From: Ramakrishnan Muthukrishnan Date: Mon, 21 Feb 2011 03:11:32 +0000 (+0530) Subject: solution to 3.26 X-Git-Url: https://git.rkrishnan.org/(%5B%5E?a=commitdiff_plain;h=f4c74f2f1152778229ed2940ea021538504135e8;p=sicp.git solution to 3.26 --- diff --git a/src/sicp/ex3_26.rkt b/src/sicp/ex3_26.rkt new file mode 100644 index 0000000..4feb501 --- /dev/null +++ b/src/sicp/ex3_26.rkt @@ -0,0 +1,69 @@ +#lang r5rs + +(define (make-entry k v) (cons k v)) +(define (key entry) (car entry)) +(define (value entry) (cdr entry)) +(define (set-key! entry k) (set-car! entry k)) +(define (set-value! entry v) (set-cdr! entry v)) +(define (null-entry? e) + (if (null? e) + #t + (or (null? (key e)) + (null? (value e))))) + +;(define (set-entry! k v e) +; (set-key! k e) +; (set-value! v e)) + +(define (make-node entry left right) + (cons entry (cons left (cons right '())))) + +(define (entry-node node) (car node)) +(define (left-node node) (car (cdr node))) +(define (right-node node) (car (cdr (cdr node)))) + +(define (make-tree) + (make-node (make-entry '() '()) '() '())) + +(define (entry-tree tree) + (entry-node tree)) + +(define (left-branch tree) + (left-node tree)) + +(define (right-branch tree) + (right-node tree)) + +(define (set-left-branch! tree val) + (set-car! (cdr tree) val)) + +(define (set-right-branch! tree val) + (set-car! (cdr (cdr tree)) val)) + +(define (set-entry! tree entry) + (set-car! tree entry)) + +(define (make-tree-node k v) + (make-node (make-entry k v) '() '())) + +(define (lookup k table) + (let ((e (entry-tree table))) + (cond + ((null-entry? e) #f) + ((= k (key e)) (value e)) + ((< k (key e)) (lookup k (left-branch table))) + ((> k (key e)) (lookup k (right-branch table)))))) + +(define (insert! k v table) + (cond + ((null-entry? (entry-tree table)) (set-entry! table (make-entry k v))) + ((= k (key (entry-tree table))) (set-value! (entry-tree table) v)) + ((< k (key (entry-tree table))) + (if (null? (left-branch table)) + (set-left-branch! table (make-tree-node k v)) + (insert! k v (left-branch table)))) + ((> k (key (entry-tree table))) + (if (null? (right-branch table)) + (set-right-branch! table (make-tree-node k v)) + (insert! k v (right-branch table))))) +'ok) \ No newline at end of file