status: withdrawn (2023-06-29)
Continuation marks are a programming language feature that allows one to attach information to and retrieve information from continuations, generalizing stack inspection. Conceptually, a continuation consists of a number of frames where each frame stands for an active procedure call that is not a tail call. A continuation mark is then a key-value pair associated with a frame, with keys compared using
eq?. At most one mark for a given key can be attached to a single frame.
Besides stack inspection, continuation marks can be used to implement dynamic scope, delimited continuations, or delayed evaluation that is able to handle iterative lazy algorithms.
This SRFI proposes to add continuation marks to the Scheme programming language. The interface defined here is modelled after Racket's continuation marks. It does not include all forms and procedures provided by Racket but provides a compatible subset.