[Haskell-cafe] type class question

Henning Thielemann schlepptop at henning-thielemann.de
Wed Sep 30 19:28:11 EDT 2009

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


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