[Haskell-cafe] Question on declaring an instance
lrpalmer at gmail.com
Sun May 18 22:11:14 EDT 2008
On Mon, May 19, 2008 at 2:02 AM, john lask <jvlask at hotmail.com> 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.
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