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fmi-fp-exercises/scheme-homework/01-fun-with-digits.rkt
@startrunner startrunner Scheme Homework 781ce76 11 days ago
51 lines (42 sloc) 1.79 KB
; Искаме да дефинираме следните имена: one, two, three, ..., nine, plus, minus, times, div,
; така че извиквания от типа на (one (plus (three))) (операция с точно две операнди) да връщат легитимни числови стойности (в този случай - 4)
; Още малко примери:
; (three (times (five))) -> 15
; (nine (div (three))) -> 3
; (eight (minus (four))) -> 4
;


#lang racket
(require rackunit rackunit/text-ui)

(define (digit-function digit)
  {lambda args
    {cond
      [(empty? args)           digit]
      [(empty? (cdr args))     ((car args) digit)]
      [else                    null]}})

(define (operation-function operation)
  {lambda (rightArg) {lambda (leftArg) {operation leftArg rightArg}}})

(define zero    (digit-function 0))
(define one     (digit-function 1))
(define two     (digit-function 2))
(define three   (digit-function 3))
(define four    (digit-function 4))
(define five    (digit-function 5))
(define six     (digit-function 6))
(define seven   (digit-function 7))
(define eight   (digit-function 8))
(define nine    (digit-function 9))

(define plus    (operation-function +))
(define minus   (operation-function -))
(define times   (operation-function *))
(define div     (operation-function /))

;Test code

(define fun-with-digits-tests
  (test-suite "Fun with digits tests"
    (test-case "Digits work as singleton expressions"
               (check-eq? (five) 5))
    ;Division of coprimes is best for testing since we are unlikely to get the right answer with wrong code
    (test-case "Division is chained properly"
               {check-true (=(five (div (six (div (eight (div (three))))))) (/ 5  (/ 6 (/ 8 3))))})
  )
)

(run-tests fun-with-digits-tests 'verbose)

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