Add Monad instances to (,,) a b and (,,,) a b c
Original discussion: https://mail.haskell.org/pipermail/libraries/2017-March/thread.html#27919
Thank you for your contribution to GHC!
Please take a few moments to verify that your commits fulfill the following:
- are either individually buildable or squashed
have commit messages which describe what they do
(referring to Notes and tickets using
#NNNNsyntax when appropriate)
- [v] have added source comments describing your change. For larger changes you likely should add a Note and cross-reference it from the relevant places.
- add a testcase to the testsuite.
If you have any questions don't hesitate to open your merge request and inquire
in a comment. If your patch isn't quite done yet please do add prefix your MR