How to control order of imported lexer grammar rules and local lexer rules?

[Thomas Beale]

I have a top level grammar, call it mylang.g4; it imports some common patterns including patterns to match whitespace (call it base_patterns.g4), identifiers, all the usual primitive types, and it also has its own lexer rules to recognise keywords.

The problem is that the imported base_patterns.g4 rules for things like IDENTIFIER are matching keywords in an input text being processed by mylang.g4, at least that is what I think is happening.

The file structure is:

~~~~~~ base_patterns.g4 ~~~~~~~~~~

lexer grammar ;

IDENTIFIER : .... ; // etc

~~~~~~~~~~~~~~~~~~~~~~~~~~~~~~

~~~~~~ mylang.g4 ~~~~~~~~~~

grammar ;

import base_patterns;

// lexer patterns

SYM_DESCRIPTION : [Dd][Ee][Ss][Cc][Rr][Ii][Pp][Tt][Ii][Oo][Nn] ; // 'description' keyword

SYM_CARDINALITY : [Cc][Aa][Rr][Dd][Ii][Nn][Aa][Ll][Ii][Tt][Yy] ; // 'cardinality' keyword

// etc

~~~~~~~~~~~~~~~~~~~~~~~~~

but when an input text is parsed, 'cardinality' is matched as an IDENTIFIER. 

To avoid this, I could presumably create mylang_keywords.g4 and then do 

import mylang_keywords, base_patterns ;

but this seems an annoying proliferation of files. Any other solution?

- thomas

[Jim Idle]

Essentially, your keywords need to be seen before your IDENTIFIER rule. So, you can probably just change the point where you import your patterns to be after you have specified the grammar specific rules. 

Jim

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