[antlr-interest] "Coarse grained" errors in antlr

[David Ferrao]

Hi and apologies for the newbie question.

I am trying to build an autocomplete mechanism using antlr error messages,
but am facing a problem where the parser seems to bail out one rule earlier
than I  would like.
To illustrate, consider the following grammar snippet.

--------Antlr 3 snippet-------
create  : 'CREATE'  stream;
stream    : 'STREAM' qname 'TYPE' stream_types;
stream_types : map_schema| java_bean|xml_schema;
map_schema    :'MAP_SCHEMA' '{' (value_list)? '}';
java_bean    :'JAVA_BEAN' '(' class_name ')' '{' '}';
xml_schema    :'XML_SCHEMA' '(' string_literal ')' '{' '}';

....contd...

---------end Grammar------

Given the string "CREATE STREAM system:TEST TYPE MAP_SCHEMA" as input, the
parser generates the following NoViableAltException

"36:1: stream_types : ( map_schema | java_bean | xml_schema );"

This is a completely logical error considering that the parser cannot match
either "map_schema" or  "java_bean" or "xml_schema".
However, it is not very helpful for my auto complete scenario which would be
better served by an error message stating that a '{' was expected.
I was wondering if there is any option /technique to coax the parser to
start executing and consequently throw a NoViableAltException in the
"map_schema" rule, considering that the input DOES contain the 'MAP_SCHEMA'
token.

Would deeply appreciate any inputs, I have skimmed through the 'Definitive
ANTLR reference', but still couldnt come up with a solution :(

Thanks
David
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