I was playing with GOOPS and noticed this bug:

> scheme@(guile-user)> (use-modules (oop goops))
> scheme@(guile-user)> (define-method (+ (x <list>) (y <list>)) (next-method))
> scheme@(guile-user)> (+ '() '())
> oop/goops/compile.scm:48:35: In procedure car:
> oop/goops/compile.scm:48:35: Wrong type argument in position 1 (expecting pair): ()
> 
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,bt
> 
> In standard input:
>       8:0  4 (#<procedure a879a0 at standard input:8:0 ()>)
> In oop/goops/dispatch.scm:
>     231:9  3 (cache-miss #<<generic> + (1)> (() ()))
>     246:4  2 (memoize-effective-method! #<<generic> + (1)> (() ()) (#))
> In oop/goops/compile.scm:
>     54:13  1 (compute-cmethod (#<<method> (<list> <list>) afc640>) (…))
>     48:34  0 (compute-cmethod () (#<<class> <null> befd20> #<<clas…>))

With the attached patch applied, here's what happens instead:

> scheme@(guile-user)> (define-method (+ (x <list>) (y <list>)) (next-method))
> scheme@(guile-user)> (+ '() '())
> ERROR: In procedure scm-error:
> ERROR: No next method when calling #<<generic> + (1)>
> with arguments (() ())
> 
> Entering a new prompt.  Type `,bt' for a backtrace or `,q' to continue.
> scheme@(guile-user) [1]> ,q

I confess I don't know much about GOOPS, but I think the fix is pretty
obvious.

    Best,
     Mark