Lexing space seperated words in ANTLR3 where some words are keywords

I am working on a project that involves transforming part of speech tagged text into an ANTLR3 AST with phrases as nodes of the AST.

The input to ANTLR looks like:

DT-THE The NN dog VBD sat IN-ON on DT-THE the NN mat STOP .

i.e. (tag token)+ where neither the tag or the token contain white space.

Is the following a good way of lexing this:

WS :  (' ')+ {skip();};
TOKEN : (~' ')+;

The grammar then has entries like the following to describe the lowest 开发者_如何学编程level of the AST:

dtTHE:'DT-THE' TOKEN -> ^('DT-THE' TOKEN);
nn:'NN' TOKEN -> ^('NN' TOKEN);

(and 186 more of these!)

This approach seems to work but results in a ~9000 line Java Lexer and takes a large amount of memory to build (~2gb) hence I was wondering whether this is the optimal way of solving this problem.

Could you combine the TAG space TOKEN into a single AST tree? Then you could pass both the TAG and TOKEN into your source code for handling. If the Java code used to handle the resulting tree is very similar between the various TAGs, then you could perhaps simplify the ANTLR with the trade-off of a bit more complication in your Java code.