Re: Standard Ada Preprocessor (Was: why ada is so unpopular ?)

[Jacob Sparre Andersen <sparre@nbi.dk>]

Marin David Condic wrote:

> Yeah. Isolating them down at some low level is fine. But that still
> leaves you with the problem of "How do I code up the stuff at the
> low level?" You're either controlling it with some kind of build
> scripts & CM or you do it with something inside the language. Given
> that it needs to be done & I can't keep pushing it off with
> indirection forever, I'd like a language mechanism for doing it.

Would a pragma in the package specification declaring which file the
package body should be read from depending on some compilation
parameters (compiler, operating system, etc.) do the job?

Something like this, where the body is grabbed from the file named by
the first "Body_Source_File" pragma with a matching condition.  If no
"Body_Source_File" pragma has a matching condition, the compiler just
uses its default routine for finding the source code for the package
body.

with System;
with System.Compiler_Flags;

package Hiding_Compiler_Specific_Details is
   pragma Body_Source_File
     (Condition => System.Compiler_Name = "GNAT",
      File      => "GNAT/HCSD.ada_body");
   pragma Body_Source_File
     (Condition => System.Compiler_Flags.Set ("--with-gnu-gettext"),
      File      => "GNU-Gettext/HCSD.ada_body");
   pragma Body_Source_File
     (Condition => True,
      File      => "default_implementations/HCSD.ada_body");

   ...
end Hiding_Compiler_Specific_Details;

This would limit the language handling of conditional compilation to
selecting package/unit bodies, but I think it would solve most of the
problems mentioned in this discussion, without risking the whole
preprocessing hell seen in too many C programs.

Greetings,

Jacob
-- 
�But you have to be a bit wary of a ship that collects
 snowflakes.�                                  -- Diziet Sma