If you create a program using the example provided for sequence!() you get a compilation error: /usr/local/include/d/phobos2/std/functional.d(191): Error: static assert "Bad binary function q{a[0] + n * a[1]}. You need to use a valid D expression using symbols a of type Tuple!(int,int) and n of type uint."
This has been fixed a while ago. I added a unittest in http://www.dsource.org/projects/phobos/changeset/2067 to make sure this doesn't regress.