Re: [Haskell-cafe] type class question

Ben schrieb:

dear haskellers --

i'm trying this question again, in haskell-cafe. i got some responses in haskell-beginners but am looking for more guidance. also, i understand this functionality is encapsulated in the Workflow module in hackage, but i'd like to understand this myself. this email is an (il)literate haskell file.

suppose i have class of computations a -> State s b. for concreteness, let's say i'm writing a library of on-line statistical summary functions, like

I used functions of such type to describe causal processes. In order make them an arrow, I had to hide the state s using existential quantification. http://code.haskell.org/synthesizer/core/src-4/Synthesizer/Causal/Process.hs