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From: Nick Roberts <nick.roberts@acm.org>
Newsgroups: comp.lang.ada
Subject: Re: idem (Was: += in ada)
Date: Fri, 31 Oct 2003 22:40:07 +0000
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Date: 2003-10-31T22:40:07+00:00
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Jacob Sparre Andersen wrote:

> Preben Randhol wrote:
> 
>> The problem I have with idem is that it looks like just another
>> variable.
> 
> Yes.  But it is a cool idea.  And with a suitable idem marker, I think
> it would make it possible to write even more readable code.  Also,
> "idem" doesn't look any more like another variable than the operators
> "and", "or" and "not".
> 
> What I worry most about with idem is that it would make the expression
> syntax used in assignments different from that used in other places.

What if we only changed the syntax of the assignment statement?

Change RM95 5.2(2) to:

    assignment_statement ::=
       explicit_assignment_statement
     | implicit_assignment_statement

    explicit_assignment_statement ::=
       variable_name := expression;

    implicit_assignment_statement ::=
       variable_name :=
          ALL binary_adding_operator term
          {binary_adding_operator term};

I've used the reserved word 'all' here, since I think it serves the purpose 
and saves introducing a new reserved word.

This formulation adds some complexity to the definition of the assignment 
statement in the RM, but it avoids changing expressions in any way. Just a 
thought.

-- 
Nick Roberts