Re: Are library names data or syntax?

["Marc Nieper-Wißkirchen" <marc@nieper-wisskirchen.de>]

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Am Mo., 22. Juli 2024 um 20:47 Uhr schrieb Maxime Devos <
maximedevos@telenet.be>:

> > [...]
>
> >
>
> >In what kind of situation might a library name be made up of identifiers
> (syntax objects) that might need to carry lexical information?
>
>
>
> As implied by the previous: never (in Guile, and probably most others).
>
>
>
> The only exception I can think of, is if:
>
>
>
> * ‘define-library’/’library’ is implemented as a macro (this is not part
> of RnRS, but AFAIK neither is it against the standard)
>
> * hence, you can define a module from within another module (might be
> situationally useful, but comes with new difficulties for module lookup)
>
> * there are multiple module namespaces
>
> * to determine which module namespace to put the module in,
> ‘define-library’ uses lexical information
>
> * in particular, it uses components of the name of the library for lexical
> information, even though there are other options like using the _*whole*_
> name (i.e., (foo bar) itself instead of ‘foo’ or ‘bar’).
>
>
>
> That’s a lot of ifs, and even then identifiers aren’t necessary, since
> (AFAIK) the name (foo bar) itself carries lexical information (not sure).
>
>
>
> I’ve been assuming that numbers (in syntax) (say, #'3) don’t carry lexical
> info, but since ‘syntax numbers’ carry file name+position information, it’s
> not much of a stretch to potentially also include lexical information, so
> perhaps numbers would work just fine too! (Implementation-dependent, but
> ‘multiple module namespaces’ and ‘define-library as a macro’ are also
> implementation-dependent.)
>

This would need a redefinition of what a syntax object is (see the R6RS).
In principle, this would be possible, but the result would be incompatible
with the R6RS. In R6RS, a macro transformer is allowed to output raw
numbers; this would not be allowed in a hypothetical Scheme version that
assumes that numbers necessarily carry a wrap (as identifiers do in the
R6RS).

Source location information is not mandatory information for the expander,
so this reasoning does not apply here.

Marc

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