On Thu, May 14, 2015 at 9:17 PM, Michael Jones <mike@proclivis.com> wrote:
I kind of think it is some kind of equality constraint but can’t find documentation. Perhaps if I knew what it was called I might succeed in finding something. If it is an equality constraint, please provide a reference if you have one. I did not find anything in a search including GHC, etc.

~ is an equality constraint only in a type constraint (foo :: (x ~ y) => ...). In a pattern, it indicates the pattern matches lazily instead of the usual strict match.

--
brandon s allbery kf8nh                               sine nomine associates
allbery.b@gmail.com                                  ballbery@sinenomine.net
unix, openafs, kerberos, infrastructure, xmonad        http://sinenomine.net