giogonzo

// Porting of the "Arithmetic expressions" example at https://en.wikibooks.org/wiki/Haskell/GADT

// (partially) related TS discussions:
// - https://github.com/microsoft/TypeScript/issues/12424
// - https://github.com/microsoft/TypeScript/issues/17325

// Definition of `Expr` in Haskell using GADTs
// data Expr a where
//     I   :: Int  -> Expr Int
//     B   :: Bool -> Expr Bool