fail is moving out of Monad and into it's own MonadFail class.
This will be enforced in GHC 8.8 (I think).
base-compat/base-compat-batteries 0.11.0 have adapted to this,
and are approaching stackage nightly
(https://github.com/commercialhaskell/stackage/issues/4802).
hledger is now ready to build with base-compat-batteries 0.11.0, once
all of our deps do (eg aeson). We are still compatible with the older
0.10.x and GHC 7.10.3 as well.
For now we are using both fails:
- new fail (from Control.Monad.Fail), used in our parsers, imported
via base-compat-batteries Control.Monad.Fail.Compat to work with
older GHC versions.
- old fail (from GHC.Base, exported by Prelude, Control.Monad,
Control.Monad.State.Strict, Prelude.Compat, ...), used in easytest's
Test, since I couldn't find their existing fail implementation to update.
To reduce (my) confusion, these are imported carefully, consistently,
and qualified everywhere as Fail.fail and Prelude.fail, with clashing
re-exports suppressed, like so:
import Prelude hiding (fail)
import qualified Prelude (fail)
import Control.Monad.State.Strict hiding (fail)
import "base-compat-batteries" Prelude.Compat hiding (fail)
import qualified "base-compat-batteries" Control.Monad.Fail.Compat as Fail
For Data/Dates.hs in particular:
- Changed `SimpleTextParser` to `TextParser m` for all parsers
- Changed `string` to the case-insensitive `string'` to match the
behaviour of `T.toLower` found in `parsePeriodExpr`
- export `periodexprp` for "direct" use
base-compat-batteries provides the same API across more ghc versions
than base-compat does, at the cost of more dependencies. Eg it exports
Prelude.Compat ((<>)) with ghc 7.10/base 4.8, which we expect.
My belief is that several of our deps already require it so the added
cost is not too great. We should probably go back to base-compat when
possible though, eg when we stop supporting ghc 7.10.
The new version of our package set apparently contains both base-compat and
base-compat-batteries in its transitive closure. This breaks the doctest suite,
which just imports everything into scope when the tests are run, thereby making
module names like Prelude.Compat ambiguous.
