On Mon, Mar 22, 2010 at 09:16:34PM +0100, Andy Wingo wrote: > Hi Josef, > > I seem to be the negative guy in replies to you.
Uh? I did not notice anything negative? > Apologies for that! I don't see any reason for you to apologize... > On Mon 22 Mar 2010 20:25, Josef Wolf <j...@raven.inka.de> writes: > > > On Fri, Mar 19, 2010 at 08:54:02AM -0400, Ken Raeburn wrote: > >> > >> The result of (if #f #f) is unspecified, not #f, according to r5rs. > >> That means an implementation can produce whatever value it wants. > > In the R6RS, evaluating `(if #f #f)' returns "unspecified values" -- > that is, even the number of values is unspecified. And in fact it would > make sense for `(if #f #f)' to be the same as `(values)' -- an > expression returning zero values. As I understood this, the "no values" variant is a guile extension and not guaranteed by the standard... > > I think I like this type of "unspecified". Much better than the > > "undefined behavior" definition in C. > > Unfortunately it really is unspecified :) OK it's better than C, in the > sense that it won't launch the missiles, but it would be better if > evaluating: > > (+ 2 (if #f #f)) > > yielded an error of "too few values to continuation" rather than "don't > know how to add #<unspecified>". Even better would be "too few values for '+'" or something. Oh, and a line number.
