adamc@841: datatype t = datatype Basis.option
adamc@841: 
adam@1544: val monad = mkMonad {Return = @@Some,
adam@1544:                      Bind = fn [a] [b] (m1 : t a) (m2 : a -> t b) =>
adam@1544:                                case m1 of
adam@1544:                                    None => None
adam@1544:                                  | Some v => m2 v}
adam@1544: 
adamc@846: fun eq [a] (_ : eq a) =
adamc@846:     mkEq (fn x y =>
adamc@846:              case (x, y) of
adamc@846:                  (None, None) => True
adamc@846:                | (Some x, Some y) => x = y
adamc@846:                | _ => False)
adamc@846: 
adamc@961: fun ord [a] (_ : ord a) =
adamc@961:     mkOrd {Lt = fn x y =>
adamc@961:                    case (x, y) of
adamc@961:                        (None, Some _) => True
adamc@961:                      | (Some x, Some y) => x < y
adamc@961:                      | _ => False,
adamc@961:            Le = fn x y =>
adamc@961:                    case (x, y) of
adamc@961:                        (None, _) => True
adamc@961:                      | (Some x, Some y) => x <= y
adamc@961:                      | _ => False}
adamc@961: 
adamc@944: fun isNone [a] x =
adamc@944:     case x of
adamc@944:         None => True
adamc@944:       | Some _ => False
adamc@944: 
adamc@841: fun isSome [a] x =
adamc@841:     case x of
adamc@841:         None => False
adamc@841:       | Some _ => True
adamc@844: 
adamc@844: fun mp [a] [b] f x =
adamc@844:     case x of
adamc@844:         None => None
adamc@844:       | Some y => Some (f y)
adamc@846: 
adamc@846: fun bind [a] [b] f x =
adamc@846:     case x of
adamc@846:         None => None
adamc@846:       | Some y => f y
adamc@1068: 
adamc@1068: fun get [a] (x : a) (o : option a) =
adamc@1068:     case o of
adamc@1068:         None => x
adamc@1068:       | Some v => v
mad@1831: 
mad@1831: fun unsafeGet [a] (o : option a) =
mad@1831:     case o of
mad@1831:         None   => error <xml>Option.unsafeGet: encountered None</xml>
mad@1831:       | Some v => v