[R6RS] Will `map' order remain unspecified?

William D Clinger will at ccs.neu.edu
Sun Jun 25 14:52:47 EDT 2006

Mike wrote:
> Subject says all: The order in which `map' processes the elements of
> the list is specified.  Will it remain that way?  (Maybe we decided
> this and I missed it.  I'd be grateful if someone could remind me in
> that case.)

While I am generally opposed to excessive over-specification,
expecting map to process its elements from left to right has
been perhaps the most common order-of-evaluation bug in R5RS
programs.  In order to catch this bug more often, and to
increase the portability of R6RS-conforming programs, I
therefore propose that map be required to process the
elements of its list arguments in the order used by Chez
Scheme [1].


[1]  That order appears to be: from left to right for elements
with odd index, followed by right to left for elements with
even index.  Kent, please correct me if I got this wrong.

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