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Answer : Resync your project gradle files to add the app module through Gradle In the root folder of your project, open the settings.gradle file for editing. Cut line include ':app' from the file. On Android Studio, click on the File Menu, and select Sync Project with Gradle files . After synchronisation, paste back line include ':app' to the settings.gradle file. Re-run Sync Project with Gradle files again. never mind, i changed the name in settings.gradle and synced and then changed it back and synced again and it inexplicably worked this time. Try to delete the app.iml in your project directory and restart android studio

Answer : These general steps were helpful for me to resolve similar issues: Use Hoogle or Stackage to find the package where the module resides Note that Hoogle and Stackage are case-sensitive . Looking up Data.Map in Hoogle yields a list similar to the one below. Stackage has a slightly different style, but the basics are the same (mostly because it also uses Hoogle for lookup). The lines in green under the result headings show the name(s) of the containing (1) package(s) (in small caps) and (2) module(s) (capitalized). Open project-name.cabal in project root and add required package under build-depends: library hs-source-dirs: src build-depends: base >= 4.7 && < 5 , containers exposed-modules: Lib Issue stack build to download and build dependencies (or stack ghci if you plan to use it in the REPL) The reason you can import Data.Char and Data.List is that they are part of the package base , which is included with GHC and is always...