[m-users.] IO argument clobbering

[Volker Wysk]

Am Dienstag, dem 18.07.2023 um 19:55 +1000 schrieb Zoltan Somogyi:
> On 2023-07-18 11:44 +02:00 CEST, "Volker Wysk" <post at volker-wysk.de> wrote:
> > Am Dienstag, dem 18.07.2023 um 18:32 +1000 schrieb Peter Wang:
> > > To clarify, you CAN approximate a higher-order term with the inst `ground',
> > > because the term has no variables (variables essentially meaning "holes"
> > > in the term that are not yet filled in).
> > > 
> > > What you can't do is CALL a higher-order term approximated by `ground'
> > > because `ground' does not include any higher-order inst information.
> > 
> > Hmmm... Why would you want to approximate a higher order inst with a ground
> > inst? Isn't calling the term as a function or predicate the only thing you
> > can do with it?
> 
> You wouldn't WANT to, but sometimes, as with the code that started off
> this email thread, you DO, because you either don't KNOW that you have to
> specify the higher order inst for the higher order value, or because you
> simplify forget.

Yes, that's Sean's case.

> When you write "callback::in" as the type and mode of an argument,
> the type says that the only thing you can do with the argument is call it,
> but the inst says you can't call it, because the compiler does not know
> the modes of the predicate's arguments. 

Yes, I've understood with your explanation (previous mail).

> (In the original example, callback
> is a predicate type, but the same would be true for any function whose mode
> was not the standard function mode.) This is obviously :-) a problem.
> 
> Peter is right; this issue needs better explanation in the error messages
> that it gives rise to. I will look into it.

Agreed. I find the error messages which occur in conjunction with insts hard
to follow.

Cheers,
Volker

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