In F#, when you implement an interface, it's an equivalent of explicit interface implementation in C#. That is, you can call the method through the interface, but not directly through the class.
F# reference article about interfaces suggests adding a method that does the upcasting to the type:
type Dog (name : string) =
member this.Name = (this :> Animal).Name
interface Animal with
member this.Name : string = name
Or, as suggested by Daniel, you can do it the other way around, which means you can avoid that cast:
type Dog (name : string) =
member this.Name = name
interface Animal with
member this.Name : string = this.Name
Also, the .Net convention for interface names is to start them with I
, so your interface should be called IAnimal
.