[Lazarus] Parser

[Michael Van Canneyt]

On Thu, 1 Jul 2010, Hans-Peter Diettrich wrote:

> Michael Van Canneyt schrieb:
>
>>> ... because it increases the maintainance work on fpc. Even with one
>>> front end only we are almost unable to keep the issue count under
>>> control. I'am pretty sure that more front ends will be rejected without
>>> more people working on bug fixing in fpc.
>> 
>> Exactly. We can barely cope as it is. If we compiled C as well, we'd get 
>> bug reports about glibc or whatever C library fails to compile.
>
> I've already translated a couple of available C libraries into Pascal, using 
> ToPas. There exist only a few constructs that do not translate into Pascal 
> directly (bitfields...), but their addition to the compiler (code generators) 
> should not be a problem - in the easiest case they can be emulated in pure 
> OPL, not affecting the code generators at all. At statement and procedure 
> level most languages don't differ much, and FPC even has the C operators 
> already implemented. Since the ToPas C parser is written in OPL, its 
> adaptation should be easy. This may become my next project, after the 
> parser...

You are missing the point. The point is not DOING it. the point is the
support afterwards. After 15 years of FPC support, I have some experience.
Even now, bugs creep up that are seemingly SO basic:
W : word;
begin
   w:=0;
   for i:=0 to pred(w) do // What to do ?
end;

The compiler's behaviour is different from Delphi. This is a bug, we must
deal with it. After 15 years. So, if the compiler produces different code
in some C library, then we'll have to deal with it. People will report it.
So no, thank you.

And frankly, I would not use topas as a reference. I tried it on some - to
my taste - simple C code and it failed horribly. I was unable to solve it, 
also because it lacks all documentation. This is not the kind of standard 
I would like to see in FPC.

So I'd say that you already failed on something more simple than FPC
compiling all languages. First get topas to convert all C code out 
there without a glitch, then we'll talk again.

Do not get me wrong: I think topas is a technically nice product. I admire
that you can write the code to do it, to make it work (more or less). That is
not the point; The point is that writing the code is actually the least of
the problems. It's what comes afterwards.

>
>> And, frankly, the project is called "Free Pascal" for a simple reason: it 
>> is a *Pascal* compiler and a *Pascal* project.
>
> Microsoft started with a couple of compilers, until they implemented a common 
> back-end for all "Visual" languages, and later they invented the CLR. gcc 
> also allows to add FEs for a certain class of languages, so why should FPC 
> not become another Free Portable Compiler?

Because Microsoft has 1500 people, GCC has several companies behind it.
FPC has 4 people technically savvy in compiler matters.

>
> I wonder how somebody can say "it's hard to do", without having even tried 
> ;-)

I didn't say it is hard. I say that the support for it would kill us and the
project.

This is the problem of most open source out there:  Enthousiasts write
it. And then the good is separated from the bad: supporting it for many 
years. Patiently fixing all bugs. And there will be lots.

FPC existed before the term 'Open Source' existed.  That means something.

Michael.