[antlr-interest] Syntactic predicates cause unexplainable compilation errors in different partsof the code

[Peter Robinson]

On Wed, 2005-01-26 at 22:48, Loring Craymer wrote:
> This is one of those cases that is usually handled by factoring out the comma:
> 
> gene_ref:
>        gene_refline ("," gene_refline)*
>        ;
> 

Thanks, I did consider that but was stumped because of the following.
When I parse a GeneRef object, I create a Java object to store the info
that in turn gets passed further up. I need to initialize up to 6
different variables in this object depending on which type of
gene_refline are found (mainly strings, but also more complicated
structures). This is why I wanted to try to do everything in one rule so
that I would always have the reference to the GeneRef object handy...

gene_ref returns [GeneRef gr=null]
{
	String s;
} GENEREF_KW { gr = new GeneRef(); }
	s=gene_refline { gr.addString(s); }  // But there are 6
					//different types of String 					//variable to be initialied
			//depending on what type of gene_refline



> However, I think what you are really running into is ANTLR 2's approximate 
> LLk.  If you look at the generated code (without the synpreds), I think 
> that you will find that it does the right thing.
> 

It was actually (nearly) correct, but since a bunch of downstream
analyses depend on correct parsing, I would somehow like to get rid of
all error messages...


Monty, thanks for your reply. Yes I did look at the ASN.1 grammar on the
website, but (given that I am not that well versed in ASN.1, at least
not yet) I was not able to adapt that to my needs...




> --Loring
> 
> 
> At 12:34 PM 1/26/2005, Peter Robinson wrote:
> 
> 
> >Gene-ref ::= SEQUENCE {
> >      A VisibleString OPTIONAL ,
> >      B VisibleString OPTIONAL ,
> >     C VisibleString OPTIONAL ,
> >     D VisibleString OPTIONAL ,
> >     E BOOLEAN DEFAULT FALSE ,
> >     F SET OF Dbtag OPTIONAL ,
> >     G SET OF VisibleString OPTIONAL ,
> >     H  VisibleString OPTIONAL }
> >   END
> >
> >
> >
> >
> >Dear ANTLR list,
> >
> >First of all thanks to you all for being a helpful and informative list.
> >I recently have been trying to learn antlr and cannot now imagine using
> >things like lex/yacc with which I previously occasionally did things.
> >
> >I am now trying to parse a file structure from NCBI in ASN.1 format. The
> >specification of a small part of the entire thing is as follows  ( I
> >have replaced some keywords with the letters A-H for clarity). Any one
> >of the entries is optional and is followed by a comma if there is going
> >to be another line. There are Gene-ref entries with only one entry (and
> >no comma).
> >
> >
> >Gene-ref ::= SEQUENCE {
> >      A VisibleString OPTIONAL ,
> >      B VisibleString OPTIONAL ,
> >     C VisibleString OPTIONAL ,
> >     D VisibleString OPTIONAL ,
> >     E BOOLEAN DEFAULT FALSE ,
> >     F SET OF Dbtag OPTIONAL ,
> >     G SET OF VisibleString OPTIONAL ,
> >     H  VisibleString OPTIONAL }
> >   END
> >
> >After trying constructs such as (",")? and getting nondeterminateness
> >warnings, I tried my hand at a syntactic predicate as follows:
> >
> >generef_line returns [myJavaObject ... ]
> >{
> >         String s;
> >         Dbtag d;
> >}: GENE_KW "{"
> >        (        ( A STRING ",")=>
> >            A  s1:STRING { System.out.println(s1.getText()); }  ","
> >         |  A  s2:STRING { System.out.println(s2.getText()); }
> >         )?
> >         (  (B STRING ",")=>
> >            B s3:STRING { System.out.println(s3.getText()); } ","
> >         |  B s4:STRING {  System.out.println(s4.getText()); }
> >         )?
> >         AND SO ON...
> >
> >         "}"
> >;
> >
> >
> >However, this now causes unexplainable compilation errors in other parts
> >of the code (about 400 lines of grammar etc) to appear, in code that
> >**worked perfectly fine** before. What is going on?? and is there a
> >better way to parse the above construct? Thanks, Peter
> >
> >--
> >Peter N. Robinson
> >peter.robinson at t-online.de
> >peter.robinson at charite.de
> >http://www.charite.de/ch/medgen/robinson/
-- 
Peter N. Robinson
peter.robinson at t-online.de
peter.robinson at charite.de
http://www.charite.de/ch/medgen/robinson/