MonadFail instance for GHC 8.6

[mtolly]

Closes #21

CPP-limited to base 4.9.0.0 and up based on the info here.

[nomeata]

@mtolly, do you have an interest in maybe taking over maintainership of HPDF on hackage?

[dten]

won't compile for me with base-4.10.1.0

Graphics/PDF/Draw.hs:204:27: error:
        • No instance for (Fail.MonadFail (ST s))
            arising from a use of ‘Fail.fail’
        • In the expression: Fail.fail s
          In the second argument of ‘($)’, namely ‘\ _ -> Fail.fail s’
          In the expression: Draw $ \ _ -> Fail.fail s
        |
    204 |     fail s = Draw $ \_ -> Fail.fail s
        |                           ^^^^^^^^^^^

[dten]

works with base-4.11.1.0

ST isn't monad fail until 4.11
https://www.stackage.org/haddock/lts-11.22/base-4.10.1.0/Control-Monad-ST.html#t:ST
https://www.stackage.org/haddock/lts-12.14/base-4.11.1.0/Control-Monad-ST.html#t:ST

suggestion here is also (4,11,0)
https://wiki.haskell.org/MonadFail_Proposal

[mtolly]

Thanks @dten, I've edited the commit with that. Though it looks like #23 would be a better change to use; the MonadFail instance is overkill since it was only used for one failing do pattern.

@nomeata Tbh I probably wouldn't be the best person - I could maybe keep up with basic compiler fixes and that sort of thing but I don't know much of anything about the PDF format internals.

[dten]

That pr has a lot more changes in it. Your change worked and I was easy to verify 👍

[bgohla]

in my view this is the wrong way to go. the reason the original code was actually fine, was that the list is defined to be infinite, so that should be expressed by using, e.g., http://hackage.haskell.org/package/inflist-0.0.1/docs/src/Data-InfList.html#InfList

i've implemented that here: #27

[hsyl20]

Fixed in 1.5.0