X-Git-Url: http://lambda.jimpryor.net/git/gitweb.cgi?p=lambda.git;a=blobdiff_plain;f=assignment4.mdwn;h=3e3b71841c6fa51e546c65c4c527cf798836de40;hp=cd927873638b3ffbd724d09b599e2e1f211d5c89;hb=95dad38cb4aa443a3dde5bad742d53f023b0ca33;hpb=50a9ebe3ecc8c1b392c8118546ded369fe39d1d4;ds=sidebyside diff --git a/assignment4.mdwn b/assignment4.mdwn index cd927873..3e3b7184 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: