[antlr-interest] org.antlr.runtime.tree.RewriteEmptyStreamException
David Maier
David.Maier at ingres.com
Wed Jul 7 09:42:20 PDT 2010
Hi again,
thanks for your quick reply Andrew. But shouldn't the following rule be enough to make ANTRL aware of that it can be void:
sp_decls: (sp_decl ';')* -> (sp_decl)*;
I mean that the Kleene operator (*) means to also match the empty word, right? So I think the following is true for rules named 'a', 'b' and 'c':
(1) My variant
a : b;
b : c*;
with
c* := /*empty*/ | c+
and if I resolve it then 'a' means:
a: /*empty*/ | c+
(2) Your variant
a: b?;
b: c*;
with
b?:= /*empty*/ | b
b:= /*empty*/ | c+
and so
a:= /*empty*/ | /*empty*/ | c+ := /*empty*/ | c+
So you can see that both should mean the same. So is it a kind of ANTLR issue that I would have to use the (?) operator here?
Regards, David
--
David Maier
Senior Software Engineer
Ingres Germany GmbH
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D-98693 Ilmenau
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MAIL: david.maier at ingres.com
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-----Ursprüngliche Nachricht-----
Von: antlr-interest-bounces at antlr.org im Auftrag von Andrew Haley
Gesendet: Mi 07.07.2010 18:22
An: antlr-interest at antlr.org
Betreff: Re: [antlr-interest]org.antlr.runtime.tree.RewriteEmptyStreamException
On 07/07/2010 05:19 PM, David Maier wrote:
> Hello,
>
>
> I am getting the following error message as Output of a tree generating grammar which I am currently writing.
>
> Exception in thread "main" org.antlr.runtime.tree.RewriteEmptyStreamException: rule sp_decls
> at org.antlr.runtime.tree.RewriteRuleElementStream._next(RewriteRuleElementStream.java:158)
> at org.antlr.runtime.tree.RewriteRuleElementStream.nextTree(RewriteRuleElementStream.java:145)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.sp_block_content(MySQLASTGenParser.java:10730)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.sp_unlabeled_block(MySQLASTGenParser.java:9691)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.sp_proc_stmt(MySQLASTGenParser.java:8577)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.sp_tail(MySQLASTGenParser.java:1691)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.no_definer_tail(MySQLASTGenParser.java:1541)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.view_or_trigger_or_sp_or_event(MySQLASTGenParser.java:1401)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.create(MySQLASTGenParser.java:1260)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.stmt(MySQLASTGenParser.java:1186)
> at com.ingres.antlr.idiom.mysql.MySQLASTGenParser.prog(MySQLASTGenParser.java:1117)
> at __Test__.main(__Test__.java:16)
>
> So the last rules are looking as the following:
>
> sp_unlabeled_block:
>
> sp_block_content
>
> ;
>
> sp_block_content:
> BEGIN_SYM
>
> sp_decls
> sp_proc_stmts
> END -> sp_decls sp_proc_stmts //To ignore the BEGIN and END
> ;
>
> sp_decls: (sp_decl ';')* -> (sp_decl)*;
>
> sp_decl:
> DECLARE_SYM sp_decl_idents
>
> type
> (sp_opt_default)? -> ^(TN_DECLARE ^(TN_PARAMS sp_decl_idents type) ^(TN_TODO sp_opt_default)?)
>
>
> | DECLARE_SYM ident CURSOR_SYM FOR_SYM sp_cursor_stmt -> ^(TN_DECLARE ^(TN_NAME ident) ^(TN_SELECT sp_cursor_stmt))
>
> ;
>
>
> There is a TN_CODE token type which I want to use as the root node of the subtree which will then have this TN_DECLARE nodes as child nodes. So I only did rewrite the rules 'between' TN_CODE and TN_DECLARE to remove unnecessary information like the ';' or the BEGIN and END keywords.
>
> So I guess that the error occurs because my test input does not have a DECLARE section, but this is OK because of the rule 'sp_decls: (sp_decl ';')* -> (sp_decl)*;
> ' which says that there could be even no one (*=0 or multiple). So has anybody an answer what is causing the issue and how to solve it?
sp_decls might be void. Try
sp_block_content:
BEGIN_SYM
sp_decls
sp_proc_stmts
END -> sp_decls? sp_proc_stmts //To ignore the BEGIN and END
;
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