Re: tail call reduction

[Oliver Scholz <alkibiades@gmx.de>]

Stefan Monnier <monnier@iro.umontreal.ca> writes:

>> My main pet Emacs Lisp programming project involves both a lot of
>> parsing and recursively descending of tree-like data structures.
>
> Can you give a short description of one such case where you've bumped
> into problems.  After all, the lack of tail-recursion should only be
> a problem when you implement loops by recursive calls, but unless your tree
> data-structures are very deep, normal recursion should fine.

I don't recall the actual cases where I bumped into problems. IIRC I
got beyond `max-lisp-eval-depth' once or twice with recursive
functions on a depth-first traversal of medium-sized trees. Since the
default of said variable is 300, this should be o.k.. Hm, well, I
guess it was with a loop implemented by recursive calls.

>> But, alas, unless I am much mistaken, proper tail recursion is simply
>> impossible in a dynamically scoped environment.  I could reduce byte
>
> I recommend you check out the lexbind branch which introduces static scoping
> (it still provides dynamic scoping as well, but it should allow tail-call
> elimination in most simple cases).

Ah, of course! Thanks a lot! Wow, it seems, this Emacs manages lexical
variables on the stack ... I am impressed.

    Oliver
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