7 ms·

Parser combinators in F# were where I really grasped the utility of a Monad. F# doesn’t have HKT’s, and computational expressions are a little different from Ha

• contravariant 5y ago
  In .NET I still find it weird that people sometimes implement the visitor pattern without the output type. You'd have to truly think imperatively to consider: void Structure(IVisitor visitor); a good function signature, instead of: A Structure(IParser<A> parser); I mean fair enough that you can't be bothered to implement the functor and monad methods, but it's downright silly to define a function that is incapable of returning output.
  • frabert 5y ago
    In .NET specifically a reason I can think about doing that is that you'd need to implement your visitor twice, as the type argument cannot be void (if I recall correctly).
    • Joker_vD 5y ago
      It can't be void, but writing public sealed class Unit { private static Unit m_value = new Unit(); public static Unit Value => m_value; public Unit() { } public override string ToString() => "()"; public override bool Equals(object obj) => obj is Unit; public override int GetHashCode(object obj) => 0; } and then using it ("return Unit.Value") in place of void is really not that big a problem.
    • contravariant 5y ago
      True, but I just never quite managed to understand why you'd want your visitor to return nothing. And if you did why it was too much hassle to just return '0' or something.