macro (action handle: (branches: Block))
  { handlers = branches contents map:
      { `(~c -> ~e) | `(~c -> !escape-handle yield: ~e)
      }

    `({ !escape-handle | ~action bind: ~(`Block new: handlers) } call/cc)
  } call

macro (a handle: (b: Block) ensuring: (c: Block))
  `({ ~a handle: ~b } ensuring: ~c)

(action: Block) catch: recover :=
  { cc |
    action bind: {
      Error -> { e | cc yield: (recover call: e) }
    }
  } call/cc

macro (a catch: (b: Block) ensuring: (c: Block))
  `({ ~a catch: ~b } ensuring: ~c)

(action: Block) ensuring: (cleanup: Block) :=
  action after: cleanup

v ensuring: p do: b :=
  { b call: v } ensuring: { p call: v }