val return : 'result -> ('a, 'b, 'result) tval (>>>) :
('i1, 'model, 'r1) t ->
('r1, 'model, 'r2) t ->
('i1, 'model, 'r2) tval (>>|) : ('input, 'model, 'r1) t -> ('r1 -> 'r2) -> ('input, 'model, 'r2) tval (@>>) :
('i1 -> 'i2) ->
('i2, 'model, 'result) t ->
('i1, 'model, 'result) t