Tutorial or Article

[Tathams]

Can anyone suggest something for me to read to learn and understand look ahead
and fall back.

I am have trouble writing a partial C pre-processor and wish to create a few
non-terminals to handle the many different #xxxx things that can occur in
header files.

So if I have a non-terminal to handle #if or #ifdef then another to handle
#elif and a final to handle #else like so

/* ISO/IEC 9899:201x (6.10) */
if_group 
 : NUMBER_SIGN KEYWORD_IF constant_expression NEW_LINE group
 | NUMBER_SIGN KEYWORD_IF constant_expression NEW_LINE
 | NUMBER_SIGN KEYWORD_IFDEF IDENTIFIER NEW_LINE group
 | NUMBER_SIGN KEYWORD_IFDEF IDENTIFIER NEW_LINE
 | NUMBER_SIGN KEYWORD_IFNDEF IDENTIFIER NEW_LINE group
 | NUMBER_SIGN KEYWORD_IFNDEF IDENTIFIER NEW_LINE
 ; 

/* ISO/IEC 9899:201x (6.10) */
elif_groups 
 : elif_group
 | elif_groups elif_group
 ;

/* ISO/IEC 9899:201x (6.10) */
elif_group 
 : NUMBER_SIGN KEYWORD_ELIF constant_expression NEW_LINE group
 | NUMBER_SIGN KEYWORD_ELIF constant_expression NEW_LINE
 ;

/* ISO/IEC 9899:201x (6.10) */
else_group 
 : NUMBER_SIGN KEYWORD_ELSE NEW_LINE group
 | NUMBER_SIGN KEYWORD_ELSE NEW_LINE
 ;

How do I not fail when the�NUMBER_SIGN finds an ELSE rather than a IF.

Regards
Stephen



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