Re: Issue: FUNCTION-DECLARATION (version 1)

[David N Gray <Gray@DSG.csc.ti.com>]

> CLtL permits ambiguous FUNCTION declarations.  One can say
>   (DECLARE (FUNCTION F (VECTOR INTEGER) T))
> to indicate that the function binding for F is of a certain type.  Yet
> one can also say
>   (DECLARE (FUNCTION X Y Z))
> to indicate that the variables X, Y, and Z have values which are functions.

Well, that depends on how you read it.  I always assumed that it was just
an oversight that page 158 doesn't mention that FUNCTION is an exception
to the list in table 4-1 since the next page gives it a different meaning.
Are there any implementations that actually try to support it both ways?
Actually, now that I think about it, both forms could be supported since
there isn't really any ambiguity -- in one case the third element of the
declaration specifier must be a list and in the other it must be a non-nil
symbol if present.

> Proposal (FUNCTION-DECLARATION:DELETE)
> 
> The declaration (FUNCTION name argtypes valtypes) is no longer permitted
> to be an abbreviation for (FTYPE (FUNCTION argtypes valtypes) name).
> 
> The declaration (FUNCTION var1 var2) would just be an abbreviation for
> (TYPE FUNCTION var1 var2).

Maybe this would have been cleaner, but I don't see sufficient
justification for making an incompatible change now.

> Current Practice:
> 
> VAX LISP treats FUNCTION declarations as describing only function bindings.

I'm not quite sure which you mean; do you mean it only supports the 
(FUNCTION name argtypes valtypes) form?  The Explorer only supports this
one.

> Cost to Users:
> 
> Existing uses of the FUNCTION declaration for function bindings will need
> to be changed to FTYPE declarations.  Such code could not have been portable,
> though.

That last sentence is not true, since CLtL clearly says that it is allowed
and defines what it means, so no valid implementation can disallow it.