Re: Modules and GOOPS

[Jan Wedekind]

On Wed, 27 Jul 2016, Kovacsics Róbert wrote:

> Hello!
>
> I have trouble with getting GOOPS and modules to co-operate. What I am
> trying to do is to have 'A subclass B' where A is something akin to an
> abstract class, that is it has generic "x" for which it provides no
> implementation. This is my minimum broken example:
>
>
> ; <mbe/a.scm>=
> (define-module (mbe a)
>  #:use-module (oop goops)
>  #:export (<a> x y))
>
> (define-class <a> ())
>
> (define-generic x)
> (define-generic y)
>
> (define-method (y (a <a>))
>  (display (x a)))
>
> ; <mbe/b.scm>=
> (define-module (mbe b)
>  #:use-module (oop goops)
>  #:use-module (mbe a)
>  #:export (<b> x))
>
> (define-class <b> (<a>))
>
> (define-method (x (b <b>))
>  'b)
>
> ; <mbe/test.scm>=
> (define-module (mbe test)
>  #:use-module (oop goops)
>  #:use-module (mbe a)
>  #:use-module (mbe b)
>  #:duplicates (merge-generics))
>
> (y (make <b>))
>
>
> and when I type "(use-modules (mbe test))" in guile, I get
>
>
> While compiling expression:
> ERROR: No applicable method for #<<generic> x (0)> in call (x #<<b> 23ccdd0>)
>
> (which shows that the generic function "x" has no implementation as
> far as I can work it out, due to accessibility. When I don't use
> separate modules, it works.)
>
> Am I using the right sort of approach? I was thinking modules, for
> extensibility.

Having mbe/b.scm *not* export "x" works but I am not sure whether that is 
the solution you are looking for:


; <mbe/a.scm>=
(define-module (mbe a)
  #:use-module (oop goops)
  #:export (<a> x y))

(define-class <a> ())

(define-generic x)
(define-generic y)

(define-method (y (a <a>))
  (display (x a)))

; <mbe/b.scm>=
(define-module (mbe b)
  #:use-module (oop goops)
  #:use-module (mbe a)
  #:export (<b>))

(define-class <b> (<a>))

(define-method (x (b <b>))
  'b)

; <mbe/test.scm>=
(define-module (mbe test)
  #:use-module (oop goops)
  #:use-module (mbe a)
  #:use-module (mbe b)
  #:duplicates (merge-generics))

(y (make <b>))


Has anybody managed to get the "merge-generics" handler to work? I used to 
have this in my $HOME/.guile configuration but it didn't seem to have any 
effect:

(default-duplicate-binding-handler '(merge-generics replace warn-override-core 
warn last))