tree 818c2bdde21e478fce717310edec4590265d1cb7
parent 6baf26ea74247a0bed5f0b52d13bc3ef1c931204
author Behdad Esfahbod <behdad@behdad.org> 1387447010 -0500
committer Behdad Esfahbod <behdad@behdad.org> 1387448873 -0500

[merge] Use NotImplemented as a singleton meaning "doesn't have"

And cleanup recalculate, so we don't accidentally mess something
that is NOT recalculated.