Re: Is it really Ok to assert that the Ada syntax is a context-free grammar ?

[Robert A Duff <bobduff@shell01.TheWorld.com>]

Hibou57 <yannick_duchene@yahoo.fr> writes:

> On 20 f�v, 11:34, Ludovic Brenta <ludo...@ludovic-brenta.org> wrote:
>> Jeffrey is correct; it is not a "type cast", it is a "type conversion"
>> and there is no such thing as "Ada.Unchecked_Cast". Yes, this is nit-
>> picking; why would we choose Ada if we didn't care about details and
>> wording?
>
> Ok, forgive me for the english mistake : I use either type cast or
> type conversion to mean the same thing. I will take care in the futur.

I think there's nothing wrong with using informal terms when talking
about Ada, so long as the meaning is clear from context.  For example,
I sometimes use "pointer" to mean "access type" or "access value", and I
don't see anything wrong with that.  (And some Ada folks lecture me
about it.  ;-))

The problem with "type cast" is that in the Ada context, it could mean
two different things -- a type_conversion (which is well-defined
according to the high-level semantics) or an "unchecked conversion"
(i.e. an instance of Ada.Unchecked_Conversion, which is defined
in terms of bit-level representation).  The difference is important!

> But I'm still not sure about the assertion that it is context free
> (while, Ok, the AEM does not tell it is LR(1))

The grammar given in the Ada RM under "Syntax" is a context free
grammar.  It is, however, ambiguous, and therefore not LR(1).

You noted the biggest ambiguity -- X(Y) could mean various things.
There are a few others (e.g. .all can be implicit in some cases, and
subprogram calls with no parameters don't get empty parens).  The full
power of semantic analysis is required to disambiguate these things, in
the general case.

- Bob