[mruts]

I wouldn't call Lisp a functional language. Historically it's not functional, and in practice it usually isn't functional either.

When I hear "functional", I usually interpret it to mean languages influenced or derived from the ML family of languages. Notable features of these languages include algebraic data types, match expressions, emphasis on monadic operations (fold, scan, map, etc), support for TCO, and a expressive static type system (though unfortunately not necessarily supported higher kinds), and a discouragement of mutations.

Common Lisp doesn't really emphasize any of those things, and Scheme only a couple.

[pjmlp]

That is describing Miranda and Haskell.

F#, Standard ML, Caml Light and Objective Caml would fail that bullet point list.

[mruts]

What points do ML languages fail on? They have everything I listed.

[pjmlp]

TCO (you need explicitly rec annotations), immutability (ref cells, array types), existence of imperative control structures.

[mruts]

Just because you need a red annotation doesn’t mean they don’t have TCO. Most people consider Scala to have TCO, and you need rec annotations as well. Also I said mutation is discouraged for ML languages, not that it hard. Point taken about the imperative control structures, though.

[pjmlp]

Right, the generated machine code also matters.

Scala has partial TCO, surely not cross recursive calls like Scheme language standard requires and how it is defined from CS point of view.

Same applies to F#, because neither JVM nor CLR have direct support for TCO.