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From: Georg Bauhaus <sb463ba@d2-hrz.uni-duisburg.de>
Newsgroups: comp.lang.ada
Subject: Re: Ideas for Ada 200X
Date: Mon, 16 Jun 2003 16:19:24 +0000 (UTC)
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Bill Findlay <yaldnifw@blueyonder.co.uk> wrote:
: 
: shiftTally(shift)(dayOfWeek(month).tallyIndex).sortTally(s).nbRejects :=
:   idem + 1;

Hm. How about renaming and access values?
The following two examples of ad hoc code have given me the
effect of idem.

procedure waiter is

   b: Bill;
begin

   add(b, Soup);
   add(b, Chicken);
   declare
      use type  Prices.Amount;

      p: constant Bill_item := item_at(sort(b), 2);
	-- this would be your long LHS.

   begin
      p.all := p.all + 1.20;  -- only one call on item_at here
   end;

   add(b, Rice);


end waiter;

There is only one call on sort before the left hand side
gets its new value.

	call bills__add
	movl %eax,%ebx
	pushl $2
	pushl %ebx
	call bills__sort
	addl $4,%esp
	pushl %eax
	call bills__item_at
	addw $153,(%eax)
	pushl $4
	pushl %ebx
	call bills__add


Similarly, given a complex data structure, and
some functions for indexing the data structures,

   type Arrow is access all Point;
   type Point_list is array(List_index) of Arrow;

   function make_one return Point_list;
   function rand return List_index;

then from

begin
with_renaming:
    declare
       p: Arrow renames make_one(rand);
    begin
       p.x := p.x + 333;
    end with_renaming;

without_renaming:
    begin
       make_one(rand).x := make_one(rand).x + 555;
    end without_renaming;
end big;

I get a total of 3 calls to make_one and rand, one of
each in the with_renaming block, two of each in the
other block, without renaming.


-- Georg