Hello, I am a bit confused about command stacks. I tried to run the following code in ghc: mshowA :: (Arrow a, Show b) => a (b, String) String mshowA = proc (x,s) -> returnA -< s ++ show x ++ s f :: Arrow a => a Int String f = proc x -> do a <- (mshowA -< x) "***" returnA -< a To my understanding (this doesn't mean anything :-) this is correct because (mshowA -< x) "***" should be equivalent to (mshowA -< (x,"***")), but somehow ghc is rejecting the code with the error message "Non-empty command stack at command: mshowA -< x". The arrow pre-processor from Ross Paterson compiles the code with no problems to ordinary haskell and the resulting code runs as expected in ghc, so, my question is, what's wrong? Me, ghc, arrowp... Thanks in advance for every answer or hint you can give me ...Sebastian