[Oberon] Clarifying type compatibility in Oberon-07

[Andreas Pirklbauer]

EDIT: Except of course that in the case of the definition of “equal types” Ta and Tb are *open* array types.


> On 05 Oct 2017, at 10:58, Andreas Pirklbauer <andreas_pirklbauer at yahoo.com> wrote:
> 
> > On Wed Oct 4 08:37:50 CEST 2017 August Karlstrom wrote: 
> > Oberon-2 has the following definition of *same type* in appendix A in 
> > the language report:
> >
> > Two variables a and b with types Ta and Tb are of the same type if
> > 1. Ta and Tb are both denoted by the same type identifier, or
> > 2. Ta is declared to equal Tb in a type declaration of the form Ta = Tb, or
> > 3. a and b appear in the same identifier list in a variable, record 
> > field, or formal parameter declaration and are not open arrays.
> >
> > As far as I understand, Oberon-07 uses structural equivalence for array 
> > and procedure types so we must add two paragraphs to this list:
> >
> > 4. Ta and Tb are array types whose element types and lengths are the same, or
> > 5. Ta and Tb are procedure types whose formal parameter lists match.
> 
> These two sentences are actually part of the definition of “Equal types”:
> 
> Equal types
> Two types Ta and Tb are equal if
> 
> 1.  Ta and Tb are the same type,  or
> 2.  Ta and Tb are open array types with equal element types, or
> 3.  Ta and Tb are procedure types whose formal parameter lists match.
> 
> -AP
> 

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