gistfile1.hs

module std;

export Maybe;
export Nothing;
export Just;

export force;
export isNothing;

Maybe<a> = variant Nothing, Just(a)

force<a> :: Maybe<a> -> a;

force(Just(x)) := x;
force(Nothing) := error "forced a Nothing";

isNothing :: Maybe<a> -> Bool;

isNothing(Just(_)) := false;
isNothing(Nothing) := true;