Re: [stack] language hierarchy

Don Groves <[email protected]> wrote:
> John Nowak wrote:
> > This has the downside that functions cannot make use of explicit
> > recursion (as hypot isn't defined until def is called, and hence the
> > quote can't make use of it), but this restriction is in place anyway
> > due to the type system.

> How about "self" as a call to its enclosing context?

It won't work for dynamic definitions, because there's no distinct
concept of "enclosing context". All you know is that you're inside a
quotation that's inside another quotation; you can't look ahead to see
which enclosure is the one being defined and/or executed. There are
several solutions:

1. Provide special syntax for quoted definitions (perhaps make them compiled).
2. Provide recursion primitives like linrec, genrec, etc.
3. Provide partial continuations.

#3 is especially interesting, since PCs can implement recursion or
backtracking equally easily. In a typefree language, it's very simple
to implement; in a typechecked language, of course, one additionally
has to ensure that the word which begins the partial continuation is
exposed to the same stack as the words which call it.

> Don

-Wm