The problem is that `in-cycle' goes into a loop trying to generate an element. In the first case, `for' discovers that the first sequence runs out of elements before it even asks the second sequence for an element.
I don't see an alternative to this behavior, so I'll adjust the documentation to describe and warn about `in-cycle' on an empty sequence. I'll also change `in-sequences' and `in-cycle' to accept zero sequences, which would match the documentation, since there doesn't seem to be a reason to require a sequence. At Thu, 24 Nov 2011 20:57:10 -0700, Neil Toronto wrote: > In the following program, "loop 2 finished" is never printed, even > though `i' loops over nothing. As far as I understand, the second loop > shouldn't iterate at all - it should stop as soon as the `i' sequence is > finished, which is immediately. But I could be wrong, so I'm asking: is > this a bug? > > > #lang racket > > (for ([i (in-list empty)] > [j (in-cycle '(1))]) > (printf "i = ~v~n" i)) > > (printf "loop 1 finished~n") > > (for ([i (in-list empty)] > [j (in-cycle empty)]) > (printf "i = ~v~n" i)) > > (printf "loop 2 finished~n") > > > Neil T _________________________________________________ For list-related administrative tasks: http://lists.racket-lang.org/listinfo/users
