FunFact.fs

(* Fun fact: It is possible to define the Cons (::) symbolic union case
used by FSharp's own list data structures for your own discriminated unions. *)

type MyList<'t> = 
| Nil
| (::) of 't * MyList<'t>

let x = 100::99::98::Nil 
//The compiler will infer this to be of type MyList<int> since I explicitly used the Nil union case of MyList
//And not the [] union case of List.

//You can do this as well, but it doesn't really work as expected.

type MyList2<'t> = 
| ([])
| (::) of 't * MyList<'t>

let x = 5::4::3::[]
//The compiler will always infer the basic List type over my own discriminated union.