[r6rs-discuss] [Formal] Requirement to detect circular lists

From: William D Clinger <will>
Date: Wed Oct 4 08:52:16 2006

I am posting this as an individual member of the Scheme
community. I am not speaking for the R6RS editors, and
this message should not be confused with the editors'
eventual formal response.

Andre van Tonder wrote:
> > Andre van Tonder wrote:
> >
> >> I think the arguments must be checked up front for all the higher order
> >> procedures.
> >
> > Yes.
>
> I see... In that case I reverse my prior retraction of the formal comment :-\
)
>
> Performance will now clearly be adversely affected.

You misquoted me by deleting the part of your statement
with which I agreed, leaving only a part of your statement
with which I disagree.

The arguments can be checked at any time before the
first return from the procedure. For example, a
concurrent thread can check the arguments while
another thread performs the R5RS-compatible work.

Many other variations are possible. Please note
also that I have not commented on the performance
of checking for plausible lists in the higher order
procedures. My only remarks concerning performance
had to do with the performance of checking in the
length procedure, which is the procedure you were
talking about at the time.

Will
Received on Wed Oct 04 2006 - 08:52:13 UTC