make osp :: QuasiQuoter valid as a pattern

[lawbel]

Resolves issue #205

Notes:

• Alternative to the quote [p|...|] is something like

  viewP (appE (varE '(==)) (lift osp')) (conP 'True [])

  Although this may then need CPP to adjust for conP gaining an extra argument in template-haskell v2.18.0.0. Not sure which GHC version this changed in, but it's due to the ability to bind a type parameter with a constructor like

  foo :: Maybe a -> String
  foo (Just @a x) = "just"

  Given that, I thought the quote would be clearer. I'm assuming it should be easier to maintain as well, as it should avoid the need to update with any TH changes?

• TemplateHaskellQuotes and ViewPatterns extensions both go back to GHC v6.x which should be plenty for back-compat?

• Any other changes that should be made? Add some suitable tests?

• Should we change the other QuasiQuoters as well? Make similar changes to osstr and pstr?

[Bodigrim]

I think filepath should define just

osp :: QuasiQuoter
osp = OS.osstr

pstr :: QuasiQuoter
pstr = OS.osstr

while the actual quasiquoter to be improved in https://github.com/haskell/os-string.

[hasufell]

I think filepath should define just

osp :: QuasiQuoter
osp = OS.osstr

pstr :: QuasiQuoter
pstr = OS.osstr

while the actual quasiquoter to be improved in https://github.com/haskell/os-string.

We run isValid at compile time here, which we don't in the osstr quasiquoters.

[hasufell]

@lawbel we probably want this patch for os-string as well

[lawbel]

@hasufell sorry I wasn't able to look at this over the weekend. I see you've done a PR for os-string as well, so I guess this is all done then? I appreciate the help in getting this over the line 😄