Preprocessing executable 'stackage-sandbox' for stackage-cli-0.0.0... [1 of 2] Compiling Paths_stackage_cli ( dist/build/autogen/Paths_stackage_cli.hs, dist/build/stackage-sandbox/stackage-sandbox-tmp/Paths_stackage_cli.o ) [2 of 2] Compiling Main ( main/Sandbox.hs, dist/build/stackage-sandbox/stackage-sandbox-tmp/Main.o ) main/Sandbox.hs:321:46: No instance for (Foldable t0) arising from a use of ‘elem’ The type variable ‘t0’ is ambiguous Note: there are several potential instances: instance Foldable (Const m) -- Defined in ‘Control.Applicative’ instance Foldable (Either a) -- Defined in ‘Data.Foldable’ instance Foldable Data.Functor.Identity.Identity -- Defined in ‘Data.Functor.Identity’ ...plus 8 others In the first argument of ‘flip’, namely ‘elem’ In the second argument of ‘(.)’, namely ‘flip elem "/\\"’ In the first argument of ‘T.takeWhile’, namely ‘(not . flip elem "/\\")’ main/Sandbox.hs:321:51: No instance for (Data.String.IsString (t0 Char)) arising from the literal ‘"/\\"’ The type variable ‘t0’ is ambiguous Note: there is a potential instance available: instance Data.String.IsString [Char] -- Defined in ‘Data.String’ In the second argument of ‘flip’, namely ‘"/\\"’ In the second argument of ‘(.)’, namely ‘flip elem "/\\"’ In the first argument of ‘T.takeWhile’, namely ‘(not . flip elem "/\\")’ cabal: Error: some packages failed to install: stackage-cli-0.0.0 failed during the building phase. The exception was: ExitFailure 1