Language Extensions - Haskell and Cryptocurrencies

Language Extensions

DataKinds

Promotion (aka DataKinds) allows us to automatically lift (non-GADT) datatypes to the kind level.

We define:

data Nat = Zero | Suc Nat

We can use Nat as a type and Nat as a kind.

We can use Zero and Suc as terms, and 'Zero and 'Succ as types.

The leading quote to indicate promotion is only required to resolve ambiguities and can otherwise be omitted.

code:datakind.hs

data Nat = Zero | Suc Nat

-- Normal interpretation:

Nat :: *

Zero :: Nat

Suc :: Nat -> Nat

-- Promoted interpretation:

'Zero :: Nat

'Suc ::Nat->Nat

DeriveFunctor, Foldable, Traversable

Allowing for automatic derivation of #Functor , Foldable, and #Traversable

Generalized Algebraic Datatypes (GADTs)

KindSignatures

RankNTypes

Rank-2 polymorphism is quantifies a function argument.

RecordWildType

Allow the use of wildcards in record construction and pattern matching.

code:rwt.hs

data Person = Person {

name :: String

, age :: Int

}

introduce :: Person -> String

introduce Person@{..} = "Hi, I'm " ++ show name ++

". my age is " ++ show age

StandaloneDeriving

TypeApplications

Explicitly apply a type in Haskell, using the @ operator.

code:typeapplications.hs

strange :: String -> String

strange = show . read @ Int

XOverloadedStrings

Useful links