> I wish i could apply f x y instead of lift $ f <$> x <*> pure y. In "Applicative Programming with Effects"[0], the authors use such a notation, and even leav

> I wish i could apply f x y instead of lift $ f <$> x <*> pure y. In "Applicative Programming with Effects"[0], the authors use such a notation, and even leave it as an exercise to implement it in Haskell using MultiParamTypeClasses: > Given Haskell extended with multi-parameter type classes, enthusiasts for overloading may replace ‘⟦’ and ‘⟧’ by identifiers i[ and ]i with the right behaviour. So they have code that looks like eval :: Exp v -> Env v -> Int eval (Var x) = fetch x eval (Val i) = ⟦ i ⟧ eval (Add p q) = ⟦ (+) (eval p) (eval q) ⟧ > Yes so why doesn’t some GHC extension do this? It's possible to derive the functor instance automatically if the data type is built from products, sums and arrows. However even for Applicatives you can't do this in general because there can be many lawful Applicative instances for the same type, for instance[1] for lists. [0] http://strictlypositive.org/IdiomLite.pdf http://strictlypositive.org/IdiomLite.pdf [1] https://hackage.haskell.org/package/base-4.16.1.0/docs/Control-Applicative.html#t:ZipList https://hackage.haskell.org/package/base-4.16.1.0/docs/Contr...