;; Author: Isaac H. Lopez Diaz <[email protected]>

;; Description: Functions from The Little Schemer

;; Test to see if value is an atom

(define atom?

(lambda (x)

(and (not (pair? x))

(not (null? x)))))

;; Increase by 1 the current number

(define add1

(lambda (x)

(+ x 1)))

;; Decrease by 1 the current number

(define sub1

(lambda (x)

(- x 1)))

;; Test whether an atom is on a list

(define member?

(lambda (a lat)

(cond

((null? lat) #f)

(else (or (eq? a (car lat))

(member? a (cdr lat)))))))

;; Test whether a number is equal to one

(define one?

(lambda (x)

(= x 1)))

;; Function that extracts the leftmost atom

(define leftmost

(lambda (l)

(cond

((atom? (car l))

(car l))

(else (leftmost (car l))))))