Option evaluation operator for F#

OptionExtension.fs

type OptionDefault<'a> =
| Default of 'a
| Lazy of (unit->'a)
| Expected of reason:string

let (|.) (opt:'a option) (def:OptionDefault<'a>) : 'a =
  match opt with
  | Some (v) -> v
  | None ->
    match def with
    | Default(v) -> v
    | Lazy(factory) -> factory ()
    | Expected(reason) -> failwith reason