Re: difficulty of writing translators

[Marius Vollmer <mvo@zagadka.ping.de>]

Per Bothner <bothner@cygnus.com> writes:

> > I think Common Lisp defines it as something like
> >
> >    `((setter f) ,@args value)
> > that is, the value is the last argument to the setter function.
> 
> Nope.  The new value is the first argument to the stter function
> in Common Lisp, as in Kawa, and for the same reason:  The need
> to handle functions that take optional, keyword, or rest parameters.

I agree that using the value as the first parameter is easier.  But
CLtL2 says on pages 146:

    (defsetf access-fn update-fn [docstring])

    The UPDATE-FN must name a function (or macro) that takes one more
    argument than ACCESS-FN takes.  When `setf' is given a place that
    is a call on ACCESS-FN, it expands into a call to UPDATE-FN that
    is given all the arguments to ACCESS-FN and also, as its last
    argument, the new value (which must be returned by UPDATE-FN as
    its value).

This (and the following example) is where I got the idea that the
value comes last.

> It is easy to prepend an extra required parameter as the new
> first parameter to an existing parameter list;  appending a new
> argment at the end of a parameter list is much messier, in both
> Lisp and Scheme.

Yes, but this re-shuffling of arguments happens at macro-expansion
time, no?