Are there any static duck-typed languages?

Question

Can I specify interfaces when I declare a member?

After thinking about this question for a while, it occurred to me that a static-duck-typed language might actually

Answer 1

F# supports static duck typing, though with a catch: you have to use member constraints. Details are available in this blog entry.

Example from the cited blog:

let inline speak (a: ^a) =
    let x = (^a : (member speak: unit -> string) (a))
    printfn "It said: %s" x
    let y = (^a : (member talk: unit -> string) (a))
    printfn "Then it said %s" y

type duck() =
    member x.speak() = "quack"
    member x.talk() = "quackity quack"
type dog() =
    member x.speak() = "woof"
    member x.talk() = "arrrr"

let x = new duck()
let y = new dog()
speak x
speak y