shift and reset ¶I am working on the typed language implementation for Vicare; this code has its
own branch. To take a small break, I added to the boot image the code for the
syntaxes shift and reset which implement delimited continuations;
the code is in the current head of the master branch.
I am truly ignorant on delimited continuations, I just took the code from
http://mumble.net/~campbell/scheme/shift-reset.scm which implements the
syntaxes on top of call/cc and adapted it for embedding in Vicare. This
file claims:
This code is written by Taylor Campbell and placed in the Public Domain. All warranties are disclaimed.
I do not know the story of this implementation; I can see that it is similar to the one in the paper:
Martin Gasbichler, Michael Sperber: Final Shift for Call/cc: Direct Implementation of Shift and Reset, In The 2002 ACM SIGPLAN Conference on Functional Programming (ICFP ’02), Pittsburgh, Pa., October 2002, pages 271-282.
which is available on the Net. I have verified that the usual usage examples work:
(+ 1 (reset 2)) ⇒ 3 (reset (* 2 (shift K (K 3)))) ⇒ 6 (+ 1 (reset (* 2 (shift K (K 3))))) ⇒ 7 (reset (* 2 (shift K (K (K 2))))) ⇒ 8 (reset (* 2 (shift K (K (K (K 2)))))) ⇒ 16
In some future I should take the time to actually study the implementation and truly test it (I am especially concerned with the use of a internal parameter).