ML was implemented in Stanford Lisp on a DEC10. The layout of the language is very lispy. Make parens around functions non-optional and add them around let, and a couple other constructs makes the code almost indistinguishable from lisp. First-class functions everywhere, linked lists, and garbage collection were also very-much tied to lisp at the time. Initially being implemented on top of Lisp is probably a key reason these were present.