🚀 go-pugleaf

In article <1993Jan19.180718.3482@csqx.cs.rhbnc.ac.uk> [which hasn't
arrived here yet], andreww@cscx.cs.rhbnc.ac.uk (Andrew Waters) writes:
> Is this truely more logical?  Look at the example:
> 
> #define echo(a) { a ; x }
> #define x       2 * x
> echo (x)
> 
> As before the macro argument "x" is replaced giving the replacement list
> 
> { 2 * x ; x }
> 
> We now examine this replacement list for further macro expansion.  "x" is no
> longer available for replacement,  giving the final result
> 
> { 2 * x ; x }

No.  The rule in the standard about nonreplacable macro names says:

	These nonreplaced macro name preprocessing tokens are no longer
	available for further replacement...

Note carefully that it's talking about the individual preprocessing
tokens, not the macro in general.  Thus, when "x" is expanded to "2 * x"
in the above example, the "x" in the replacement string is not replaced
and *that particular token* is marked unavailable for further
replacement, not the macro x.  Thus, when "{ 2 * x ; x }" is rescanned,
the first "x" would be replacable, but it has been marked and so is left
alone.  The second "x" has not been marked, so it is replaced normally
giving "{ 2 * x ; 2 * x }".  Now the second "x" has also been marked so
that if this string is later rescanned neither "x" will be replaced
again.
----
Larry Jones, SDRC, 2000 Eastman Dr., Milford, OH  45150-2789  513-576-2070
larry.jones@sdrc.com
It doesn't have a moral, does it?  I hate being told how to live my life.
-- Calvin