Working on it

app/Main.hs

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+{-# LANGUAGE DeriveAnyClass,
+             DeriveGeneric,
+             DerivingVia,
+             DuplicateRecordFields,
+             LambdaCase,
+             GADTs,
+             NoFieldSelectors,
+             OverloadedRecordDot,
+             RecordWildCards,
+             OverloadedStrings #-}
+module Main (main) where
+
+import WithCli
+import Data.Maybe
+import Effectful ( IOE, (:>), Eff, MonadIO(liftIO), runEff )
+import Effectful.Reader.Static ( runReader, Reader )
+import Data.Yaml
+import GHC.Generics (Generic)
+import Data.Functor
+import System.Environment.XDG.BaseDir
+import Data.HashMap.Lazy (HashMap, insert)
+import System.Environment.XDG.DesktopEntry
+
+data Options = Options {
+     config :: Maybe FilePath,
+     cache :: Maybe FilePath,
+     dmenu :: Bool
+   }
+   deriving (Show, Generic, HasArguments)
+
+data Config a where
+  Config :: { cachePath :: a } -> Config a
+  deriving (Show, Generic, FromJSON, ToJSON)
+
+type Cache = HashMap String Int
+
+data Item = Item { name :: String
+                 , uses :: Int
+                 }
+  deriving (Show, Generic, FromJSON, ToJSON)
+
+defaultCachePath :: IO FilePath
+defaultCachePath = getUserCacheFile "mide" "cache.yaml"
+
+defaultConfigPath :: IO FilePath
+defaultConfigPath = getUserConfigFile "mide" "config.yaml"
+
+type State = (Config FilePath, Cache)
+
+main :: IO ()
+main = withCliModified [ AddShortOption "config" 'c',
+                         AddShortOption "dmenu" 'd',
+                         AddOptionHelp "config" "Point to the file containing yaml for configuration",
+                         AddOptionHelp "cache" "Point to the file containing yaml for cache",
+                         AddOptionHelp "dmenu" "Run in dmenu version"
+                       ]
+                       run
+
+fixConfig :: Config (Maybe FilePath) -> IO (Config FilePath)
+fixConfig Config{..} = maybe (defaultCachePath <&> Config) (pure . Config) cachePath
+
+run :: Options -> IO ()
+run opts =
+  maybe defaultConfigPath pure opts.config >>= \configPath ->
+   decodeFileEither configPath >>= either (const $ Config . pure <$> defaultCachePath) pure >>= fixConfig >>= \config ->
+  (decodeFileEither config.cachePath <&> either mempty ((foldr (\p -> insert p.name p.uses) mempty) :: [Item] -> HashMap String Int)) >>= \cache ->
+  runEff $ runReader (config,cache) (if opts.dmenu then dmenu else normal)
+
+normal :: (Reader State :> es, IOE :> es) => Eff es ()
+normal = liftIO getDirectoryEntriesDefault >>= mapM_ (liftIO . print)
+
+dmenu :: (Reader State :> es, IOE :> es) => Eff es ()
+dmenu = undefined