OK, I have made some progress, and have uploaded two programs to lpaste.net * one that works: trifecta + unbound, works: http://lpaste.net/108457 * and one that doesn't trifecta + unbound, fails http://lpaste.net/108458 the working version is simpler, in that it defines PiParser just as a type synonym type PiParser = FreshMT InnerParser maybe I should be happy already that I got that working, e.g.
parseTest (runInnerParser $ runFreshMT $ whiteSpace *> many identifier) " wow {- bla -} this rocks" ["wow","this","rocks"]
to install: cabal install trifecta + unbound in a sandbox e.g. Now in the second version, I have in addition wrapped the FreshMT in a newtype newtype FreshT m a = F { runF :: FreshMT m a } deriving (Monad, Functor, Applicative, MonadPlus, MonadTrans) type PiParser = FreshT InnerParser While this might not be necessary in this simple case here, I can imagine situations, where doing so might come in handy. Consequently have to add a few more instances for the parser: instance CharParsing PiParser where etc. and of course I need an additional step of unwrapping with runF runInnerParser $ runFreshMT $ runF someparser (In both versions TokenParser is defined on the PiParser) I would expect that I can parse something like the above test string similarily, but unfortunately this is not the case:
parseTest (runInnerParser $ runFreshMT $ runF (whiteSpace *> many identifier)) " oh too {- bla -} bad" []
I can at most parse one letter:
parseTest (runInnerParser $ runFreshMT $ runF (whiteSpace *> identifier)) "oh too {- bla -} bad" "o"
I don't really see, how wrapping the FreshMT in a newtype harms the parser? Thanks in advance -Andreas