I am trying to parse this portion of an email header:
Received: from server.mymailhost.com (mail.mymailhost.com [126.43.75.123]) by pilot01.cl.msu.edu (8.10.2/8.10.2) with ESMTP id NAA23597;Fri, 12 Jul 2002 16:11:20 -0400 (EDT)
I want the lexer to tokenize it into these pieces:
Received:
from server.mymailhost.com (mail.mymailhost.com [126.43.75.123])
by pilot01.cl.msu.edu (8.10.2/8.10.2)
with ESMTP
id NAA23597
;
Fri, 12 Jul 2002 16:11:20 -0400 (EDT)
<EOF>
Here's my parser grammar:
parser grammar MyParser;
options { tokenVocab=MyLexer; }
received : Received fromToken byToken withToken idToken SemiColon date EOF ;
fromToken : FromText ;
byToken: ByText ;
withToken : WithText ;
idToken : IdText ;
date : DateContents+ ;
Below is my lexer grammar. This is the error that I get when I run ANTLR:
token recognition error at: 'from server.mymailhost.com (mail.mymailhost.com [126.43.75.123]) by pilot01.cl.msu.edu (8.10.2/8.10.2) with ESMTP id NAA23597;Fri, 12 Jul 2002 16:11:20 -0400 (EDT)'
mismatched input '<EOF>' expecting FromText
Apparently the lexer is successfully getting the first token (Received:
) but then is not getting the next token (From:
). Note that in the lexer grammar I am using lookahead; am I using it correctly? Any thoughts on what the problem is?
lexer grammar MyLexer;
Received : 'Received: ' ;
SemiColon : ';' ;
FromText : 'from ' .+?
{
(self.input.LA(1) == 'b') and (self.input.LA(2) == 'y')
}? ;
ByText : 'by '.+?
{
(self.input.LA(1) == 'w') and (self.input.LA(2) == 'i') and (self.input.LA(3) == 't') and (self.input.LA(4) == 'h')
}? ;
WithText : 'with ' .+?
{
(self.input.LA(1) == 'i') and (self.input.LA(2) == 'd')
}? ;
IdText : 'id ' .+?
{
(self.input.LA(1) == ';')
}? ;
DateContents : ('Mon' | 'Tue' | 'Wed' | 'Thu' | 'Fri' | 'Sat' | 'Sun') (Letter | Number | Special)+ ;
fragment Letter : 'A'..'Z' | 'a'..'z' ;
fragment Number : '0'..'9' ;
fragment Special : ' ' | '_' | '-' | '.' | ',' | '~' | ':' | '+' | '$' | '=' | '(' | ')' | '[' | ']' | '/' ;
Whitespace : [\t\r\n]+ -> skip ;
After much effort I figured out the answer. Here is the working lexer:
lexer grammar MyLexer;
Received : 'Received: ' ;
SemiColon : ';' ;
FromText : 'from ' .+?
{(self._input.LA(1) == ord('b')) and (self._input.LA(2) == ord('y'))}?
;
ByText : 'by '.+?
{(self._input.LA(1) == ord('w')) and (self._input.LA(2) == ord('i')) and (self._input.LA(3) == ord('t')) and (self._input.LA(4) == ord('h'))}?
;
WithText : 'with ' .+?
{(self._input.LA(1) == ord('i')) and (self._input.LA(2) == ord('d'))}?
;
IdText : 'id ' .+?
{(self._input.LA(1) == ord(';'))}?
;
DateContents : ('Mon' | 'Tue' | 'Wed' | 'Thu' | 'Fri' | 'Sat' | 'Sun') (Letter | Number | Special)+ ;
fragment Letter : 'A'..'Z' | 'a'..'z' ;
fragment Number : '0'..'9' ;
fragment Special : ' ' | '_' | '-' | '.' | ',' | '~' | ':' | '+' | '$' | '=' | '(' | ')' | '[' | ']' | '/' ;
Whitespace : [\t\r\n]+ -> skip ;