[antlr-interest] what means "mismatched input 'xxx' expecting set null"
antlr at mirality.co.nz
Sat Oct 6 22:57:13 PDT 2007
At 17:51 7/10/2007, Pete Siemsen wrote:
>: INCLUDE LPAREN f=StringConstant RPAREN
>The above grammar produces the error. What's wrong?
Since PragmaInclude is a lexer rule, it won't discard whitespace
(or to be more specific, it won't generate whitespace tokens and
then either skip them or push them onto a hidden channel). So
anywhere that whitespace may occur within a lexer rule you will
need to explicitly specify it.
>Perhaps it's relevant that if I change the "P" on "PragmaLocale"
>to "p", I get this error instead:
>line 1:8 no viable alternative at input 'include'
>line 2:8 no viable alternative at input 'include'
>line 3:8 no viable alternative at input 'include'
It's hard to say for this one -- you've specified "StringConstant"
in your rule but haven't actually given a definition for it in the
grammar you posted. If that's actually what you've got (or if
StringConstant is a fragment rule), then that's your
problem. Parser rules can only (usefully) refer to non-fragment
lexer rules that the lexer will actually generate :) (ANTLR won't
complain about typos, irritatingly -- it assumes you are referring
to another token it simply hasn't seen the definition for yet --
even if it never does.)
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