X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment4.mdwn;h=9b7ec2c028622dc92e17dced54403aa6043b8896;hp=3e3b71841c6fa51e546c65c4c527cf798836de40;hb=4d3716c93c54b77c70549da836c90d9683fadb41;hpb=befb1d4a74380348118ed36c090f9eb1bbac1996 diff --git a/assignment4.mdwn b/assignment4.mdwn index 3e3b7184..9b7ec2c0 100644 --- a/assignment4.mdwn +++ b/assignment4.mdwn @@ -51,7 +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: . / \ @@ -64,19 +64,22 @@ return later in the term to the problem of determining when two trees have the same fringe. For now, one straightforward way to determine this would be: enumerate the fringe of the first tree. That gives you a list. Enumerate the fringe of the second tree. That also gives you a list. Then compare the two -lists to see if they're equal. (You just programmed this above.) +lists to see if they're equal. -Write the fringe-enumeration function. It should work on the implementation of -trees you designed in the previous step. +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.) +Then combine this with the list comparison function you wrote for question 2, +to yield a same-fringe detector. (To use your list comparison function, you'll +have to make sure you only use Church numerals as the labels of your leaves, +though nothing enforces this self-discipline.) #Mutually-recursive functions# -
+
1. (Challenging.) One way to define the function `even` is to have it hand off part of the work to another function `odd`: @@ -134,7 +137,7 @@ 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.)