Resolving dependencies...
Configuring mtl-2.2.1...
Configuring syb-0.6...
Building mtl-2.2.1...
Building syb-0.6...
Configuring text-1.2.2.1...
Installed syb-0.6
Installed mtl-2.2.1
Configuring regex-base-0.93.2...
Building text-1.2.2.1...
Building regex-base-0.93.2...
Installed regex-base-0.93.2
Configuring regex-posix-0.95.2...
Building regex-posix-0.95.2...
Installed regex-posix-0.95.2
Installed text-1.2.2.1
Configuring parsec-3.1.11...
Building parsec-3.1.11...
Installed parsec-3.1.11
Configuring preprocessor-tools-1.0.1...
Building preprocessor-tools-1.0.1...
Installed preprocessor-tools-1.0.1
Configuring interpol-0.1.0...
Building interpol-0.1.0...
Failed to install interpol-0.1.0
Build log ( /home/builder/.cabal/logs/interpol-0.1.0.log ):
cabal: Entering directory '/tmp/cabal-tmp-29642/interpol-0.1.0'
Configuring interpol-0.1.0...
Building interpol-0.1.0...
Preprocessing executable 'interpol' for interpol-0.1.0...
[1 of 1] Compiling Main             ( Main.hs, dist/build/interpol/interpol-tmp/Main.o )

Main.hs:17:38: error:
    • Couldn't match type ‘[Ast]’ with ‘IO [Ast]’
      Expected type: [Ast] -> IO [Ast]
        Actual type: IO [Ast] -> IO [Ast]
    • In the ‘transformer’ field of a record
      In the expression: mempty {transformer = everywhere (mkT trans)}
      In an equation for ‘interpolExt’:
          interpolExt
            = mempty {transformer = everywhere (mkT trans)}
            where
                trans :: Ast -> Ast
                trans (Single {item = tok@(Token {tag = StringLit, val = s})})
                  = let ... in Single (tok {val = s'})
                trans ast = ast
                ti = tail . init
                identRE = "\\{[A-z_][A-z0-9_]*}"
                ....
cabal: Leaving directory '/tmp/cabal-tmp-29642/interpol-0.1.0'
cabal: Error: some packages failed to install:
interpol-0.1.0 failed during the building phase. The exception was:
ExitFailure 1