[Haskell-cafe] Monadifying pickler combinators

[Joel Reymont]

Folks,

I'm trying to monadify http://research.microsoft.com/~akenn/fun/ 
picklercombinators.pdf

appU is easy but I can't figure out the appP. Is it actually  
possible? The clever trick seems to be the passing of (b -> a) into  
sequ for use in appP.

--
instance Monad (PU s) where
     return a = PU snd (\s -> (a, s))
     -- how do I do appP below?
     pa >>= k = PU (\(b, s) -> let pb = k a
                               in appP pa (a, ???

     -- this is good
                   (\s -> let (a, s1) = appU pa s
                              pb = k a
                          in appU pb s1)

	Thanks, Joel

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