### Continuing

[
  Datatype continuing
  Funcon   continued
  Funcon   finalise-continuing
  Funcon   continue
  Funcon   handle-continue
]


Meta-variables
  T <: values


Datatype
  continuing ::= continued
/*
  `continued` is a reason for abrupt termination.
*/


Funcon
  finalise-continuing(X:=>T) : =>T|null-type
   ~> finalise-abrupting(X)
/*
  `finalise-continuing(X)` handles abrupt termination of `X` due to executing
  `continue`.
*/


Funcon
  continue : =>empty-type
   ~> abrupt(continued)
/*
  `continue` abruptly terminates all enclosing computations until it is handled.
*/


Funcon
  handle-continue(_:=>null-type) : =>null-type
/*
  `handle-continue(X)` terminates normally when `X` terminates abruptly for the
  reason `continued`.
*/
Rule
                   X --abrupted( )-> X'
  ------------------------------------------------------
  handle-continue(X) --abrupted( )-> handle-continue(X')
Rule
                   X --abrupted(continued)-> _
  --------------------------------------------
  handle-continue(X) --abrupted( )-> null-value
Rule
                   X --abrupted(V:~continuing)-> X'
  ------------------------------------------------------
  handle-continue(X) --abrupted(V)-> handle-continue(X')
Rule
  handle-continue(null-value) ~> null-value