[r6rs-discuss] What's up with the library names?
ludovic.courtes at laas.fr
Thu May 24 13:57:38 EDT 2007
Abdulaziz Ghuloum <aghuloum at cs.indiana.edu> writes:
> Right. And since it's far more convenient to write (rnrs)
> than it is to write (rnrs (6)), people are going to do that
> by default (I would). Next thing that happens is that r7rs
> comes out and any library you download would have an import
> of (rnrs) which says nothing about what they target. So,
> you start the trial and error process (which is what r6rs
> libraries were supposed to handle automatically). If, on
> the other hand, a library imports (r6rs) and your system
> complains about "(r6rs) library not found", then you would
> at least get a clue about where to look. And if you do
> change the import from (r6rs) to (r7rs), you would at least
> do that with caution instead of having your import bomb by
> being automatically upgraded.
Symbol versioning as implemented by the GNU linker  may be a valuable
source of inspiration. At link-time, a program is explicitly linked
against a specific version of each shared library depended on. Thus,
the resulting executable contains the expected version of each of the
symbols it imports:
$ objdump -T `which ls` | head
/bin/ls: file format elf32-powerpc
DYNAMIC SYMBOL TABLE:
100265f8 DF *UND* 00000010 GLIBC_2.0 readlink
10026600 DF *UND* 0000016c GLIBC_2.0 getgrnam
10012304 g DF .text 0000003c Base _restgpr_18
10026608 DF *UND* 00000054 GLIBC_2.2 __fpending
At run-time, the loader checks whether the requested symbol/version
combinations are provided by some shared library and bails out if not.
It is up to the library implementor to change the version of a symbol
when its binary interface is changed.
The analogy with R6RS libraries would be that, at the source-level,
Scheme programs would systematically specify the version of each
required library (including the standard libraries). The Scheme
compiler/linker/interpreter would then return an error whenever one of
the dependencies is not satisfied.
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