module type Basic2 =Multi parameter monad. The second parameter get unified across all the computation. This is used to encode monads working on a multi parameter data structure like (sig
..end
('a,'b result)
).
The signature is exactly the same as for S1
except S.unit
which got
pruned. (We cannot write let unit = return ()
without forcing the
'd
parameter of ('a, 'd) monad
to be covariant.)
type ('a, 'b)
t
val bind : ('a, 'b) t ->
('a -> ('c, 'b) t) -> ('c, 'b) t
val return : 'a -> ('a, 'b) t