Updated.

trees/main.rkt

@@ -1,33 +1,36 @@
+;; The first three lines of this file were inserted by DrRacket. They record metadata
+;; about the language level of this file in a form that our tools can easily process.
 #reader(lib "htdp-intermediate-reader.ss" "lang")((modname main) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #f #t none #f () #f)))
-
+#|; A MaybeTree is one of
-; A MaybeTree is one of
 ; - (make-tree [Number MaybeTree MaybeTree])
 (define-struct tree [n left right])
 ; - 'end
 
 (define sprout (make-tree 0 'end 'end))
 (define seedling (make-tree 5 sprout (make-tree 6 'end 'end)))
-(define sapling (make-tree 10 (make-tree 6 sprout 'end) (make-tree 12 'end 'end)))
+(define sapling (make-tree 10
+                           (make-tree 6 sprout 'end)
+                           (make-tree 12 'end 'end)))
 (define good-tree (make-tree 50 sapling (make-tree 100 'end 'end)))
 (define broke-tree (make-tree 5 good-tree good-tree))
 
-; Tree -> Bool
+; Tree t -> Bool
 ; Determines whether a Tree is a binary search tree.
 (define (bst? t)
-  (local [; Tree Number -> Bool
+  (local [; Tree t -> Bool
           ; Recursively checks left and right.
           (define (recurse t)
             (or (and (symbol? t) (symbol=? t 'end))
                 (and (acc-right (tree-right t) (tree-n t))
                      (acc-left (tree-left t) (tree-n t)))))
 
-          ; Tree Number -> Bool
+          ; Tree t, Number n -> Bool
           ; Accumulates the current number to check left.
           (define (acc-left t n)
             (or (and (symbol? t) (symbol=? t 'end))
                 (and (< (tree-n t) n) (recurse t))))
 
-          ; Tree Number -> Bool
+          ; Tree t, Number n -> Bool
           ; Accumulates the current number to check right.
           (define (acc-right t n)
             (or (and (symbol? t) (symbol=? t 'end))
@@ -38,4 +41,55 @@
 (check-expect (bst? sapling) #t)
 (check-expect (bst? good-tree) #t)
 (check-expect (bst? broke-tree) #f)
+|#
 
+; A Trie is a [Node]
+
+; A Node is a
+; (make-node [String c Boolean e [Node] l])
+; and represents a prefix tree. 'c' represents the node character, 'e' is a
+; flag for if the node marks the end of a word in the tree, and 'l' is the list
+; of child nodes.
+(define-struct node [c e l])
+
+(define example-trie
+  (list (make-node "a" #t
+               (list (make-node "n"  #t (list (make-node "d" #t '()) (make-node "t" #t '())))))
+    (make-node "b" #f
+               (list (make-node "e" #t (list (make-node "e" #t '()) (make-node "t" #t (list (make-node "t" #f (list (make-node "e" #f (list (make-node "r" #t '())))))))))))
+    (make-node "c" #f (list (make-node "a" #f (list (make-node "t" #t '())))))))
+
+; String w, Trie t -> Boolean
+; Determines whether the given word is in the given Trie.
+(define (in-trie? w t)
+  (local [; [Node] l, String wsf -> Boolean
+          ; Basically ormap of in?h on list of nodes but no lambda so this exists.
+          (define (childs? l wsf)
+            (and (not (empty? l))
+            (or (in?h (first l) wsf) (childs? (rest l) wsf))))
+
+          ; Node n, String wsf -> Boolean
+          ; Helper for in?. Accumulates word so far.
+          (define (in?h n wsf)
+            (or (and (string=? (string-append wsf (node-c n)) w) (node-e n)) (childs? (node-l n) (string-append wsf (node-c n)))))
+
+          ; Node n -> Boolean
+          ; Determines whether word is in the node or child nodes.
+          (define (in? n) (in?h n ""))] (ormap in? t)))
+
+(check-expect (in-trie? "cat" example-trie) #t)
+(check-expect (in-trie? "ca" example-trie) #f)
+(check-expect (in-trie? "catch" example-trie) #f)
+(check-expect (in-trie? "better" example-trie) #t)
+(check-expect (in-trie? "bee" example-trie) #t)
+(check-expect (in-trie? "beee" example-trie) #f)
+
+; [String] l -> Trie
+; Generates the trie for a list of strings.
+(define (strie l)
+  (local [; String w, Trie t -> Trie
+          ; Adds word w to a Trie.
+          (define (triadd w t)
+            (if (
+
+(check-exepct (strie '("and" "bee" "cat" "an" "a" "ant" "better" "bet" "be")) example-trie)