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Date: Sat, 23 Feb 2008 13:27:18 +0100
From: Georg Bauhaus <rm.tsoh.plus-bug.bauhaus@maps.futureapps.de>
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Newsgroups: comp.lang.ada
Subject: Re: Separate Compilation in Programming Languages
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Date: 2008-02-23T13:27:18+01:00
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adaworks@sbcglobal.net wrote:
> "Niklas Holsti" <niklas.holsti@tidorum.invalid> wrote in message 
> news:47bf11df$0$14990$4f793bc4@news.tdc.fi...
>> adaworks@sbcglobal.net wrote:
>>
>>> Do you still use the "is separate" feature in a package body?
>> I never use it. My subprograms are rarely long enough to make it useful (given 
>> that there is no compilation-speed advantage under GNAT), and I seldom use 
>> nested packages.
>>
> Thanks.  The issue is not compilation speed, nor even size of the
> source code.   Rather, the real benefit of Ada's separate compilation
> model is the management of dependencies. 

I like separate subprograms or separate package bodies not only
because of dependency management, but also because they allow a
kind of source code organization not available without separation.
It is about distraction and separation of concerns.

Given that Ada has nesting, I can make all things local to where
they are used. Much like I can do using FPLs' let expressions
(as in Scheme or ML) or where clauses (as in Haskell).
But I don't have to "clutter the listing" between "is" and "begin"
with full implementation details that only disturb linear reading.

It's like saying, "I'll leave the details out for the moment",
or, "I'll talk about the implementation later". Still the
subp profile or package interface have been mentioned. That is,
the reader has enough information in order to follow the program
text.


function sqrt_iter(guess, x: Number) return Number is

   function improve(guessed: Number) return Number is separate;
   -- another number approximating sqrt_iter'Result

   function good_enough(guessed: Number) return Boolean is
   begin
      return abs (guessed * guessed - x) < 0.001;
   end;

begin -- sqrt_iter
   if good_enough(guess) then
      return guess;
   else
      return sqrt_iter(improve(guess), x);
   end if;
end sqrt_iter;