MAPing Sequences

[MURRAY%cs.umass.edu@RELAY.CS.NET]

>  It has not been established that it is a bug for sequence functions not
>  to handle circular lists.  There seems to be strong sentiment on both
>  sides of this issue, and there is no clear statement on this in the
>  manual.  At some point the standardization committee will have to make a
>  decision one way or the other.

Calling it a Bug was my own opinion.  I should more careful, and I aplogize
for any confusion.

>  If it were up to me (which it isn't) it would be an error to pass a
>  circular list to any function that does not explicitly allow circular
>  lists.  I don't think the extra cost of handling this style is justified
>  for most functions.  Sequences should be finite.

>  -- Scott

Extra cost for what?  Using lists as sequences? 
LENGTH and ELT are not constant-time operations on lists.  AT LEAST FOR
THE MAPPING FUNCTIONS, it is a poor implementation which forces 
every cons of a list to be looked at (paged in)
if they will never be used by the function since some other sequence
is shorter. It is equally poor to scan the first N-1 elements of
a list every time to get the Nth.  Whether sequences can be
infinite or not, an inefficient implementation technique that doesn't
support them seems like a poor reason to not allow them.

Kelly Murray