> Additionally lambda syntax, aka python anonymous first class functions HAVE to be functional.

They have to be a single python expression, but that’s not the same as the usual understanding of “functional” (i.e., referentially transparent). Consider:

  d = {"foo": 1}
  f = lambda m: d.update({k, v+d.get(k,0) for k,v in m.items()}) or d

> Tail slices on lists like x[1:] cost O(N) and that's the biggest issue right now imo. It makes some valid solutions on leetcode exceed the time limit because it adds and additional N complexity on every slice when the head and tail functions in haskell cost O(1)

Python lists are not lisp-style lists, which is more efficient for most uses, but not for a lot of functional-style algorithms which leverage cheap head/tail splits.

But it wouldn't be hard to write a typed sequence class that wrapped a lisp-style immutable list implemented with nested tuples with the deepest nested one an empty tuple in Python, there's just not a lot of demand for it.