Re: Ada95 BNF

[Tucker Taft <stt@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)