GNU bug report logs - #37461
Methods added to primitive generics don't always work

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From: Rob Browning <rlb <at> defaultvalue.org>
To: 37461 <at> debbugs.gnu.org
Cc: control <at> debbugs.gnu.org
Subject: bug#37461: define-generic doesn't promote equal? to generic
Date: Sat, 21 Sep 2019 10:15:41 -0500

retitle 37461 Methods added to primitive generics don't always work
thanks

Rob Browning <rlb <at> defaultvalue.org> writes:

> A re-export doesn't affect the module using the re-exporter, and export
> and replace both fail with "Unbound variable: equal?", even though
> there's a (define equal?  ...)  in the module.

It looks like equal? isn't changed by define-generic, etc. because it
already has "generic-capability?".  And in fact, I can see that defining
a method on it does alter its primitive-generic-generic, but then
dispatch to the new method doesn't always seem to work (or perhaps I
just misunderstand the dispatch rules).

Here a one argument specialization doesn't work, but a two argument
specialization does -- for new classes, but not for a "standard" class
like <string>:

  scheme@(guile-user)> (use-modules (oop goops))
  scheme@(guile-user)> (primitive-generic-generic equal?)
  $1 = #<<generic> equal? (1)>

  scheme@(guile-user)> (define-class <foo> () (data))
  scheme@(guile-user)> (define-method (equal? (x <foo>)) 'x)
  scheme@(guile-user)> (primitive-generic-generic equal?)
  $2 = #<<generic> equal? (2)>
  scheme@(guile-user)> (equal? (make <foo>))
  $3 = #t

  scheme@(guile-user)> (define-method (equal? (x <foo>) (y <foo>)) 'x)
  $4 = #<<generic> equal? (3)>
  scheme@(guile-user)> (equal? (make <foo>) (make <foo>))
  $5 = x

  scheme@(guile-user)> (define-method (equal? (x <string>) (y <string>)) 'x)
  $6 = #<<generic> equal? (4)>
  scheme@(guile-user)> (equal? "x" "y")
  $7 = #f

Thanks
-- 
Rob Browning
rlb @defaultvalue.org and @debian.org
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