From: Ramakrishnan Muthukrishnan Date: Sun, 19 Sep 2010 18:45:46 +0000 (+0530) Subject: some misc utilities X-Git-Url: https://git.rkrishnan.org/(%5B%5E?a=commitdiff_plain;h=6256e3d6aa85a9758382f8ee1d5dc7df83fa6c75;p=sicp.git some misc utilities --- diff --git a/src/sicp/goodies.rkt b/src/sicp/goodies.rkt new file mode 100644 index 0000000..49e8b25 --- /dev/null +++ b/src/sicp/goodies.rkt @@ -0,0 +1,17 @@ +#lang racket +(provide distinct) + +(define (member? x lst) + (cond + [(empty? lst) #f] + [(equal? (first lst) x) #t] + [else (member? x (rest lst))])) + +(define (distinct lst) + (cond + [(empty? lst) '()] + [(member? (first lst) (rest lst)) (distinct (rest lst))] + [else (cons (first lst) + (distinct (rest lst)))])) + + \ No newline at end of file diff --git a/src/sicp/misc.rkt b/src/sicp/misc.rkt new file mode 100644 index 0000000..8234215 --- /dev/null +++ b/src/sicp/misc.rkt @@ -0,0 +1,58 @@ +#lang racket + +(define (map1 f list) + (cond + [(empty? list) '()] + [else (cons (f (first list)) + (map1 f (rest list)))])) + +(define (mymap f lists) + (cond + [(empty? (first lists)) '()] + [else (cons (apply f (map1 first lists)) + (mymap f (map1 rest lists)))])) + +;; 2.28 +(define (fringe coll) + (cond + [(null? coll) '()] + [(not (pair? coll)) (list coll)] + [else (append (fringe (first coll)) + (fringe (rest coll)))])) + +(define (scale-tree tree factor) + (map (lambda (subtree) + (if (pair? subtree) + (scale-tree subtree factor) + (* subtree factor))) + tree)) + +;; 2.30 +(define (square-tree1 tree) + (map (lambda (subtree) + (if (pair? subtree) + (square-tree1 subtree) + (* subtree subtree))) + tree)) + +(define (square-tree2 tree) + (cond + [(null? tree) '()] + [(not (pair? tree)) (* tree tree)] + [else (cons (square-tree2 (car tree)) + (square-tree2 (cdr tree)))])) + +(define (fringe1 tree) + (map (lambda (subtree) + (if (not (pair? subtree)) + subtree + (fringe1 subtree))) + tree)) + + +(define (tree-map f tree) + (map (lambda (subtree) + (if (pair? subtree) + (tree-map f subtree) + (f subtree))) + tree)) diff --git a/src/sicp/utils.rkt b/src/sicp/utils.rkt new file mode 100644 index 0000000..b81f601 --- /dev/null +++ b/src/sicp/utils.rkt @@ -0,0 +1,16 @@ +#lang racket + +(define (square x) (* x x)) + +(define (abs x) + (if (< x 0) (- x) x)) + +(define (divides? a b) + (= (remainder b a) 0)) + +(define (gcd a b) + (if (= b 0) + a + (gcd b (remainder a b)))) + +(provide square) \ No newline at end of file