[9fans] C, APE, Posix

[C H Forsyth <forsyth@vitanuova.com>]

>network protocol standards (IL not withstanding), but it _did_ choose to fight
>the POSIX/C99 et. al battle.

there are several different aspects to this:
1. the language accepted by the C compiler excluding the preprocessor and #include files
2. the C standard's include files
3. POSIX interface

for (1), there are Plan 9-specific extensions (but then, there are gcc-specific extensions).
more dramatically, Plan 9's compiler has its own simple pre-processor. i think it has
helped keep the source tree relatively free of the horrible mess that cunning or clumsy
use of the C preprocessor has made of other trees.

i don't think there is currently a deliberate intent not to implement the basic C language
as described in the standard. there are one or two significant differences. notably the
compiler doesn't implement the value-preserving rules for comparisons. the rules in
standard C are fairly awful (i'm thinking particularly of the dependency on the size of values).
instead the compiler implements the older unsigned-preserving rule, if it implements
any particular rule. still, the main reason not to implement value-preserving isn't
aesthetic, but lack of time or effort on the one hand, and a slight worry that an
explicitly `silent change' in C language semantics might break existing code in subtle ways.
since most of the code has been compiled by other compilers, probably there wouldn't
be a big problem, and the work, which is finite, should be done for completeness.

for (2), one advantage of the Plan 9 #interface to libraries
is that the #include structure is straightforward and reasonable
(in the sense that one can reason about it). generally for one library (in particular
the C library <libc.h>) there's one #include that must be included.
declarations appear in exactly one #include file.
the machine-dependent and machine-independent declarations are handled cleanly.
none of those statements apply to ANSI C's stdlib/stddef/.../.../... mess.

for (2) and (3), to allow programs to be imported, there's the APE environment,
including (for (1)) options and commands to provide an ANSI-compatible C preprocessor.
the usual reason that programs are hard to import (apart from ./configure,
which doesn't actually do what it says), is that they are not ANSI/POSIX programs
but (typically) gcc programs.

so actually the problem is not that Plan 9 has an
aversion to ANSI/POSIX but that everyone else has, differently, and as far
as (1) goes, the source code is sometimes full of extensions and special attributes.
perhaps they should consider standardisation?