-*- Text -*-

This is a first ***draft*** of a description of what symbols should be
present in CL:*FEATURES* for various platforms.  A possible future
direction of this documentation might be a CDR document, if it turns
out to be a good idea.  (Making the language of this document much
more precise will be necessary then.)

We will start by limiting ourselves to OS, CPU and endianness features
on Windows and POSIX platforms.

There are various possible implementation strategies ranging from null
implementations (when the host Lisp already pushes the wanted feature)
to using FFI (e.g. calling uname() to grab system information.


=============
Specification

* ENDIANNESS

Either :LITTLE-ENDIAN or :BIG-ENDIAN should present in *FEATURES*.
For the time being, we will not concern ourselves with other
orderings, switchable endianness, etc.


* OPERATING SYSTEM

On Windows, :WINDOWS should be present in *FEATURES*.

On POSIX systems, the "sysname" information from uname(3) should be
used to push the appropriate symbol to *FEATURES* by upcasing that
string (or downcasing for the "modern" lisps) and interning it in the
keyword package.

Examples:

  :DARWIN
  :LINUX
  :NETBSD
  :OPENBSD
  :FREEBSD

For convenience, :UNIX should be pushed when running on
POSIX/UNIX-like operating system (that doesn't include Windows) and
:BSD should be present when running on BSD-based systems (that
includes Darwin)

[add :MACH too?]


* CPU

These features should be mutually exclusive:

  :X86
  :X86-64
  :PPC
  :PPC64
  :MIPS
  :ALPHA
  :SPARC
  :SPARC64
  :HPPA
  :HPPA64

[add more ...]

[note: it's debatable whether :X86 shouldn't also be exported on
x86-64, and :PPC on ppc64.  SBCL doesn't.  Other ways
to handle, for example, the x86/x86-64 case would be to export
something like :PC386 in both cases or have an additional :X86-32. Or
finally, have just :X86, :PPC, etc, and add :32-BIT-CPU and
:64-BIT-CPU features.]


=======================
Unreferenced References

  "CLHS: Variable *FEATURES*"
  <http://www.lispworks.com/documentation/HyperSpec/Body/v_featur.htm>

  "Maintaining Portable Lisp Programs", by Christophe Rhodes
  <http://www-jcsu.jesus.cam.ac.uk/~csr21/papers/features.pdf>
