catchException "fail"
  <try>
  | catchException "fail"
  |   <try>
  |   | pushInput
  |   | read (\u1 -> Term)
  |   | popValue
  |   | popException "fail"
  |   | loadInput
  |   | raiseException "fail"
  |   <handler>
  |     loadInput
  |     pushValue Term
  |     popException "fail"
  |     ret
  <handler>
    pushInput
    lift2Value Term
    choicesBranch [(\u1 -> u1)]
      <branch>
      | raiseException "fail"
      <default>
        raiseException "fail"