Re: Language Lawyer question

[Paul Graham <pgraham@cadence.com>]

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