>cabal install
Resolving dependencies...
Configuring haddock-2.3.0...
Preprocessing library haddock-2.3.0...
Preprocessing executables for haddock-2.3.0...
Building haddock-2.3.0...
src\Haddock\Utils.hs:1:13:
Warning: -XPatternSignatures is deprecated: use -XScopedTypeVariables or pragma {-# LANGUAGE ScopedTypeVariables#-} instead
[1 of 7] Compiling Haddock.GHC.Utils ( src\Haddock\GHC\Utils.hs, dist\build\Haddock\GHC\Utils.o )
[3 of 7] Compiling Haddock.Exception ( src\Haddock\Exception.hs, dist\build\Haddock\Exception.o )
src\Haddock\Exception.hs:30:9:
Type constructor `Exception' used as a class
In the instance declaration for `Exception HaddockException'
cabal: Error: some packages failed to install:
haddock-2.3.0 failed during the building phase. The exception was:
exit: ExitFailure 1