Jeesh,

I have an MA in mathematics but without knowing category theory, it has been opaque to me till just now that the monoids discussed around Haskel are the same beast I briefly dealt with in abstract algebra. Indeed, only by looking up monoid and appendable did this become semi-evident.

The Haskellians don't even help you out enough to point towards ordinary abstract but instead send you all the way to category theory with sign-posts along the way.

The abstract structure monoid may not really be fully described by appendable but it's a leg-up. The objects in object-orientation get extended by convenience but the term object still helps the learner feel like they've got something concrete.