Re: [Haskell-cafe] Question on declaring an instance

On Mon, May 19, 2008 at 2:02 AM, john lask wrote:

Consider the data type:

Foo i o a = ...

we want to declare an instance of Monad and Arrow for Foo without using a newtype (repackaging). The effect we want is to be able to construct an expression like:

( f>> g )>>> ( h>> i )

where f, g, h, i :: Foo i o a, for some i o a

[...]

Can Foo be declared an instance of both Arrow and Monad ?

I think not. However, it's not unreasonable for data Foo i o To be both monad and arrow, since arrows are functors in their second argument. Luke