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

["Robert I. Eachus" <rieachus@comcast.net>]

Marin David Condic wrote:

> How about *adding* something to system like:
> 
>     System.Compiler_ID : constant String := "Something Useful Here" ;
> 
> This would not break anything that was already using System_Name 
> (although given its general uselessness, I doubt that is very much) and 
> would provide a mechanism for identifying the compiler that is doing the 
> job. Then statements like "if (Compiler_ID = "Something") then..." would 
> possibly be useful.

In Ada 83 that wouldn't have worked.  But I think it would be wonderful 
to get rid of the type Name in system and add three string constants:

Operating_System:      constant String := implementation_dependent;
Hardware_Architecture: constant String := implementation_dependent;
Compiler:              constant String := implementation_dependent;
Version:               constant String := implementation_dependent;

If I were going to write this up as an AI, I would include as 
"Implementation Advice" that the strings be static, that configuration 
pragmas be allowed to affect the values, and that the version strings 
for a particular compiler should sort as strings into cronological order.

Oh, and redefine System_Name to return a String, but not necessarily a 
static String.  It should give the name of the machine the program is 
running on.  (The machine I am typing this on is Milliways.) Memory_Size 
should be redefined as a function that returns the system memory size, 
and there should be a functions Stack_Size and Heap_Size that return the 
actual maximum permitted Stack_Size (either for the main program or for 
the task where it is called), any the size of the default heap.  (The 
more I think about it, the type they return is not a stumbling block. 
That should be an implementation defined integer or modular type. Any 
program that needs to use the type will either use numberic literals or 
do a type conversion.)

Anyone interested enough to propose this as a (late) addition to Ada0Y? 
  Since Jean Ichbiah interchanged Name and System_Name at the very last 
moment in Ada 83, there certainly is a precedent for changing System 
late in the game. As far as I know that was the only significant change 
between the printers proof and the published ANSI standard.  (Page 
number 2-2 certainly wasn't significant. ;-)

> You still need some mechanism to wrap that around declarations and other 
> stuff. Perhaps that could be solved with some flavor of a pragma that 
> could take a case-like if statement around what you want conditionally 
> compiled. Maybe the whole thing should be solved with a pragma since you 
> don't want to have to first "with" System before you can start 
> conditionally withing other packages. That also gets simpler to deal 
> with from a language perspective since there has always been the ability 
> to have implementation defined pragmas.

My current approach to this problem is to have packages OS, and ISA. 
Then in whatever library I am working these do the necesssary via 
package renames.  I've thought about using a preprocessor, but so far 
the renames work and look much neater, as far as the source code is 
concerned.  What I would really, really like is for the compiler to 
expand those names based on compile time flags and defaults.  I don't 
think that trick should be a language defined/required behavior, but I 
don't see any reason why a compiler couldn't validate even if it 
included such a feature.


-- 
                                           Robert I. Eachus

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