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From: ddb@mrvax.DEC (DAVID DYER-BENNET MRO1-2/L14 DTN 231-4076)
Newsgroups: net.lang.c
Subject: "Funny" names in programs
Message-ID: <248@decwrl.UUCP>
Date: Thu, 17-Jan-85 15:00:43 EST
Article-I.D.: decwrl.248
Posted: Thu Jan 17 15:00:43 1985
Date-Received: Thu, 24-Jan-85 08:30:11 EST
Sender: daemon@decwrl.UUCP
Organization: DEC Engineering Network
Lines: 58

Of course (:-), BLISS has had a cleaner way to handle this for some
time:  it has a lexical function %name(), which causes its string
argument to be treated as a name regardless of the normal naming rules.
This can be buried in a macro to make references to these funny
variables look normal.

BLISS has a lot of other useful lexical functions also.  In fact it
makes the C pre-processor look pretty dull by comparison.  Consider:

%charcount(string)		Number of characters in string
%string(string,string,...,string) Single quoted string from many
%explode(string)		comma-separated list of single-char strings
%identical(arg,arg)		True if both args exactly same
%isstring(arg)			rue i
				True if string literal
%ctce(arg)			True if arg is compile-time constant expr.
%ltce(arg)			True if arg is link-time constant expr.
%nbits(ctce,ctce...)		Max number of bits needed to represent
				numerically largest arg in signed field
%nbitsu(ctce,ctce,...)		Same, unsigned field
%declared(name)			True if name is declared in current scope
%error(string)			Cause compiler to issue string as error
%quote				Inhibits lexical binding of the lexeme
				following
%unquote			Forces lexical binding of the lexeme
				following
		These last two are really amusing, not to mention useful;
		Like writing macros which, when expanded, redeclare
		themselves, or writing macros which expand other
		macros in their body at declaration time instead of
		at expansion time, or passing names of macros as arguments
		to other macros, or....  If you need either of these,
		there's no substitute.
%remaining			comma-separated list of actual parameters
				to macro-expansion currently being processed
				which aren't assigned to formal parameters.
				This makes expandable-tail argument lists
				to pass to a lower level trivial to
				implement.
%length				number of actual parameters in call

etc. etc., lots more.  %bpval is the number of bits per fullword
value (think int).  %bpunit is the number of bits per addressable unit.
%bpaddr is the number of bits in the address of an addressable unit.
%upval is the number of addressable units per fulword value.  

It was fairly easy to write code that ran on VAXen (8-bit byte oriented)
and PDP-10 (36-bit word oriented) system using bliss.  The particular
code took a bit-stream representation of some binary data as it had
existed in the memory of one kind of system, and extracted fields from
it (converting them to binary formats understood by the current system)
(you had to tell it where the field had been on the original system).
(This was the data conversion part of DECs Data Interchange Library
produce
product).

		-- David Dyer-Bennet
		-- ...decwrl!dec-rhea!dec-mrvax!ddb