Supported GHC 8.8.1

[asr]

GHC 8.8.1-rc1 was announced. In this PR I fixed the compilation with this version of GHC.

Blocking agda/agda#3725.

[robdockins]

I think turning fail into error isn't the right fix in the majority of these cases. We probably actually want to turn most of the functions with a Moand constraint into an Alternative constraint instead and use empty instead of fail. I think this more accurately captures the original intent of the API.
In particular, in the (common, I suspect) case that the container type is Maybe it would continue to return Nothing in cases where elements are not found instead of going to error.

What do you think?

[nad]

Another option would be to use MonadFail.

[asr]

Another option would be to use MonadFail.

This was my first try but I had some problems. Now, I could fix the problems based on the new module Agda/Utils/Fail.hs (thanks @UlfNorell). Note that I updated (force-pushed) the PR.

[robdockins]

This looks like a better fix to me. I'll work on finding some time soon (this weekend probably) to merge this and put up a new release.