Widen support to GHC-7.4...GHC-8.8

[phadej]

• GHC-8.8 is straight-forward MONAD_NO_FAIL fix
• GHC-7.4 + GHC-7.6 is trickier
  • motivation We'd like to use prettyprinter in trifecta and criterion, and it would be nice to keep support for older GHCs (especially for criterion). In this case the price is not that big.
  • no LambdaCase
  • and AutoDeriveTypeable -> DataDeriveTypeable
  • there's small problem, pgp-wordlist is base >=4.6 (not base >= 4.5), but with --allow-older=pgp-wordlist:base it compiles fine.

There are few follow-ups which I'd like to do:

• extend pgp-wordlist support to GHC-7.4 too (should be simple)
• use haskell-ci for CI, so we can test old GHCs (and new!)
• split benchmarks into own package, because if/when criterion would depend on prettyprint there would be nasty package loop. Similar thing is done in e.g. Convert to cabal.project haskell/containers#626

cc @RyanGlScott

[phadej]

Looks like travis is disabled for this and quchen/pgp-wordlist#3

[RyanGlScott]

I certainly appreciate the work that goes into PRs like this. Do note that if your eventual goal is to get criterion to use prettyprinter, the real challenge is going to be optparse-applicative (on top of which criterion builds its pretty-printed CLI --help output), which supports all the way back to GHC 7.0. (See also pcapriotti/optparse-applicative#273).

[phadej]

In fact, it’s simple-ish to extend support back to 7.0 too; one would need to make defaults/Generics optional. Or use generic-deriving. I’m happy to walk that path. Having wide GHC support is a ”there are no type system magic” indicator. Which I value for basic libs, like pretty printing. OTOH it cames with some CPP cost; but not terrible. With haskell-ci it will be easy to setup CI even in that case.

…

On 6 May 2019, at 14.07, Ryan Scott ***@***.***> wrote: I certainly appreciate the work that goes into PRs like this. Do note that if your eventual goal is to get criterion to use prettyprinter, the real challenge is going to be optparse-applicative (on top of which criterion builds its pretty-printed CLI --help output), which supports all the way back to GHC 7.0. (See also pcapriotti/optparse-applicative#273). — You are receiving this because you authored the thread. Reply to this email directly, view it on GitHub, or mute the thread.

[phadej]

ping @quchen

[quchen]

PGP-Wordlist is only a test dependency, and not an important one at that. I think it can easily be removed.