[R6RS] Will `map' order remain unspecified?

dyb at cs.indiana.edu dyb at cs.indiana.edu
Mon Jul 10 08:46:15 EDT 2006

> 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].

This order was not always used in Chez Scheme and I don't believe that it
is ever used in the latest version.

I am opposed to specifying the processing order, but if we do, I think
right-to-left would be a sufficient to prevent people from counting on the

This is something that perhaps ought to go in an implementors guide.  The
user-level description should say the order is unspecified, but
implementors should be encouraged to choose something other than
left-to-right order.


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