Questions on a very simple class

[Alain De Vos]

Following code makes an "integerclass" with an "add" method :

#lang racket

(define (integerclass x)

  (define (getx)  x)
  (define (setx! x_new) (set! x x_new))
  (define (add y)(integerclass (+ x (y 'getx))))
  (lambda (message . args)
    (case message
        ((getx)      (apply getx    args))
        ((setx!)     (apply setx!   args))
        ((add)       (apply add     args))
      (else (error "POINT: Unknown message ->" message)))))

(define (myprint x) (print x)(newline))
(define p1 (integerclass 1))
(myprint (p1 'getx))
(define p2 (integerclass 2))
(myprint (p2 'getx))
(define p3 (p1 'add p2))
(myprint (p3 'getx))

Question 1 : can this code be inproved, are there "better patterns" one can you.
Question 2 : can i modify this code to use typed/racket. I tried but failed on the "apply" method in the code.

[Sage Gerard]

1. If the intention is to create a class, then I'd use the class form.

https://docs.racket-lang.org/reference/createclass.html#%28form._%28%28lib._racket%2Fprivate%2Fclass-internal..rkt%29._class%2A%29%29

Not that there's anything overtly wrong with using a closure, but common validation tasks re: inheritance, overriding, etc. all have to be done by hand here.

2. What specific error message did you get?

~slg

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[Alain De Vos]

When i try typed/racket :
#lang typed/racket

(define (integerclass x)
  (define (getx) x)

  (define (setx! [x_new : Integer]) (set! x x_new))
  (define (add [y : integerclass]) : integerclass (integerclass (+ 1 (y 'getx))))

  (lambda (message . args)
    (case message
        ((getx)      (apply getx    args))
        ((setx!)     (apply setx!   args))
        ((add)       (apply add     args))
      (else (error "POINT: Unknown message ->" message)))))

(define (myprint x) (print x)(newline))
(define p1 (integerclass 1))
(myprint (p1 'getx))
(define p2 (integerclass 2))
(myprint (p2 'getx))
(define p3 (p1 'add p2))
(myprint (p3 'getx))

I receive the errors,
On the line:
(define (add [y : integerclass]) : integerclass (integerclass (+ x (y 'getx))))
4 errors :
Type Checker: parse error in type; type name `integerclass' is unbound in: integerclass

Type Checker: parse error in type; type name `integerclass' is unbound in: integerclass

Type Checker: missing type for identifier;consider adding a type annotation with `:' identifier: integerclass in: integerclass
Type Checker: type mismatch expected: Number given: Any in: x

On the line :
((getx)      (apply getx    args))
Error :Type Checker: Bad arguments to function in `apply': Domain:  Arguments:  (Listof Any)
Other apply lines produce same errors.

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[Alain De Vos]

For the record, this worked:
#lang typed/racket
(require typed/racket/class)
(define aninteger%
  (class object%
    (super-new)
    (init-field [x : Integer 0])
    (: getxinternal Integer)
       (define getxinternal x)
    (: getx (-> Integer))
       (define/public (getx) getxinternal)))
(print (send (new aninteger% [x 2]) getx))