[Haskell-cafe] more thoughts on "Finally tagless"

[Martijn van Steenbergen]

Tom Schrijvers wrote:
> data EvalDict sem = EvalDict { val :: Int -> sem Int, add :: sem Int
> -> sem Int -> sem Int }

An alternative option is to capture the structure in a GADT:

> data Eval a where
>   Val :: Int -> Eval Int
>   Add :: Eval Int -> Eval Int -> Eval Int

And then write what were instances before as functions Eval a -> whatever.

Of course, this makes it harder to combine multiple models.

Martijn.