A OO-style encoding of sum types in Nix

maybe.nix

let 

    build = match: rec {
        inherit match;
        map = f: match nothing (a: just(f a));
        bind = f: match nothing (a: f a);
        isJust = f: match false (a: true);
        isNothing = f: match true (a: false);
        show = match "Nothing" (a: "Just ${toString a}");
        toList = match [] (a: [a]);
    };

    just = a: build (ifNothing: ifJust: ifJust a);

    nothing = build (ifNothing: ifJust: ifNothing);

in { 

    inherit just nothing; 

    usage = {
    
        mappingNothing = 
            (nothing.map (a: a + 1)).toList;

        mappingJust = 
            ((just 1).map (a: a + 1)).toList;

        bindingNothing =
            (nothing.bind (a: if a > 0 then just (a + 1) else nothing)).toList;

        bindingJust =
            ((just (1)).bind (a: if a > 0 then just (a + 1) else nothing)).toList;

        bindingJust' = 
            ((just (-1)).bind (a: if a > 0 then just (a + 1) else nothing)).toList;

    };

}