X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?a=blobdiff_plain;f=assignment4.mdwn;h=7073dc6b188c3c022289937e451e00840ddf0f30;hb=950285ea353793fdd9ddcfa7e6e54b4c1f73601c;hp=cd927873638b3ffbd724d09b599e2e1f211d5c89;hpb=f3e44d1a6911bf2bf8376bd3b711adf63cdeee13;p=lambda.git diff --git a/assignment4.mdwn b/assignment4.mdwn index cd927873..7073dc6b 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: . / \ @@ -74,7 +76,7 @@ trees you designed in the previous step. #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`: