I'm trying to install the newest version of Heist, but errors-1.3.1 which is a dependency fails to install. Any suggestions for how to get past this?
$ cabal install errors-1.3.1
Resolving dependencies...
Configuring errors-1.3.1...
Building errors-1.3.1...
Preprocessing library errors-1.3.1...
[1 of 5] Compiling Data.EitherR ( Data/EitherR.hs, dist/build/Data/EitherR.o )
[2 of 5] Compiling Control.Error.Util ( Control/Error/Util.hs, dist/build/Control/Error/Util.o )
Control/Error/Util.hs:74:10:
Could not deduce (Monad m) arising from a use of `fmap'
from the context (Functor m)
bound by the type signature for
fmapRT :: Functor m => (a -> b) -> EitherT l m a -> EitherT l m b
at Control/Error/Util.hs:74:1-13
Possible fix:
add (Monad m) to the context of
the type signature for
fmapRT :: Functor m => (a -> b) -> EitherT l m a -> EitherT l m b
In the expression: fmap
In an equation for `fmapRT': fmapRT = fmap
cabal: Error: some packages failed to install:
errors-1.3.1 failed during the building phase. The exception was:
ExitFailure 1
I fixed this in the latest errors, which is 1.4.1 (1.4.0 has a mistake where I don't export the EitherT and MaybeT types). I've added upper bounds on the either dependency this time to prevent it happening in the future.