Re: a rehash of the question of optimizing some prompt ideoms

[Mark H Weaver]

Hi Stefan,

Stefan Israelsson Tampe <address@hidden> writes:
> Delimeted continuations can be looked upon as a generalization of
> common lisps tagbody e.g. it's trivial to produce tagbody semantics
> with the help of prompts.

I haven't yet digested the rest of your email, but I wanted to point out
that prompts are not needed to produce Common Lisp 'tagbody' semantics.
All that's needed is a set of mutually-recursive local procedures that
tail call each other.  Each local procedure corresponds to a label, and
the tail calls correspond to GOTOs.

In fact, one of the earliest papers on Scheme, "LAMBDA, The Ultimate
Imperative" published in 1976, showed how to convert arbitrary Lisp
'PROG' forms into a very early version of Scheme.  Note that Lisp 'PROG'
was a combined 'let', 'block', and 'tagbody', and can do everything that
Common Lisp's 'tagbody' can do.

    Regards,
      Mark