arrows

[Magnus Carlsson]

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