Editing Continuation (section)

==Kinds==
Support for continuations varies widely. A programming language supports ''re-invocable'' continuations if a continuation may be invoked repeatedly (even after it has already returned).  Re-invocable continuations were introduced by [[Peter J. Landin]] using his '''J''' (for Jump) operator that could transfer the flow of control back into the middle of a procedure invocation.  Re-invocable continuations have also been called "re-entrant" in the [[Racket (programming language)|Racket]] language.  However this use of the term "re-entrant" can be easily confused with its use in discussions of [[Thread (computing)|multithreading]].

A more limited kind is the ''escape continuation'' that may be used to escape the current context to a surrounding one. Many languages which do not explicitly support continuations support [[exception handling]], which is equivalent to escape continuations and can be used for the same purposes. C's <code>[[setjmp/longjmp]]</code> are also equivalent: they can only be used to [[stack unwinding|unwind the stack]].  Escape continuations can also be used to implement [[tail call elimination]].

One generalization of continuations are [[delimited continuation]]s. Continuation operators like <code>call/cc</code> capture the ''entire'' remaining computation at a given point in the program and provide no way of delimiting this capture. Delimited continuation operators address this by providing two separate control mechanisms: a ''prompt'' that delimits a continuation operation and a ''reification'' operator such as <code>shift</code> or <code>control</code>. Continuations captured using delimited operators thus only represent a slice of the program context.