This does not work. If I remove the export of ‘zero?’ I get another error:
scheme@(guile-user)> (zero? (make ))
:3:1: :3:1: In procedure =: Wrong type:
#< 106606e20>
Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
scheme@(guile-user) [1]> ,bt
In current input:
3:1 0 (_)
scheme@(guile-user) [1]>
That is why I was exporting ‘zero?’ to begin with. I do not have to export ‘+’
or ‘-‘ for example.
> On 19 Apr 2017, at 17:13, GNU bug Tracking System
> wrote:
>
> Your bug report
>
> #26026: Defining a method named zero? breaks primitive zero?
>
> which was filed against the guile package, has been closed.
>
> The explanation is attached below, along with your original report.
> If you require more details, please reply to 26...@debbugs.gnu.org.
>
> --
> 26026: http://debbugs.gnu.org/cgi/bugreport.cgi?bug=26026
> GNU Bug Tracking System
> Contact help-debb...@gnu.org with problems
>
> From: Andy Wingo
> Subject: Re: bug#26026: Defining a method named zero? breaks primitive zero?
> Date: 19 April 2017 at 17:12:12 GMT+2
> To: Alejandro Sanchez
> Cc: 26026-d...@debbugs.gnu.org
>
>
> On Wed 08 Mar 2017 12:07, Alejandro Sanchez writes:
>
>> If I define a ‘zero?’ predicate method for a custom class the primitive
>> ‘zero?’ is lost. Here is a simple vector module:
>>
>> ;;; File vector2.scm
>> (define-module (vector2)
>>#:use-module (oop goops)
>>#:export ( get-x get-y zero?))
>>
>> (define-class ()
>>(x #:init-value 0 #:getter get-x #:init-keyword #:x)
>>(y #:init-value 0 #:getter get-y #:init-keyword #:y) )
>>
>> (define-generic zero?)
>> (define-method (zero? (v ))
>>(and (zero? (get-x v))
>> (zero? (get-y v
>>
>> In the Guile REPL try executing the following code:
>>
>> scheme@(guile-user)> (use-modules (oop goops) (vector2))
>> scheme@(guile-user)> (zero? (make ))
>>
>> This will display
>>
>> WARNING: (guile-user): `zero?' imported from both (ice-9 r5rs) and
>> (vector2)
>> ERROR: In procedure scm-error:
>> ERROR: No applicable method for #< zero? (1)> in call (zero? 0)
>>
>> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
>> scheme@(guile-user) [1]> ,bt
>> In vector2.scm:
>> 11:7 2 (_ #< 105e87e00>)
>> In oop/goops.scm:
>> 1438:4 1 (cache-miss 0)
>> In unknown file:
>> 0 (scm-error goops-error #f "No applicable method for ~S in
>> call ~S" (#< …) …)
>>
>> Apparently the problem is that ‘zero?’ is defined in two modules and
>> the vector2 definition overrides it. This isn’t the case with other
>> primitives like ‘+’ or ‘*’, so this seems like a bug? I had built
>> Guile from HEAD a few days ago, my package manager shows 6fff84d as
>> the version number, so I guess that must be the hash of the commit
>> HEAD was pointing to at that time.
>
> Actually the (vector2) module makes a fresh definition for zero?. You
> can tell because zero? is in its export list. So instead of extending
> the primitive-generic that is zero?, you are making a new definition.
> See:
>
> scheme@(guile-user)> (define-module (foo) #:export (zero?))
> $1 = #
> scheme@(foo)> (zero? 0)
> :4:0: :4:0: Unbound variable: zero?
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
>
> If you want to extend a primitive-generic, then do that by not exporting
> zero?. In a way it's like mutating the primitive in place, giving it
> additional powers.
>
> Andy
>
>
>
>
> From: Alejandro Sanchez
> Subject: Defining a method named zero? breaks primitive zero?
> Date: 8 March 2017 at 12:07:56 GMT+1
> To: bug-guile@gnu.org
>
>
> If I define a ‘zero?’ predicate method for a custom class the primitive
> ‘zero?’ is lost. Here is a simple vector module:
>
> ;;; File vector2.scm
> (define-module (vector2)
> #:use-module (oop goops)
> #:export ( get-x get-y zero?))
>
> (define-class ()
> (x #:init-value 0 #:getter get-x #:init-keyword #:x)
> (y #:init-value 0 #:getter get-y #:init-keyword #:y) )
>
> (define-generic zero?)
> (define-method (zero? (v ))
> (and (zero? (get-x v))
> (zero? (get-y v
>
> In the Guile REPL try executing the following code:
>
> scheme@(guile-user)> (use-modules (oop goops) (vector2))
> scheme@(guile-user)> (zero? (make ))
>
> This will display
>
> WARNING: (guile-user): `zero?' imported from both (ice-9 r5rs) and
> (vector2)
> ERROR: In procedure scm-error:
> ERROR: No applicable method for #< zero? (1)> in call (zero? 0)
>
> Entering a new prompt. Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> In vector2.scm:
>11:7 2 (_ #< 105e87e00>)
> In oop/goops.scm:
> 1
