Before teaching any data structure course, one MUST learn functional languages with ADTs. It makes everything so easy to understand. So, it MUST be a first language in every institution. The biggest reason that one should learn functional languages with algebraic data type(ADT)s first is because understanding recursive definitions. If you recursion first, understanding iteration and mutable data structures are dead simple and easy: they are just alternate representation or optimization. However, when you learn while loops and for loops first, your brain gets damaged and a lot of students gets stuck when they first see the Tower of Hanoi, the notorious in-place quicksort routine written in imperative languages, you'll get to think of recursion as some stack blowing up monster that must be unrolled and managed manually. Furthermore, learning data structures in most traditional imperative language literature gives you the impression that linked list and binary trees are brain-fucking spaghetti monsters of memory pointers all the cells, which is a dead simple recursive definition in functional languages with ADTs. Personally, I never really understood what linked list was before I learned ML and Haskell, although I've used doubly linked list in a C++ standard library, which was to me a black box that meets the specification in some huge standard document, for two years.