This package by MichaelAbrahamShulman allows the definition of coroutines in Emacs Lisp.

From the commentary: A coroutine is a function that can return (“yield”) a value and still retain its execution state so that at the next call it can pick up where it left off.

Coroutines are very difficult to implement without the aid of first-class continuations or a similar control feature, and this imposes certain limits: for example, ‘yield’ is only valid at top-level in the coroutine, or inside a specially tweaked macro.

these links are broken, and I can’t find them anywhere else, so am uploading them here: Lisp:coroutine.el Lisp:tagbody.el

The following should make edebug grok tagbody/go

    (def-edebug-spec tagbody (&rest [&or symbolp integerp form]))
    (def-edebug-spec go      (&or symbolp integerp))
    (def-edebug-spec go*     (form))

CategoryCode CategoryExtensions