Question

LISP

1. [3 marks] Write a procedure called triangle that takes three numbers as arguments representing the three side-lengths of a triangle. The procedure should classify the triangle and return one of the following strings: "Equilateral" "Isoceles" "Scalene".
   E.g. (triangle 2 3 4) → "Scalene"
   E.g. (triangle 2 3 2) → "Isoceles"

Answer 1

LISP code for the above problem-

(defun read-side (side) (format t "Enter a value for side ~d: ~%" side) (read))

(defun triangle-p (a b c) (and (< a (+ b c)) (< b (+ a c)) (< c (+ a b))))

(defun equilateral-p (a b c) (= a b c))

(defun isoceles-p (a b c) (or (= a b) (= b c)))

(defun status-message (message a b c) (format t "The shape ~d,~d,~d ~a ~%" a b c message))

(defun classify-triangle (a b c)
    (cond ((not (triangle-p a b c)) nil)
              ((equilateral-p a b c) 'equilateral)
              ((isoceles-p a b c) 'isoceles)
                  (t 'triangle)))

(let* ((a (read-side 1)) (b (read-side 2)) (c (read-side 3)) (triangle-type (classify-triangle a b c)))
  (format t "classify triangle says ~a ~%" triangle-type)
  (cond ((eq 'equilateral triangle-type) (status-message "is an equilateral triangle." a b c))
        ((eq 'isoceles triangle-type) (status-message "is an isoceles triangle." a b c))
        ((eq 'triangle triangle-type) (status-message "is a "Scalene triangle." a b c))
        (t (status-message "is not a triangle." a b c))))

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