Re: More static type fun.

From: Stephen J. Bevan (stephen_at_dino.dnsalias.com)
Date: 10/30/03 

Date: Thu, 30 Oct 2003 03:18:43 GMT

Joe Marshall <jrm@ccs.neu.edu> writes:
> The point of test2 was to demonstrate that F needed to be a polytype
> function. It was used with an int argument and with an int->int
> argument. In addition, when presented with a particular int->int
> argument it needed to return a *different* int->int argument (this was
> to throw a monkey wrench in for all those compilers that might
> have noticed that F(x) => x for all x).

I understood the point of the test, I just pointed out that since
equality isn't defined over functions in some languages then
*some* kind of change would have to be made to allow for that.
Since you didn't proffer any modified Common Lisp that used a wrapper
it wasn't clear what kind of wrapper would be acceptable.

> (It is a bit disturbing to see the words `some kind of datatype that
> identity can be defined over', however. I would assume that identity
> need not be defined *over* any datatype, it ought to work for any
> expressable value.)

Perhaps we have a terminology problem. If I define a structure (or
record, call it what you will) in a language that doesn't have any
kind of implicit "pointer/address equality" over values then equality
over that structure is either hard-wired in the language (say
recursive structural equivalence on each field) or the language allows
the user to define equality on a per structure basis (again in terms
of the fields).

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