Encoding library names

[Lassi Kortela]

>  > In R7RS non-negative integers can be library name parts. Since these
> library names look natural, it would be good to backport this to R6RS
> implementations.
>
> Then (library [...] (import (srfi 1)) [...]) would work, and since 
> ‘library’ is (R6RS) standard and reasonably portable it would then 
> appear that (srfi 1) is (R6RS) standard and portable, whereas it isn’t 
> R6RS, and hence not a good idea to backport.

For the time being, (library ...) is only available in R6RS 
implementations. But the next report (tentatively titled R7RS-large) is 
on track to be a merger of R6RS and R7RS, and hence will most likely 
support both (library ...) and (define-library ...) while merging their 
semantics in some way.

I would agree that interop between strict R6RS and other dialects of 
Scheme is important. To that end, the option to use numbers in R6RS 
library names using the : prefix is good to have. (R6RS does not have 
the vertical bar notation |123| to turn numbers into symbols, so strict 
R6RS code cannot even rely on that notation to encode numerical library 
name parts).

A further complication is that :123 is a keyword in some Scheme 
implementations. (This syntax comes from Common Lisp and Emacs Lisp, 
perhaps going as far back as Maclisp.) It might be best if any leading 
colon in a library name part is simply removed.

> > The colon causes endless grief when mapping library names to file names.
> > For example, look at all the %3a in
> > https://github.com/arcfide/chez-srfi. That's not even the worst of it.
>
> I don’t think this is a problem for Guile? I don’t recall to what 
> extent, but (srfi ...) modules are somewhat special-cased in Guile (or 
> maybe it was integers in general for define-library) – maybe its 
> implementation of define-library translates (srfi 1) to (srfi srfi-1) (I 
> don’t recall the specifics). Hence, the file can simply be named 
> “srfi/srfi-1.scm”.
>
> For compatibility, both(**) (srfi srfi-N) (ß non-standard Guile thingie) 
> and (srfi :N) need to be supported anyway for ‘define-module’ (ß 
> Guile-specific interface), so which of them determines the file name is 
> just a matter of convenience.
>
> Also, AFAIK that %3a encoding isn’t necessary (and neither 
> recognised(^)) in Guile – I don’t think Guile does any percent 
> encoding(*). I think naming the file “srfi/:1.scm” would work fine, 
> although it’s not something I’ve tried before. (There might be a problem 
> with Makefile if ‘make’ doesn’t like the :, but I have some ideas for 
> simple ways around that.)

Guile should support non-negative integers in any library name, not only 
for the SRFI libraries. R7RS allows them anywhere.

I would recommend implementing the %-encoding of arbitrary UTF-8 bytes 
(several Scheme implementations do it when translating library names to 
file names) but to avoid using it in practice.

The : prefixes should be stripped before encoding a library name as a 
file name.

FAT, NTFS (and probably other file systems) do not allow colons in file 
names. I am not aware of any file system that forbids the percent sign.

> (*) implication: you can’t have two different modules (foo/bar) and (foo 
> bar) in Guile.

Percent-encoding the slash solves this easily.

> (^) (srfi %3a1) would mean the module has literally (srfi %3a1) as name.

AFAIK that is allowed by RnRS.