Resolving dependencies...
Configuring mtl-2.2.1...
Configuring syb-0.6...
Building syb-0.6...
Building mtl-2.2.1...
Installed syb-0.6
Configuring haskell-src-1.0.2.0...
Installed mtl-2.2.1
Building haskell-src-1.0.2.0...
Installed haskell-src-1.0.2.0
Configuring htags-1.0...
Building htags-1.0...
Failed to install htags-1.0
Build log ( /home/builder/.cabal/logs/htags-1.0.log ):
cabal: Entering directory '/tmp/cabal-tmp-20781/htags-1.0'
Configuring htags-1.0...
Building htags-1.0...
Preprocessing executable 'htags' for htags-1.0...
[1 of 1] Compiling Main             ( src/htags.hs, dist/build/htags/htags-tmp/Main.o )

src/htags.hs:7:1: error:
    Failed to load interface for ‘Tag’
    Perhaps you meant Bag (needs flag -package-key ghc-8.0.1.20161018)
    Use -v to see a list of the files searched for.

src/htags.hs:8:1: error:
    Failed to load interface for ‘GenTags’
    Use -v to see a list of the files searched for.
cabal: Leaving directory '/tmp/cabal-tmp-20781/htags-1.0'
cabal: Error: some packages failed to install:
htags-1.0 failed during the building phase. The exception was:
ExitFailure 1