Constant.applicative
new applicative identity combine creates the dictionary for a constant applicative functor.
new applicative identity combine
method map' : ('c r, 'e, 'a, 'b, 'D) map'm
method pure' : ('c r, 'e, 'a, 'D) pure'm
method pair' : ('c r, 'e, 'a, 'b, 'D) pair'm