On 29/12/11 22:05, R A wrote:
The gcc developers, and everyone else involved in the development
of C as a language, are perhaps not superhuman - but I suspect
their combined knowledge, experience and programming ability
outweighs yours.
given. but do you have a consensus of the community that this feature
is not worth including? i haven't even heard but from a few people
saying that "it's not worth it because if it was, 'we're the ones to
have thought about it'".
computing science (may i call it a science??), is all about
objectivity and examining the theories and evidence. it should be
prepared re-examine everything when a new idea is introduced or
challenged.
so if it's a bad idea, explain to me exactly why; not go about human
politics.
I don't speak for the gcc community - either for the users or the
developers. But occasionally I can help out on this mailing list, and
let the real developers get on with their work.
There are a number of reasons why you wouldn't want an evaluation system
as part of the C preprocessor (disregarding any thoughts about it being
hard to do, impossible to standardise, and redundant given all the other
ways to achieve the same ends).
There is no standard environment for C. Should calculations be done as
32-bit integer? What about targets that use 16-bit integers (or even
64-bit integers)? You want to call the function "eval" - what about
existing code that uses the word "eval", either as a pre-processor macro
or as part of the C code? You want to allow recursive macros - that
opens a wide range of problems for getting consistency and clear
definitions (and typically requires being able to define macros in at
least two different ways - one recursive, one literal). You want to
allow the evaluation of symbols and expressions by the preprocessor -
that means it has to understand the syntax and semantics of these
expressions, rather than just doing simple text manipulation. And it
leads to more questions when macros and expressions are mixed - when do
you do "evaluation", and when do you do simple text expansion? How do
you write macros that have the "eval" function in them?
I don't expect or want any answers here - I don't think anybody is
looking for a discussion aiming to implement the eval idea. I just want
to point out that there are many, many questions involved here before
anyone could even think about implementing it. And I don't think they
could be resolved in a way that is consistent, practical, and adds
anything to C or the C pre-processor that is not better handled by an
external code generator or an independent macro language. No one wants
to re-invent the wheel.
