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|
datatype t = datatype Basis.option
val monad = mkMonad {Return = @@Some,
Bind = fn [a] [b] (m1 : t a) (m2 : a -> t b) =>
case m1 of
None => None
| Some v => m2 v}
fun eq [a] (_ : eq a) =
mkEq (fn x y =>
case (x, y) of
(None, None) => True
| (Some x, Some y) => x = y
| _ => False)
fun ord [a] (_ : ord a) =
mkOrd {Lt = fn x y =>
case (x, y) of
(None, Some _) => True
| (Some x, Some y) => x < y
| _ => False,
Le = fn x y =>
case (x, y) of
(None, _) => True
| (Some x, Some y) => x <= y
| _ => False}
fun isNone [a] x =
case x of
None => True
| Some _ => False
fun isSome [a] x =
case x of
None => False
| Some _ => True
fun mp [a] [b] f x =
case x of
None => None
| Some y => Some (f y)
fun app [m] [a] (_ : monad m) (f : a -> m {}) x =
case x of
None => return ()
| Some y => f y
fun bind [a] [b] f x =
case x of
None => None
| Some y => f y
fun get [a] (x : a) (o : option a) =
case o of
None => x
| Some v => v
fun unsafeGet [a] (o : option a) =
case o of
None => error <xml>Option.unsafeGet: encountered None</xml>
| Some v => v
fun mapM [m] (_ : monad m) [a] [b] (f : a -> m b) (x : t a) : m (t b) =
case x of
None => return None
| Some y => z <- f y; return (Some z)
|
