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From: Paul Graham <pgraham@cadence.com>
Subject: Re: Language Lawyer question
Date: 2000/06/02
Message-ID: <39381943.88350E6@cadence.com>#1/1
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Date: 2000-06-02T00:00:00+00:00
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Wes Groleau wrote: 
>    Why do we have to write
>       Some_Type'Pred (Some_Value)
>    when
>       Some_Value'Pred
>    is more natural/intuitive and
>    carries just as much type info?
> 
> I pointed out that there is no type info in a literal (like
> Orange'Pred) but he said that the type info would be somewhere
> else in the statement.  I could not quickly come up with a
> counter-example. Plus, how often would we use a literal as
> parameter to 'Pred ?  Might as well just use the literal value 
> of the Predecessor.

It could be Some_Type'Pred(f(x)) for an arbitrary function f (this has
the same problem as your example using a literal, but is more realistic.

Or you might want to say Integer'Pred(1+1), which is easier to parse
than (1+1)'Pred.

An attribute like 'Pred has a kind of qualified expression syntax, if
you think of Pred as an overloaded function predefined on all discrete
types.  Then the type qualifier Some_Type' resolves the overloading.

Paul