Question

Write a Scheme predicate function that tests for the structural equality of two given lists. Two lists are structurally equal if they have the same list structure, although their atoms may be different.

Answer 1

Program plan:

• Two lists are structurally equal if they have the same list structure, although their atoms may be different.

• So we are going to write a function which checks if elements in both the list at same position are atoms or not.

• If yes then it should return true else false.

Program:

#lang scheme

( define (structurally-equal list1 list2)

(cond ((and (null? list1) (null? list2)) #t)

((or (null? list1) (null? list2)) #f)

((and (atom? (car list1)) (atom? (car list2)))

(structurally-equal (cdr list1) (cdr list2)))

((or (atom? (car list1)) (atom? (car list2))) #f)

(else (and (structurally-equal (car list1) (car list2))

(structurally-equal (cdr list1) (cdr list2) )))))

( define (atom? x) (not (or (pair? x) (null? x))))