Comment by nh2

10 hours ago

In Haskell they are a little less annoying. It is just easier to reason about (including proving) pure functions.

2 comments

nh2

I meant the constrained types by hiding the constructors. Super annoying, not automatically convertible, in Haskell you have to remember what the fake constructor is called, and write it every time you use it, but at least it's efficiently implemented with newtype, unlike the Java OOP version. Think about writing a value with several nested constrained types, like NonEmptyListOne (makeNonZeroNumber 42, 'h' `NonEmptyString` "ello world"). It's just really annoying.

_jackdk_ 8 hours ago

The blog link I mentioned avoids this cost with literals, by providing using a required type argument to check the string length at compile time without TH. It requires a relatively recent GHC:

    make :: forall symbol -> (IsNonEmptySymbol symbol) => NonEmptyText

    type family IsNonEmptySymbol symbol :: Constraint where
      IsNonEmptySymbol "" = Unsatisfiable (Text "Expected a non-empty string")
      IsNonEmptySymbol _ = (()::Constraint) -- empty constraint is always satisfied