two LET rewrites

;;https://stackoverflow.com/questions/60331920/
;;partial-application-versus-pattern-matching-why-do-these-haskell-functions-beha

memfib = -- (!!) (map fib [0..])
  let
    fib 0 = 0
    fib 1 = 1
    fib k = memfib(k-2) + memfib(k-1)
    --?1-- map_fib = (map fib [0..])
  in
     --?2-- (!!) (map fib [0..])
     --?1-- (!!)  map_fib                 -- what GHC does

memfib_param -- n = ((!!) (map fib [0..])) n
             = \n ->
  let
    fib 0 = 0
    fib 1 = 1
    fib k = memfib_param (k-2) + memfib_param (k-1)
  in
    ((!!) (map fib [0..])) n