CODEWITHSUNDEEP
schemeracket
San Gyeol Kang
San Gyeol Kang

Reputation: 110

how to make predicates function? in scheme

i'm trying to make predicates functions

datatype definition

(define-datatype expression expression?
  (const-exp (num number?))
  (var-exp (var symbol?))
  (zero?-exp (exp1 expression?))
  (diff-exp (exp1 expression?)
            (exp2 expression?)))

if argument is #2(struct:const-exp 7) then print #t

if argument is #2(struct:var-exp x) then print #f

(define const-exp? ... )

it would be honor if you help me

Upvotes: 0

Views: 1084

Answers (1)

uselpa
uselpa

Reputation: 18917

So my guess is that you are studying Essentials of Programming Languages and probably use Racket as your environment.

If that is true, you should probably use cases here:

(define (const-exp? e)
  (cases expression e
    (const-exp (num) #t)
    (else #f)))

then

> (const-exp? (const-exp 7))
#t
> (const-exp? (var-exp 'x))
#f

Upvotes: 2

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