From: Ludovic Courtes
Date: Thu, 14 Jun 2007 10:00:40 +0200
Subject: [Formal] Versioned names for base libraries considered harmful

Submitter:      Ludovic Courtes
Type of Issue:  Defect
Priority:       Major
Component:      Base Library
Report:         Revised^5.94 Report on the Algorithmic Language Scheme
Summary:        The `rnrs' versioned library names for the base library
                are considered harmful.

R5.93RS changed the identifiers of the base libraries from `(r6rs ...)'
to `(rnrs ... (6))', the last `(6)' being a version specifier.

This change was discussed on the `r6rs-discuss' list last month [0].
Arguments were given against this change.  The main reason this was
considered harmful is that programs and libraries that do not specify
which version of the base library is being imported would suddenly break
when the next version of the report is implemented.  Thus, programs
meant to be "future-proofs" are likely to always specify the version
number when importing base libraries, i.e., `(6)'.  Practically, this
makes little difference compared to typing `(r6rs ...)'.

Arguments in favor of base library versioning were given [1].  The main
argument is that it would provide R7RS editors more flexibility because
they could use the same library names when deemed appropriate.  However,
these comments fail to acknowledge important points that were raised
during the discussion, notably the fact that there is no reason for a
program to blindly import any version of the base libraries.

I suggest reverting this change or at least discussing the rationale
behind it.

Thanks,
Ludovic.

[0] http://lists.r6rs.org/pipermail/r6rs-discuss/2007-May/002332.html
[1] http://lists.r6rs.org/pipermail/r6rs-discuss/2007-May/002369.html


RESPONSE:

Two changes have been made to make the move to versioned standard
libraries more useful:

- The examples in the report no longer specify an explicit version,
  and programmers are encouraged to use unversioned references.

- Implementations are allowed (but not required) to permit the
  co-existence of different versions of the same library.