RE: define-typed: checking values on proc entry and exit

[Maxime Devos via General Guile related discussions <guile-user@gnu.org>]

>Hello,
>
>not sure to understand but does GOOPS (Guile object model) allow some sort
of check to the argument but perhaps it is only inherent to the procedures
of a 'class' in the object model?

I don’t know what ‘procedures of a class’ means, but otherwise yes, with the caveat that the check must be a type-check, in the sense that it checks whether the argument is of a certain class. 

The documentation https://www.gnu.org/software/guile/manual/html_node/Methods-and-Generic-Functions.html has a bunch of examples. I recommend reading it. (Also note that <number> is a class.)

Now, that the check must be a type-check isn’t actually much of a limitation, since you can just check other conditions in the body and call next-method when it doesn’t match.  (I’m not entirely sure though, I wonder what happens if you define a method of a generic with the same type signature as an another method of the generic).

Best regards,
Maxime Devos.