20th December 2 hours exam needs dr.racket
Question Description
following is a sample
;; The first three lines of this file were inserted by DrRacket. They record metadata
;; about the language level of this file in a form that our tools can easily process.
#reader(lib "htdp-advanced-reader.ss" "lang")((modname 2016W1-F-solution) (read-case-sensitive #t) (teachpacks ()) (htdp-settings #(#t constructor repeating-decimal #t #t none #f () #f)))
(require 2htdp/image)
(require spd/tags)
(@problem 1)
;; The following signature purpose, stub, and check-expects for the function
;; count-trues are provided for you to use with Problems 1A, 1B, 1C and 1D.
;;
;; Read Problems 1A, 1B, 1C and 1D before you start.
(@htdf count-trues)
(@signature (listof Boolean) -> Natural)
;; produce the number of trues in the list
(check-expect (count-trues empty) 0)
(check-expect (count-trues (list false true true true false false))
3)
(check-expect (count-trues (list true true false true true true true))
6)
;(define (count-trues x) 0) ;stub
;; Problem 1A:
;;
;; Write a non-tail recursive function definition for count-trues using the
;; (listof X) template.
;;
;; Include a template tag.
;; 5, 1 each for
;;
;; - template tag
;; - template is apparent
;; - base case result is correct (0)
;; - combination is correct (+)
;; - selection behaviour is correct (true and false cases)
(@template (listof Boolean))
#;
(define (count-trues lob)
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