astgen conditions

[GoogleCodeExporter]

With immutable data structures it is sometimes convenient to be able to
"change" one field:
  Command newCommand = oldCommand.changeLabels(emptyList);
To be able to generate code for changeLables one would need to write a
template like
  \members{
    public \ClassName change\MemberName(\MemberType newMember) {
      return new \ClassName(\members[,]
        {\if{\MemberName==\MemberName[1]}{newMember}{\memberName}});
    }
  }
or something similar.

There are two things that must be done to get the template above to work:
1. support references to outer loops, as in \MemberName[0], \MemberName[1]
2. evaluate conditions

Original issue reported on code.google.com by radugrig...@gmail.com on 19 Aug 2009 at 5:54