I've had rebuild `yesod-bin` using same snapshot as in project, which was

selected as 6.27.  Otherwise `yesod devel` reported an error about compiler

version mismatch.  But default compiler is GHC 8, you're right.

I was able to resolve this doing `stack install --resolver=6.27` using sources

from Git HEAD and removing `yesod` binary already installed in

~/.stack/snapshots/<arch>/lts-6.27/7.10.3/bin.

Thanks.