MonadFail proposal

[xaverdh]

This does the necessary changes to make yi-core compile with ghc 8.6, implementing the monad fail proposal.

[xaverdh]

Maybe someone with more knowledge of the code can tell if the marks in 6f0b1c0 are expected to be there (in which case this should be doing the right thing; erroring out), or not.
Something similar appears to be going on in Yi.Search here for example, but I understand the assumptions there even less.

[xaverdh]

The Hoogle part appears to be unused and in a bad shape in general. As it is, it would crash on you more or less immediately. I just did the bare minimum necessary to make it compile, but it should probably be reworked / dropped?

[jhance]

Since this has been waiting forever and not received any review, I'm going to play with it a bit, if it needs any changes I'll do them myself.

[xnox]

Is this related?

src/Parser/Incremental.hs:185:5-8: error:
    ‘fail’ is not a (visible) method of class ‘Monad’
    |
185 |     fail _message = Empt
    |     ^^^^
Haddock coverage:
Haddock failed (no modules?), refusing to create empty documentation package.

[xaverdh]

Is this related?

src/Parser/Incremental.hs:185:5-8: error:
    ‘fail’ is not a (visible) method of class ‘Monad’
    |
185 |     fail _message = Empt
    |     ^^^^
Haddock coverage:
Haddock failed (no modules?), refusing to create empty documentation package.

Yes since ghc 8.8the Monad class no longer has fail a method (my pr was written when ghc 8.6 was the newest release).
Will need to be fixed on top of this pr.

[xnox]

Ubuntu has removed yi from the Ubuntu Archive and will no longer ship it, as it fails to build from source with current 8.8.3 ghc + upgraded dependencies.