Resolving dependencies...
Configuring split-0.2.3.1...
Building split-0.2.3.1...
Installed split-0.2.3.1
Downloading libroman-3.0.1...
Configuring libroman-3.0.1...
Building libroman-3.0.1...
Failed to install libroman-3.0.1
Build log ( /home/builder/.cabal/logs/libroman-3.0.1.log ):
cabal: Entering directory '/tmp/cabal-tmp-28265/libroman-3.0.1'
Configuring libroman-3.0.1...
Building libroman-3.0.1...
Preprocessing library libroman-3.0.1...
[1 of 2] Compiling Data.Roman       ( src/Data/Roman.hs, dist/build/Data/Roman.o )

src/Data/Roman.hs:35:5: error:
    • Constraint ‘Roman r’ in the type of ‘fromRoman’
        constrains only the class type variables
      Use ConstrainedClassMethods to allow it
    • When checking the class method:
        fromRoman :: forall r.
                     Roman r =>
                     forall b. (Roman r, Integral b) => r -> b
      In the class declaration for ‘Roman’
cabal: Leaving directory '/tmp/cabal-tmp-28265/libroman-3.0.1'
cabal: Error: some packages failed to install:
libroman-3.0.1 failed during the building phase. The exception was:
ExitFailure 1