Re: "Current" solution for generalized set!

[Mikael Djurfeldt <mdj@nada.kth.se>]

Ken Anderson <kanderso@bbn.com> writes:

> Your proposal reminds me of funcallable-instances, fin's, of PCL.  These
> were functions with slots.  Fin's were the building blocks that generic
> functions were built on top of.  

The exist in Goops, and are called "entities".

All instances of classes which have a subclass of <entity-class> as
metaclass behave as procedures.  You set the procedure with
`set-object-procedure!'.

I see two problems with using them as a representation of the
<getter-with-setter> (or <procedure-with-setter>):

1. Since Goops is not a part of guile-core but a separate package, and
   since set! is supposed to belong to guile-core, we can't rely too
   heavily on object system mechanisms in guile-core.  For this
   reason, although it would be nice, we can't let our getter/setter
   pair be a subclass of <generic>.

   However, there is support for basic entities in guile-core, but
   since there is probably no big advantage in using that
   representation instead of the currently suggested closures with
   setter slot.

2. It is essential that there doesn't exist a way to mutate the setter
   of a getter.  For this we have to include support for read-only
   slots.  This is perhaps possible to add to Goops, though.

So, yes, to use an entity as the representation for a
<procedure-with-setter> may be an alternative.

/mdj