[antlr-interest] Keeping lookahead low

[Ciaran Treanor]

Following on from the help provided by Alexey and Olivier yesterday
I've cleaned up a test grammar I was working on and am left with one
question outstanding.

I have a test data file that looks like the following:
System {
 foo = Th       ! case 1:  BROKEN - rhs should be considered an ID
 foo = Thing    ! case 2: BROKEN - rhs should be considered an ID
 foo = Thing123 ! case 3: GOOD - rhs is a THING_ID
 foo = Thingy   ! case 4: GOOD - rhs is a regular id
 foo = foo      ! case 5: GOOD - rhs is a regular id
 Th = foo       ! case 6: BROKEN - lhs should be considered an ID
 Thing = foo    ! case 7: BROKEN - lhs should be considered an ID
 Thing123 = foo ! case 8: Why is error "expecting '}'" instead of expecting ID
 Thingy = foo   ! case 9: GOOD - lhs is a regular id
}

Can anyone tell me why the parser fails with the following error when
it endounters 'Th' or 'Thing'?
Exception in thread "main" line 2:11: expecting 'i', found ' '
       at com.ct.test.TestLexer.nextToken(TestLexer.java:120)
       at antlr.TokenStreamHiddenTokenFilter.consume(TokenStreamHiddenTokenFilter.java:38)
       at antlr.TokenStreamHiddenTokenFilter.nextToken(TokenStreamHiddenTokenFilter.java:134)
       at antlr.TokenBuffer.fill(TokenBuffer.java:69)
       at antlr.TokenBuffer.LA(TokenBuffer.java:80)
       at antlr.LLkParser.LA(LLkParser.java:52)
       at antlr.Parser.match(Parser.java:210)
       at com.ct.test.TestParser.systemBlock(TestParser.java:82)
       at com.ct.test.TestParser.testFile(TestParser.java:61)
       at com.ct.test.TestParser.main(TestParser.java:31)

Increasing lookahead to 6 fixes case 1 and case 2. Unfortunately
increasing the lookahead isn't really an option for me since, in
reality, 'Thingy' is actually a 20 character word.

What's the simplest thing I can do to the grammar to fix the cases
above that I've flagged as broken?

Oh, can anyone explain the error reported for case 8. This case is an
assignment that looks like:
THING_ID = ID

Since the grammar is expecting assignments of the form ID = ( ID |
THING_ID) I would have thought the parser would complain that it found
a THING_ID when it was expecting a regular ID. Instead it compains
about expecting '}'. Why is that?

Thanks a million (oh, grammar and test file attached)
ct
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