[antlr-interest] What does " The following alternatives can never be matched" mean

[Gavin Lambert]

At 20:30 2/12/2009, David-Sarah Hopwood wrote:
 >You probably want these to be lexer rules, i.e.
 >
 >  prog     : command+ ;
 >  command  : (Function | Var)+ ;
 >
 >  Function : ('A'..'Z')+ ',' ;
 >  Var      : ('A'..'Z')+ ;
 >  WS       : ( '\t'|' '|'\r'|'\n'|'\u000C' )+ { $channel = 
HIDDEN;
 >} ;

Actually it's probably better to keep function/var out of the 
lexer:

prog : command+ ;
command : (function | var)+ ;
function : ID COMMA ;
var : ID ;

fragment Letter : 'A'..'Z';
COMMA : ',' ;
ID : Letter+ ;
WS : ( '\t'|' '|'\r'|'\n'|'\u000C' )+ { $channel = HIDDEN; }