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Date: 27 Apr 92 15:58:47 GMT
From: yale.edu!spool.mu.edu!umn.edu!sctc.com!stachour@yale-bulldog.arpa  (Paul 
Stachour)
Subject: Re: Procedure/function specification/declarations
Message-ID: <1992Apr27.155847.5333@sctc.com>
List-Id: <comp.lang.ada>

svh@verdix.com (Steven Hovater) writes:

>In article <21295@hacgate.UUCP> hayes%bh_ddemo3@hac2arpa.hac.com writes:
>>I'm a beginner to Ada...
>>
>>
>>I've noticed that it is possible to specify a procedure 
>>or function without parameters without using a 
>>null parameter list specification.  What was the thinking
>>behind this or why is this method superior?
>>
>>For example, in ANSI C a function prototype might be
>>   boolean empty (void);
>>In Ada, a corresponding specification would be
>>   function empty return boolean;
>>

  I think that the C style comes from the PL/I style.
I don't know where PL/I got the style.

  The need is to distinguish between passing a function
and calling a function.  For exmple, if I write in PL/I,
  [My PL/I is rusty, this might not be 100% right]

      DCL EMPTY_F ENTRY () RETUNRS ( ENTRY () );

and then call P, which expects to take as its first argument
a entry with no parameters, then I need to distinguish between

  1:    A = P ( EMPTY_F(), ... )
and
  2:    A = P ( EMPTY_F, ... )

In case 1, the function returned by EMPTY_F is being passed,
in case 2, EMPTY_F is being passed.

Note that any well-defined language that allows entries to be passed
as arguments needs some way of making that distinction. [No, I don't
consider C as a well-defined language, but C does allow entries
to be passed as arguments and Ada doesn't.  That's good in some
contexts and bad in others.  It's my opinion that the requirements
for Ada forbid the definition of entries being passed as arguments
based upon the horrors that were present in FORTRAN and Assembly and
... code of that day; these horrors are often also present in
poorly-designed C programs.  They are not present in poorly designed
Ada programs because they aren't possible.]


-- 
Paul Stachour          SCTC, 1210 West County Rd E, Suite 100           
stachour@sctc.com          Arden Hills, MN  55112-3739
                             [1]-(612) 482-7467