Coming from the Haskell world, I sorely miss the speed of nailing a precise and elegant data model with sum types. Exhaustiveness checks are a big one for me.

Coming from the Haskell world, I sorely miss the speed of nailing a precise and elegant data model with sum types. Exhaustiveness checks are a big one for me. For each default case I wish that my type checker would be smarter. I know that records can have multiple constructors, but it escapes my why we cannot seal those records so exhaustiveness checks are free. A default case is somewhat like a final block for an exception, whereas I want compile time cursing. F# Sums are indeed nicer (also tons better syntax than Typescript uses).