diff --git a/cli-setup.cabal b/cli-setup.cabal
--- a/cli-setup.cabal
+++ b/cli-setup.cabal
@@ -1,6 +1,6 @@
 cabal-version: 1.18
 name: cli-setup
-version: 0.2.0.3
+version: 0.2.0.4
 license: BSD3
 license-file: LICENSE
 copyright: Copyright: (c) 2018 Vanessa McHale
@@ -35,7 +35,7 @@
     default-language: Haskell2010
     ghc-options: -Wall
     build-depends:
-        base >=4.8 && <5,
+        base >=4.9 && <5,
         directory -any,
         process >=1.4.0.0,
         bytestring -any,
diff --git a/src/Distribution/CommandLine.hs b/src/Distribution/CommandLine.hs
--- a/src/Distribution/CommandLine.hs
+++ b/src/Distribution/CommandLine.hs
@@ -28,8 +28,8 @@
     case h of
         Just h' -> do
             proceed <- doesDirectoryExist (h' ++ "/.config/thefuck/rules")
-            bool (pure ()) (writeFile (h' ++ "/.config/thefuck/rules/optparse-applicative.py") rules) proceed
-        Nothing -> pure ()
+            bool mempty (writeFile (h' ++ "/.config/thefuck/rules/optparse-applicative.py") rules) proceed
+        Nothing -> mempty
 
 -- | Add a line exporting the modified @MANPATH@ to the user's @bashrc@, if it
 -- does not exist already.
@@ -45,7 +45,7 @@
                 unless ("#manpath updated by cli-setup" `elem` lines config && length config > 0)
                     (appendFile bashRc "\n#manpath updated by cli-setup\nexport MANPATH=~/.local/share:$MANPATH\n" >>
                     void (readCreateProcessWithExitCode (shell $ "MANPATH=" ++ x ++ "/.local/share mandb") ""))
-        Nothing -> pure ()
+        Nothing -> mempty
 
 -- | As an example, if your source tarball contains a file @man/madlang.1@ you
 -- could use
@@ -61,7 +61,7 @@
             let manPath = x ++ "/.local/share/man/man1"
             createDirectoryIfMissing True manPath
             writeFile (manPath ++ "/" ++ p') =<< readFile p
-        Nothing -> pure ()
+        Nothing -> mempty
 
 -- | Add a line to the user's @bashrc@ so that command-line completions work
 -- automatically.
@@ -75,4 +75,4 @@
             config <- readFile bashRc
             unless (("# Added for " ++ exeName) `elem` lines config)
                 (appendFile bashRc ("\n# Added for " ++ exeName ++ "\neval \"$(" ++ exeName ++ " --bash-completion-script " ++ exeName ++ ")\"\n"))
-        Nothing -> pure ()
+        Nothing -> mempty