I disagree, and since we are talking about the expression problem, we should not be conflating dynamic dispatching code which could be statically resolved from dynamic dispatching code which is necessarily dynamic.<p>A standard use-case of dynamic dispatch is for representing different types of term in a parse tree, where we want to dispatch on nodes according to type. This sort of dispatch cannot be monomorphised, since the the exact callee depends on the shape of the trees being traversed and this almost certainly cannot be figured out statically.<p>In Haskell, you do not do this sort of dispatch with typeclasses, but instead use ADTs.<p>When it comes to the expression problem, the tradeoff is that ADTs allow you to easily write new sorts of traversal but do not allow you to extend the tree type in a modular way. By contrast, single dispatch OO allows you to easily extend the tree type by providing new classes to implement the traversal methods, at the cost that you cannot easily define new traversals.