continuation

noun

Sometime it is tricky to ensure that code gets done at the right time, and end up in the right place.The answer is to pass in a fuction that will tell us what code to generate later. Such a function is often called a continuation, because it tells us where to continue computing.

Shriram Krishnamurthi

Quoting his textbook "Programming Languages: Application and Interpretation"

Capturing Continuations

In Scheme, we create a value representing the continuation using one of two related constructs. The traditional form is called call/cc, short for “call with current continuation”. call/cc consumes a procedure as an argument, and invokes this procedure with a continuation. That is, uses of call/cc typically look like

(call/cc

(lambda (k)

··· k ···)) ;; k is the continuation

Because the extra lambda is extremely tiresome, however, Scheme provides a nicer interface to capturing the current continuation: you may instead equivalently write

(let/cc k

··· k ···)) ;; k is bound to the continuation

Note that let/cc is a binding construct: it introduces a new scope, binding the named identifier (k, above) in that context. For the rest of this material, we’ll use let/cc rather than call/cc.