Lambda the Ultimate

This is (I believe) a simple, trivial question. Is there any difference between Haskell style "where" clauses on function definitions and using similar "letrec", "letfn" or "labels" forms in other languages. We can restrict the definitions within these forms to plain function definitions, for the sake of argument.

So where we might have (forgive any syntactic faux pas).

list-len Nil = 0
list-len _:xs = list-len' 1 xs
  where 
    list-len' acc Nil = acc
    list-len' acc _:xs = list-len' (acc + 1) xs

Can we always substitute an equivalent (using a hypothetical labels form, for the sake of argument):

list-len xs =
   labels
      list-len' acc Nil = acc
      list-len' acc _:ys = list-len' (acc + 1) ys
   in
      case xs of
        Nil = 0
        _::zs = list-len' 1 zs

I'm just curious if these "where" clauses are naught more than syntactic surgar for other forms more familiar to me. Thanks much in advance, and no, this is *not* a homework assignment (I'm 45 years old today).

- Scott.