You are probably using GHC 7.10. With this, you will need any data type to be an instance of applicative and functor for it to be an instance of Monad. However, I don't see a version 1.0.0 for said package. See the below link for more information. You might try your luck asking the maintainer for a fix for this. Or you can copy this locally, make those changes yourself and see how it goes. https://ghc.haskell.org/trac/ghc/wiki/Migration/7.10 On Thu, Dec 3, 2015 at 5:24 PM, wrote:

Hello, what's wrong (see below)???? Thank you in advance, Maurizio

C:\Documents and Settings\xxx1>cabal install FileSystem Resolving dependencies... cabal: Could not resolve dependencies: trying: FileSystem-1.0.0 (user goal) next goal: bytestring (dependency of FileSystem-1.0.0) rejecting: bytestring-0.10.6.0/installed-3a6..., 0.10.6.0, 0.10.4.1, 0.10.4.0, 0.10.2.0, 0.10.0.2, 0.10.0.1, 0.10.0.0 (conflict: FileSystem => bytestring==0.9.*) trying: bytestring-0.9.2.1 trying: directory-1.2.2.0/installed-678... (dependency of FileSystem-1.0.0) next goal: Win32 (dependency of directory-1.2.2.0/installed-678...) rejecting: Win32-2.3.1.0/installed-071... (conflict: bytestring==0.9.2.1, Win32 => bytestring==0.10.6.0/installed-3a6...) rejecting: Win32-2.3.1.0, 2.3.0.2, 2.3.0.1, 2.3.0.0, 2.2.2.0, 2.2.1.0, 2.2.0.2, 2.2.0.1, 2.2.0.0, 2.1.0.0, 2.1 (conflict: directory => Win32==2.3.1.0/installed-071...) Dependency tree exhaustively searched.

C:\Documents and Settings\xxx1>cabal install FileSystem --allow-newer Resolving dependencies... Downloading FileSystem-1.0.0... Configuring FileSystem-1.0.0... Building FileSystem-1.0.0... Preprocessing library FileSystem-1.0.0... [1 of 9] Compiling System.FileSystem.Utils ( System\FileSystem\Utils.hs, dist\bu ild\System\FileSystem\Utils.o ) [2 of 9] Compiling System.FileSystem.Types ( System\FileSystem\Types.hs, dist\bu ild\System\FileSystem\Types.o )

System\FileSystem\Types.hs:123:82: No instance for (Applicative (FST m)) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (Monad (FST m))

System\FileSystem\Types.hs:123:89: No instance for (Applicative (FST m)) arising from the 'deriving' clause of a data type declaration Possible fix: use a standalone 'deriving instance' declaration, so you can specify the instance context yourself When deriving the instance for (MonadIO (FST m)) Failed to install FileSystem-1.0.0 cabal: Error: some packages failed to install: FileSystem-1.0.0 failed during the building phase. The exception was: ExitFailure 1

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