[antlr-interest] AST with optional parameters

[Bart Kiers]

Jim,

>From an earlier message, David wrote: *"Yes, the language is Matlab and a
semicolon on the end of an assignment expression suppresses display of the
result of the assignment. ..."*

Bart.


On Tue, Jun 7, 2011 at 6:30 PM, Jim Idle <jimi at temporal-wave.com> wrote:

> Why do you want the SEMI in your AST?
>
> Jim
>
> > -----Original Message-----
> > From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> > bounces at antlr.org] On Behalf Of David Smith
> > Sent: Tuesday, June 07, 2011 4:41 AM
> > To: antlr-interest at antlr.org
> > Subject: [antlr-interest] AST with optional parameters
> >
> > I'm parsing a grammar in which the semicolon on the end of a line is
> > optional. So two of the statement rules might be:
> >     |   (ID GETS expr SEMI) => ID GETS expr SEMI -> ^(GETS ID expr
> > SEMI)
> >     |   (ID GETS) => ID GETS expr -> ^(GETS ID expr)
> > Since this occurs with a number of different assignment statements, I
> > would really like to collapse this into one rule that looks something
> > like this:
> >     |   (ID GETS) => ID GETS e=expr (s=SEMI)? -> ^(GETS ID $e $s)
> > but every implementation I can think of either refuses to generate the
> > grammar or, as in the case above, generates the grammar but decides
> > that the variable 's' is unknown.
> > Is there a any way to achieve this?
> >
> >                                  DMS
> >
> > David M. Smith http://www.cc.gatech.edu/fac/David.Smith
> > Georgia Institute of Technology, College of Computing Sent from my ASR-
> > 33 Teletype
> >
> >
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