Ada95 BNF

Ada95 BNF

[Martin Dowie]

Looking through the BNF on AdaPower.com and the LRM that comes with
adaguide, I noticed
that package_unit_name is defined as a name, which in turn can be all sorts
of things,
including a 'name', which in turn can be lots of things - including a type
conversion?!

Shouldn't package_unit_name be defined as an Identifier?..

Re: Ada95 BNF

[Stephen Leake]

"Martin Dowie" <martin.dowie@nospam.baesystems.com> writes:

> Looking through the BNF on AdaPower.com and the LRM that comes with
> adaguide, I noticed
> that package_unit_name is defined as a name, which in turn can be all sorts
> of things,
> including a 'name', which in turn can be lots of things - including a type
> conversion?!

Just because something is allowed by the syntax, doesn't mean it is
allowed by the language. See the appropriate LRM section for the real
rules. In this case, 'parent_unit_name' is first discussed in 10.1.1,
which doesn't actually help that much.

> Shouldn't package_unit_name be defined as an Identifier?..

A 'parent_unit_name' can be of the form ancestor.parent, which is not
an "identifier". So "name" is appropriate.

-- 
-- Stephe

Re: Ada95 BNF

[Martin Dowie]

Ok... this seems a little strange to me - but if those are the rules! :-)

Is it really that hard to come up with a BNF that does actually match
what the language does allow?

"Stephen Leake" <stephen.a.leake.1@gsfc.nasa.gov> wrote in message
news:uk83yv1su.fsf@gsfc.nasa.gov...
> Just because something is allowed by the syntax, doesn't mean it is
> allowed by the language. See the appropriate LRM section for the real
> rules. In this case, 'parent_unit_name' is first discussed in 10.1.1,
> which doesn't actually help that much.
>
> > Shouldn't package_unit_name be defined as an Identifier?..
>
> A 'parent_unit_name' can be of the form ancestor.parent, which is not
> an "identifier". So "name" is appropriate.

Re: Ada95 BNF

[Christoph Grein]

The Ada BNF reflects a bit the parsing sequence. If something resolves to a name 
in the syntax, the name resolution rules have to be applied. This involves 
overloading resolution and a lot of other things.

Re: Ada95 BNF

[Marius Amado Alves]

> Is it really that hard to come up with a BNF that does actually match
> what the language does allow?

I thing that good thing happens with Pascal (I dont have the Report at
hand to be 100% sure).

-- 
Marius Amado Alves
 alves@systran.lu
Project Tradaut-Pt
Systran Luxembourg
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Re: Ada95 BNF

[Tucker Taft]

Martin Dowie wrote:
> 
> Ok... this seems a little strange to me - but if those are the rules! :-)
> 
> Is it really that hard to come up with a BNF that does actually match
> what the language does allow?

In many cases it is preferable to make the BNF somewhat
"looser" than the "official" grammar, and then do the
checking as part of semantic checking, because the errors
tend to be handled a bit more gracefully.  In addition,
in Ada, there are constructs which look identical
syntactically but which are distinct semantically, such
as a type conversion and an array indexing.  The grammar
in the LRM distinguishes these, whereas the grammar used
for an LR parser can't, since an LR parser requires that
the grammar be context-free (i.e. independent of the
"meaning" of particular identifiers).

-- 
-Tucker Taft   stt@avercom.net   http://www.averstar.com/~stt/
Chief Technology Officer, AverCom Corporation (A Titan Company) 
Burlington, MA  USA (AverCom was formerly the Commercial Division of AverStar:
http://www.averstar.com/services/ebusiness_applications.html)

Re: Ada95 BNF

[Martin Dowie]

Fair enough, but I still thnk it is strange that it
wasn't defined along the lines of:

defining_program_unit_name ::=
  [ parent_unit_name "." ] defining_identifier

parent_unit_name ::=
  identifier

given that "identifier" already exists and can be
navigated to through the existing definitions in
about 2 clicks and by-passing all the 'invalid'
options anyway...

:-)


Tucker Taft <stt@averstar.com> wrote in message
news:3AF80887.F8942BE3@averstar.com...
> Martin Dowie wrote:
> >
> > Ok... this seems a little strange to me - but if those are the rules!
:-)
> >
> > Is it really that hard to come up with a BNF that does actually match
> > what the language does allow?
>
> In many cases it is preferable to make the BNF somewhat
> "looser" than the "official" grammar, and then do the
> checking as part of semantic checking, because the errors
> tend to be handled a bit more gracefully.  In addition,
> in Ada, there are constructs which look identical
> syntactically but which are distinct semantically, such
> as a type conversion and an array indexing.  The grammar
> in the LRM distinguishes these, whereas the grammar used
> for an LR parser can't, since an LR parser requires that
> the grammar be context-free (i.e. independent of the
> "meaning" of particular identifiers).
>
> --
> -Tucker Taft   stt@avercom.net   http://www.averstar.com/~stt/
> Chief Technology Officer, AverCom Corporation (A Titan Company)
> Burlington, MA  USA (AverCom was formerly the Commercial Division of
AverStar:
> http://www.averstar.com/services/ebusiness_applications.html)

Re: Ada95 BNF

[Ted Dennison]

In article <3af8ded6$1@pull.gecm.com>, Martin Dowie says...
>
>Fair enough, but I still thnk it is strange that it
>wasn't defined along the lines of:
>
>defining_program_unit_name ::=
>  [ parent_unit_name "." ] defining_identifier
>
>parent_unit_name ::=
>  identifier
>
>given that "identifier" already exists and can be
>navigated to through the existing definitions in
>about 2 clicks and by-passing all the 'invalid'
>options anyway...
>
>:-)
>
>
>Tucker Taft <stt@averstar.com> wrote in message
>news:3AF80887.F8942BE3@averstar.com...
>> Martin Dowie wrote:
>> >
>> > Ok... this seems a little strange to me - but if those are the rules!
>:-)
>> >
>> > Is it really that hard to come up with a BNF that does actually match
>> > what the language does allow?
>>
>> In many cases it is preferable to make the BNF somewhat
>> "looser" than the "official" grammar, and then do the
>> checking as part of semantic checking, because the errors
>> tend to be handled a bit more gracefully.  In addition,
>> in Ada, there are constructs which look identical
>> syntactically but which are distinct semantically, such
>> as a type conversion and an array indexing.  The grammar
>> in the LRM distinguishes these, whereas the grammar used
>> for an LR parser can't, since an LR parser requires that
>> the grammar be context-free (i.e. independent of the
>> "meaning" of particular identifiers).
>>
>> --
>> -Tucker Taft   stt@avercom.net   http://www.averstar.com/~stt/
>> Chief Technology Officer, AverCom Corporation (A Titan Company)
>> Burlington, MA  USA (AverCom was formerly the Commercial Division of
>AverStar:
>> http://www.averstar.com/services/ebusiness_applications.html)
>
>

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