Fix hlint warnings for hlint v2.1.20 (#1320)

* Apply some hlint suggestions.

* Simplify config parser (to avoid hlint error)

* Reorganize for clarity (and fix hlint error)

* Remove redundant language extension

* Reformat slice more conventionally to avoid hlint bug

* Refactor for clarity (and to avoid hlint error)

* Simplify (and avoid hlint error)

* Fix hlint complaint

src/PostgREST/Types.hs

@@ -91,20 +91,21 @@ instance Ord ProcDescription where
     | otherwise = (name1, des1, args1, rt1, vol1) `compare` (name2, des2, args2, rt2, vol2)
 
 {-|
-  Search a pg procedure by its parameters, since a function can be overloaded the name is not enough to find it.
+  Search a pg procedure by its parameters. Since a function can be overloaded, the name is not enough to find it.
   An overloaded function can have a different volatility or even a different return type.
 -}
 findProc :: QualifiedIdentifier -> S.Set Text -> Bool -> M.HashMap Text [ProcDescription] -> Maybe ProcDescription
 findProc qi payloadKeys paramsAsSingleObject allProcs =
-  let procs = M.lookup (qiName qi) allProcs in
- -- Handle overloaded functions case
-  join $ (case length <$> procs of
-    Just 1 -> headMay -- if it's not an overloaded function then immediatly get the ProcDescription
-    _ -> find (\x ->
-           if paramsAsSingleObject
-             then length (pdArgs x) == 1 -- if the arg is not of json type let the db give the err
-             else payloadKeys `S.isSubsetOf` S.fromList (pgaName <$> pdArgs x))
-  ) <$> procs
+  case M.lookup (qiName qi) allProcs of
+    Nothing     -> Nothing
+    Just [proc] -> Just proc           -- if it's not an overloaded function then immediately get the ProcDescription
+    Just procs  -> find matches procs  -- Handle overloaded functions case
+  where
+    matches proc =
+      if paramsAsSingleObject
+        -- if the arg is not of json type let the db give the err
+        then length (pdArgs proc) == 1
+        else payloadKeys `S.isSubsetOf` S.fromList (pgaName <$> pdArgs proc)
 
 {-|
   Search the procedure parameters by matching them with the specified keys.