ -49,7 +51,7 @@ ordered from left to right. For example, the fringe of this tree:
/ \
1 2
-is [1;2;3]. And that is also the fringe of this tree:
+is `[1;2;3]`. And that is also the fringe of this tree:
.
/ \
@@ -66,15 +68,13 @@ lists to see if they're equal. (You just programmed this above.)
Write the fringe-enumeration function. It should work on the implementation of
trees you designed in the previous step.
-
-(See [[hints/Assignment 4 hint 3]] if you need some hints.)
#Mutually-recursive functions#
-
+
- (Challenging.) One way to define the function `even` is to have it hand off
part of the work to another function `odd`:
@@ -132,7 +132,7 @@ definitions of `even` and `odd`?
notes](/week3/#index4h2) as a model, construct a pair `Y1` and `Y2` that behave
in the way described.
-(See [[hints/Assignment 4 hint 4]] if you need some hints.)
+(See [[hints/Assignment 4 hint 3]] if you need some hints.)