style: prefer <> over ++

Author: drlkf

.hlint.yaml

@@ -1 +1,2 @@
 - warn: {lhs: map, rhs: fmap, name: Use fmap}
+- warn: {lhs: a ++ b, rhs: a <> b, name: Use <>}

AGENTS.md

@@ -13,7 +13,7 @@ CI (`.github/workflows/ci.yml`) runs all of the above; keep it green.
 
 ## Style
 
-- `fmap` over `map`
+- `fmap` over `map`, `<>` over `++` (enforced by hlint)
 - curried constraints: `Read a => Ord a => a`, not `(Read a, Ord a) => a`;
   not enforced by tooling; constraint aliases such as `CLIEffects` stay tuples
 - `-Wredundant-constraints` on: only add `Show e` for `throwError` where needed

src/Data/CLI/Args.hs

@@ -47,7 +47,7 @@ argParser cmdParser =
           ( short 'l'
               <> long "log-level"
               <> metavar "LEVEL"
-              <> help ("Log level: " ++ intercalate ", " (fmap fst logLevels))
+              <> help ("Log level: " <> intercalate ", " (fmap fst logLevels))
           )
       )
     <*> switch (short 'd' <> long "debug" <> help "Enable debug output (overruled by -l)")

src/Data/Error/CLI.hs

@@ -13,8 +13,8 @@ data CLIError
 
 -- | @since 0.1.0.0
 displayCLIError :: CLIError -> String
-displayCLIError (InputError s) = "input error: " ++ s
-displayCLIError (NotFoundError s) = "not found: " ++ s
-displayCLIError (NotImplemented s) = "not implemented: " ++ s
+displayCLIError (InputError s) = "input error: " <> s
+displayCLIError (NotFoundError s) = "not found: " <> s
+displayCLIError (NotImplemented s) = "not implemented: " <> s
 displayCLIError (UserCanceled Nothing) = "user canceled"
-displayCLIError (UserCanceled (Just s)) = "user canceled: " ++ s
+displayCLIError (UserCanceled (Just s)) = "user canceled: " <> s

src/Effectful/CLI/IO.hs

@@ -50,7 +50,7 @@ printLines = printOutput . unlines
 -- | @since 0.1.0.0
 prompt :: IOE :> es => Maybe String -> Eff es String
 prompt p = liftIO $ do
-  hPutStr stderr (fromMaybe "" p ++ "> ")
+  hPutStr stderr (fromMaybe "" p <> "> ")
   hFlush stderr
   getLine
 
@@ -91,7 +91,7 @@ chooseItem
   :: Error CLIError :> es
   => IOE :> es
   => String -> [String] -> (a -> [String]) -> [a] -> Eff es a
-chooseItem name _ _ [] = throwError (NotFoundError ("no item found for " ++ name))
+chooseItem name _ _ [] = throwError (NotFoundError ("no item found for " <> name))
 chooseItem _ _ _ [x] = pure x
 chooseItem name headers row xs = do
   let hs = "#" : headers

src/Effectful/CLI/Sleep.hs

@@ -34,6 +34,6 @@ sleep n = do
 -- | @since 0.1.0.0
 sleepUntil :: IOE :> es => Logger :> es => LocalTime -> Eff es ()
 sleepUntil t = do
-  logInfoN (T.pack ("sleeping until " ++ formatTime defaultTimeLocale "%R" t))
+  logInfoN (T.pack ("sleeping until " <> formatTime defaultTimeLocale "%R" t))
   now <- getLocalTime
   sleep . ceiling . nominalDiffTimeToSeconds $ diffLocalTime t now