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Re: LIST-LENGTH & circular lists Sergei Egorov (19 Feb 1999 20:22 UTC)
The type-name prefix convention and LIST-... Olin Shivers (20 Feb 1999 00:25 UTC)

The type-name prefix convention and LIST-... Olin Shivers 20 Feb 1999 00:25 UTC

   From: "Sergei Egorov" <>
   Date: Fri, 19 Feb 1999 15:22:43 -0500

   Does this proposal imply that (LENGTH "abc") and (LENGTH '#(a b c)) return
   0? If it does, it will conflict with probably more 'natural' attempts to
   generalize LENGTH to accept other kinds of sequences. Calling it
   LIST-LENGTH does not affect existing programs and does not introduce any
   potential conflicts.

You can't fix this issue by simply changing the name LENGTH to LIST-LENGTH,
because it is pervasive throughout list-lib. You would have to change the
names of all these procedures:
   first second third fourth fifth sixth seventh eighth ninth tenth
   take drop take! drop! last (times 2, most likely, if we split these l/r)
   zip unzip2 unzip3 unzip4 unzip5
   append! reverse-append reverse-append!
   unfold unfold/tail foldl foldr reducel reducer
   append-map append-map! map! filter-map map-in-order
   filter  partition  remove
   filter! partition! remove!
   find any every
   del  delq  delv  delete
   del! delq! delv! delete!
   mem ass
   delq-duplicates  delv-duplicates  delete-duplicates  del-duplicates
   delq-duplicates! delv-duplicates! delete-duplicates! del-duplicates!
   append reverse
   member memq memv assoc assq assv
   map for-each

Any future generalisation of these functions to some sort of "sequence generic"
functions or OO messages will have to postulate an alternate module binding
these names to the generic functions/messages. I'd suggest that such a spec
would come in two parts: a spec for the new library, and a spec giving an
alternate set of bindings for the list-lib procs.

But this is really outside the bounds of this SRFI. I'm not willing to
pervasively tack "LIST-" onto the front of all these names; it would lard
up the names too much and would also break with current code practice in
what seems to me to be gratuitous fashion.

   Even with LIST-LENGTH, I still think that the proposed terminology shift
   is not justified in general LISP/Scheme context. The fact that
   (LIST-LENGTH 5) returns 0 makes you expect (LIST? 5) to return #t
   etc. What was wrong with IMPROPER-LIST?

Yes, this is a good point. If you have the notion that everything is a list,
then any procedure named LIST? that isn't (LAMBDA (X) #t) is probably going
to cause some confusion. This is exactly why my "Everything is a list"
msg proposed these three predicates, which *aren't* misleading in this
    circular-list? x -> boolean
    proper-list? x -> boolean
    dotted-list? x -> boolean

IMPROPER-LIST? is a perfectly fine thing. It's either of these:
    (conjunction circular-list? dotted-list?)
    (negate proper-list?)
Given that PROPER-LIST? exists, is it important to define IMPROPER-LIST?

Just to reiterate, I am now proposing to punt LIST? for exactly this reason,