What is continuation-passing style?

If a language supports continuations, the programmer can add control constructs like exceptions, backtracking, threads and generators.

Sadly, many explanations of continuations feel vague and unsatisfying. Such power deserves a solid pedagogical foundation.

Continuation-passing style is that foundation.

Continuation-passing style gives continuations meaning in terms of code.

Even better, a programmer can discover continuation-passing style by themselves if subjected to one constraint:

No procedure is allowed to return to its caller — ever.

One hint makes programming in this style possible:

Procedures can take a callback to invoke upon their return value.

When a procedure is ready to “return” to its caller, it invokes the “current continuation” callback (provided by its caller) on the return value.

A continuation is a first-class return point.

• Implementing :

Continuation passing style can be used to implement continuations and control flow operators in a functional language that does not feature first-class continuations but does have first-class functions and tail-call optimization.