18 Nov
2015
18 Nov
'15
2:44 a.m.
On Wed, Nov 18, 2015 at 5:15 AM, Marcin Mrotek
arbitrarily. But the second law is a hopeless case. You would need to pick one element of a pair, plug it into a function that repeats the argument, and somehow get back the other element that you've already dropped.
Concluding, either I'm sorely mistaken or there indeed isn't a Monad instance for Pair.
Not quite sorely mistaken but there is a glitch in the logic of what you wrote when you returned from join to bind. You might want to try writing out a test instance in full and re-checking the second law. -- Kim-Ee