[antlr-interest] import construct - parsing each module once

[Jeroen van Schagen]

The language I'm currently implementing contains import constructs. So far
I've used the standard import implementation from the ANTLR wiki which goes:

import: 'import' moduleId -> 'import' moduleId ^( {
parseFile($moduleId.path) } ) ;

However this implementation will hang on circular dependancies and reduce my
parser performance when having multiple imports to the same module. So I
decided to keep a list of all the modules I've parsed so far, meaning I only
have to parse each module once. This has resulted in the following
implementation:

imprt: 'import' moduleId {
if(! modules.contains($moduleId.path)) {
Object dependancy = adaptor.becomeRoot(parseFile($moduleId.path), (Object)
adaptor.nil());
adaptor.addChild(root_0, dependancy);
}
}

@member { CommonTree parseFile(String path) { ... } }

The implementation works, however I would like a cleaner solution,
preferably using a rewrite rule. Any suggestions?

Thanks in advance!
Jeroen
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