[Haskell-cafe] Musings on type systems

[Tillmann Rendel]

Ketil Malde wrote:
>   data Sum a b = A a | B b -- values = values in a + values in b
>   data Prod a b = P a b    -- values = values in a * values in b
>
> I guess this makes [X] an exponential type, although I don't remember
> seeing that term :-)

I would expect the "exponential type" to be (a -> b):

 > type Exp b a = a -> b -- values = values in b ^ values in a

   Tillmann