Re: [racket-users] Questions on a very simple class

[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 getxargs))
((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 getxargs))
Error :Type Checker: Bad arguments to function in `apply': Domain:  
Arguments:  (Listof Any)
Other apply lines produce same errors.

On Sunday, February 16, 2020 at 12:25:41 AM UTC+1, Sage Gerard wrote:
>
> 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*
>
>
> ‐‐‐ Original Message ‐‐‐
> On Saturday, February 15, 2020 6:18 PM, Alain De Vos  > wrote:
>
>
> 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 getxargs))
> ((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.
>
>
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>  
> 
> .
>
>
>

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Re: [racket-users] Questions on a very simple class

[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

‐‐‐ Original Message ‐‐‐
On Saturday, February 15, 2020 6:18 PM, Alain De Vos  
wrote:

> 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 getxargs))
> ((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.
>
> --
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> "Racket Users" group.
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