Resolving dependencies...
Downloading ImperativeHaskell-1.1.0.0...
Configuring ImperativeHaskell-1.1.0.0...
Building ImperativeHaskell-1.1.0.0...
Preprocessing library ImperativeHaskell-1.1.0.0...
[1 of 4] Compiling Control.Monad.Imperative.Internals ( Control/Monad/Imperative/Internals.hs, dist/build/Control/Monad/Imperative/Internals.o )
[2 of 4] Compiling Control.Monad.Imperative.FunctionFactory ( Control/Monad/Imperative/FunctionFactory.hs, dist/build/Control/Monad/Imperative/FunctionFactory.o )
[3 of 4] Compiling Control.Monad.Imperative.Operators ( Control/Monad/Imperative/Operators.hs, dist/build/Control/Monad/Imperative/Operators.o )

Control/Monad/Imperative/Operators.hs:26:19:
    Duplicate type signatures for `<=.'
    at Control/Monad/Imperative/Operators.hs:26:13-17
       Control/Monad/Imperative/Operators.hs:26:19-23
Failed to install ImperativeHaskell-1.1.0.0
cabal: Error: some packages failed to install:
ImperativeHaskell-1.1.0.0 failed during the building phase. The exception was:
ExitFailure 1