Meh, you'd use fold, map or filter 99% of the time in a functional language like scala or haskell. TCO is great, but you can still write a lot of idiomatic functional stuff even without it.
Right! TCO is not essential to practical functional programming. TCO is essential to practical use of the subset of functional programming that insists on recursion instead of iteration, including fold/map/filter.
TCO is an under-the-hood behaviour that the programmer would count on for practical performance. There's no reason that under-the-hood magic can't be in the implementation of fold/map/filter as primitive control ops.
It's just an accident of history that the [mp]atriarch functional programming language is Lisp, a language that was created in the name of proving a point about recursion. Recursion as the solution-to-all-problems is not essential to functional thinking. The essential ideas are first-class functions, higher-order functions, and referential transparency.
I think this mistake is comparable to thinking that classes are essential to object-orientation. I think many people are confused by university professors who love Scheme (for reasonable reasons), and who like to pretend that Lisps are the only alternatives to Fortran (arguably true in the '60s).
