(let discard
  (fn a T Nil ())
)

(let if
  (fn (cond iftrue iffalse) (Bool T T) T
    (case cond
      (true iftrue)
      (_ iffalse))
  )
)


(let ++
  (fn x Int Int
    (+ x 1)
  )
)


(let --
  (fn x Int Int
    (- x 1)
  )
)


(let sum (fix
  (fn sum' ((Vector (Int ...)) -> Int)
           ((Vector (Int ...)) -> Int)
    (fn vec (Vector (Int ...)) Int
      (case vec
        ((h ..t) (+ h (sum' t)))
        (_ 0))
    )
  )
))


(let map-i->i (fix
  (fn map'       (((Vector (Int ...)) (Int -> Int)) -> (Vector (Int ...)))
                 (((Vector (Int ...)) (Int -> Int)) -> (Vector (Int ...)))
    (fn (vec fun) ((Vector (Int ...)) (Int -> Int)) (Vector (Int ...))
      (case vec
      ((h ..t) (<> (vector (fun h)) (map' t fun)))
      (_ (() Int)))
    )
  )
))


(let filter-int (fix
  (fn filter'     (((Vector (Int ...)) (Int -> Bool)) -> (Vector (Int ...)))
                  (((Vector (Int ...)) (Int -> Bool)) -> (Vector (Int ...)))
    (fn (vec pred) ((Vector (Int ...)) (Int -> Bool)) (Vector (Int ...))
      (case vec
        ((h ..t) (
	    if (pred h)
	      (<> (vector h) (filter' t pred))
	      (filter' t pred))
	)
        (_ (() Int))
      )
    )
  )
))