{ lists are represented using pairs as in homework 3,
  using the following encoding:

  cons h t -> pair h t
  nil -> 0
  head l -> fst l
  tail l -> snd l
  isnil l -> (not (ispair l))
  
}

(letfun map f (letfun m xs (if (ispair xs)
                         	(pair (@ f (fst xs)) (@ m (snd xs)))
				xs)
		       m)
   (letfun plus1 x (+ x 1)
      (let g (@map plus1)
           (@g (pair 1 (pair 2 (pair 3 0)))))))  { should yield (2.(3.(4.0))) }