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From: phil.clayton@lineone.net
Newsgroups: comp.lang.ada
Subject: Re: Quantified expressions: no support for restriction predicates
Date: Sun, 29 Apr 2012 11:37:19 -0700 (PDT)
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Date: 2012-04-29T11:37:19-07:00
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On Sunday, April 29, 2012 3:03:50 PM UTC+1, Robert A Duff wrote:
> phil.c...@lineone.net writes:
> 
> > Drat.  I knew about the parentheses.  (Personally, I would have liked
> > parentheses to be required only when there is a syntactic ambiguity.
> > I suppose that is so often, you may as well have them all the time.)
> 
> Note that you don't need "extra" parentheses.
> You can say "F(for all ...)" instead of "F((for all ...))".

I also knew that but didn't choose my words very well :)


> > My thinking is that having a predicate to restrict the elements that
> > one is quantifying over (just like a subtype predicate restricts the
> > elements of a subtype) would avoid the need to work out the equivalent
> > logical expression, which differs depending on the quantifier - a
> > likely source of error.  So, while more syntax would be needed, this
> > should actually simplify quantification concepts.
> 
> Well, if you are willing to give a name to the subtype, you
> can put a Static_Predicate or Dynamic_Predicate aspect on it.
> Does that help?

Is that actually possible for a Dynamic_Predicate?  Section 3.2.4 Subtype Predicates, para 27/3 says:

  The discrete_subtype_definition of a loop_parameter_specification
  shall not denote ... or any subtype to which Dynamic_Predicate
  specifications apply.

Phil