Question

I want to implement Maybe from Haskell in D, just for the hell of it.
This is what I’ve got so far, but it’s not that great. Any ideas how to improve it?

class Maybe(a = int){ }  //problem 1: works only with ints

class Just(alias a) : Maybe!(typeof(a)){ }

class Nothing : Maybe!(){ }


Maybe!int doSomething(in int k){

  if(k < 10)
    return new Just!3;  //problem 2: can't say 'Just!k'
  else
    return new Nothing;
}

Haskell Maybe definition:

data  Maybe a = Nothing | Just a

Answer 1

Look at std.typecons.Nullable. It’s not exactly the same as Maybe in Haskell, but it’s a type which optionally holds a value of whatever type it’s instantiated with. So, effectively, it’s like Haskell’s Maybe, though syntactically, it’s a bit different. The source is here if you want to look at it.