[antlr-interest] Idea: semantic grammar

[Adam Connelly]

I totally agree.  What if you had a basic pre-defined collection that was
distributed, and then users could extend on it to add their own.  Then when
they were used in a parser, only the types that were actually used in the
grammar would be imported.

Like I say, I've not totally thought things through yet so any comments are
great.

Cheers,
Adam

2008/5/22 Johannes Luber <JALuber at gmx.de>:

> > Cheers for the replies.
> >
> > Johannes, I probably didn't phrase it quite right.  I wasn't suggesting
> > that
> > you define the actual semantics of the language (I thought about that but
> > temporarily moved it to the side).  What I was meaning is that for the
> > purposes of simpler (from the user's point of view) error reporting, it
> > should be possible to define the types of semantic errors that can occur
> > (but not necessarily how to detect these errors).
> >
> > Once these types were defined, when users create their semantic
> predicates
> > they could then "attach" a type to a predicate which would alter the type
> > of
> > exception thrown by the predicate, and in turn the error message that was
> > created.
> >
> > Something like (ignoring the actual syntax)
> >
> > {table.HasKey("myvar")}?[UndefinedIdentifier]
> >
> > It may also be good to be able to pass argument to the types, but I
> > haven't
> > thought that quite through.
> >
> > Does that make any more sense?
> > Adam
>
> It does. It's a nice idea, but things have to be extendable - not all
> semantic errors occur in a language.
>
> Johannes
>
> >
> > 2008/5/22 Johannes Luber <JALuber at gmx.de>:
> >
> > > > Hi,
> > > > I don't know if there is anything like this about at the moment, or
> > even
> > > > if
> > > > it's a good idea.  What I've been thinking about is having a grammar
> > that
> > > > defines the semantics of a language that parsers can then import.  It
> > > > would
> > > > basically be a list of the possible types of semantic error that
> could
> > > > occur, along with any information necessary to generate an error
> > message,
> > > > and an action that creates the message.
> > > >
> > > > >>From this a number of exception classes would be generated, along
> > with
> > > a
> > > > MessageCreator that would generate error messages based on the
> actions
> > > > supplied.  Inside the parser grammar, when semantic predicates are
> > > > declared,
> > > > the type of error would be indicated, and from this the correct
> > exception
> > > > would be thrown.  The parser would then ask its ErrorReporter to
> > handle
> > > > the
> > > > error, which would use the MessageCreator to create the error
> message,
> > > and
> > > > would then add it to a list / print to the console / whatever.
> > > >
> > > > >>From this, "catalogs" of pre-defined semantic errors could be
> > provided
> > > > along
> > > > with the correct messages to display for these errors.  Obviously
> this
> > > > wouldn't define the actual semantics of the language (since you'd
> > still
> > > > need
> > > > to implement this in actions), but it would simplify the error
> > reporting
> > > > part since users would just import the correct semantics, then
> > indicate
> > > > when
> > > > a certain semantic error should be thrown.
> > > >
> > > > Any thoughts?
> > > > Adam
> > >
> > > A nice idea but probably infeasible. There are too many semantic
> > > differences for basically one thing - recently I read an article about
> > "PHP
> > > sucks" and saw that references were handled in 4.3, 4.4 and 5
> > differently.
> > > Granted, 4.3 was leaky and 4.4 made it too complicated, so restricting
> > > options to sensible ones has a benefit, but if you want to be able to
> > parse
> > > even the most idiotic things, you have to able to define arbitrary
> > > semantics. And then you can use the target language itself.
> > >
> > > Maybe Yggdrasil of Loring Craymer can do that in target independent
> > manner,
> > > but it would be basically still Turing equivalent. At least you can do
> > far
> > > more things target independent in Yggdrasil than in ANTLR - just a
> > shame,
> > > that he didn't got around to finish it yet.
> > >
> > > Johannes
> > > --
> > > Der GMX SmartSurfer hilft bis zu 70% Ihrer Onlinekosten zu sparen!
> > > Ideal für Modem und ISDN: http://www.gmx.net/de/go/smartsurfer
> > >
>
> --
> Desperate Housewives - das Spiel!
> Pikante Skandale, schockierende Details unter: http://flat.games.gmx.de
>
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