Question

I have a source that has embed information in comment. For example

//IP x = 3
//IP y = 20

Normally, “//” is marked for comment, but “//IP” is used for indicating set setup information.

How can I parse the comment to get value for x and y?

I may be able to have these lexer rules, but I’m not sure about the action part. Can I extract BASIC_IDENTIFIER values?

BASIC_IDENTIFIER
   :    ('a'..'z' | 'A'..'Z') ( '_' |  ('a'..'z' | 'A'..'Z') |  ('0'..'9') )*
   ;

IP_COMMENT
  : '//IP' (BASIC_IDENTIFIER\s?'='\s?BASIC_IDENTIFIER) ( ~'\n' )* {???}
  ;  

COMMENT
  : '//' ( ~'\n' )* {$channel=HIDDEN;}
  ;

Answer 1

Header and Member

// START:members
@header {
using System.Collections.Generic;
}

@members {
public static Dictionary<string, string> memory = new Dictionary<string, string>();
}

Grammar Rule Change

DECIMAL_LITERAL
   :    ('0'..'9') ( '_' |  ('0'..'9') )* ( ( '.' ('0'..'9') ( '_' |  ('0'..'9') )* )? ( EXPONENT )? )
   ;

BASIC_IDENTIFIER
   :    ('a'..'z' | 'A'..'Z') ( '_' |  ('a'..'z' | 'A'..'Z') |  ('0'..'9') )*
   ;

IP_COMMENT
  : '--IP' (' ')+ (id = BASIC_IDENTIFIER) (' ')* '=' (' ')* (val = DECIMAL_LITERAL| var = BASIC_IDENTIFIER) ( ~'\n' )* {VHDLParser.memory[$id.text] = $val.text; $channel=HIDDEN;}
  ;  

COMMENT
  : '--' ( ~'\n' )* {$channel=HIDDEN;}
  ;

Now the parsed value is in Dictionary, so you can get the key/value pair.

foreach (KeyValuePair<string, string> kvp in VHDLParser.memory)
{
    Console.WriteLine("{0} - {1}", kvp.Key, kvp.Value);
}