Re: arrows

Koen Claessen writes:

* Stream processors (from Fudgets) are nice arrows:

data SP a b = Get (a -> SP a b) | Put a (SP a b) | Nil

But the first operator assumes that the product type associated with this arrow must be Haskell's product (,), but in fact a sum type would make a much nicer product.

I made an attempt to parameterize the arrow type over the type that should be used to form environments. Indeed, I used the sum type for the stream processor instance of arrows. I modified Ross Paterson's preprocessor to take advantage of this generalization. Some slides about this and an implementation can be found at http://www.cse.ogi.edu/~magnus/ProdArrows/ All the best, /M