Re: Compile time executed functions

[Florian Weimer <fw@deneb.enyo.de>]

Ted Dennison<dennison@telepath.com> writes:

> >Yes, but this way, values can be computed prior to run time which
> >appear to be constants (even during compile time) but are in fact not.
> 
> Ahhh. But that's not what he was talking about. He wants to be able
> to supply some arbitrary function (like say an integrator or a
> matrix math routine or a search routine) which the compiler will
> then run during the compile phase, find the value of the result (eg:
> 3.57) and then place that value in a constant which he can have the
> compiler stick in the ROM section of the generated code. In order to
> stick a value in the ROM section, it clearly cannot be computed at
> runtime.

Why not?  You can do this certainly with FORTH: you run the system in
'compile mode', and just before starting the actual execution, you
dump the entire environment.  From the dump, a ROM image can be built;
and there's no need to copy constants from ROM to RAM during
initialization.  (I think this works with some Lisp dialects as well,
Emacs is probably an example.)

> I'd claim that most developers will not accept the responsibility of
> an X(1) compiler,

Why not?  There are already some programming languages where you have
to some discipline not to write constructs which exhaust compile-time
ressources (C++ comes to my mind, and the problem with C++ is nottime
spent compiling, but the amount of core memory used).