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 (<vector2> get-x get-y zero?))
(define-class <vector2> ()
(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 <vector2>))
(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 <vector2>))
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 #<<generic> 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 (_ #<<vector2> 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" (#<<gen…> …) …)
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.
