Display empty results and no results differently

src/Propa/Prolog/Debug.hs

@@ -12,7 +12,12 @@ import           Propa.Prolog.Parse
 import           Propa.Prolog.Unify
 
 parseAndRun :: T.Text -> T.Text -> IO ()
-parseAndRun dbText statsText = T.putStrLn $ either id id $ do
+parseAndRun dbText statsText = T.putStrLn $ case results of
-  db <- parseDb "<input>" dbText
+  Left e   -> e
-  stats <- parseStats "<input>" statsText
+  Right [] -> "No."
-  pure $ T.intercalate "\n" $ map displayResult $ run db stats
+  Right rs -> T.intercalate "\n" rs
+  where
+    results = do
+      db <- parseDb "<input>" dbText
+      stats <- parseStats "<input>" statsText
+      pure $ map displayResult $ run db stats

src/Propa/Prolog/Display.hs

@@ -61,8 +61,9 @@ displayDefs :: [Def T.Text] -> T.Text
 displayDefs = T.intercalate "\n" . map displayDef
 
 displayResult :: Map.Map T.Text (Term T.Text) -> T.Text
-displayResult
+displayResult m | Map.null m = "Yes."
+displayResult m
   = T.intercalate "\n"
-  . map (\(k, v) -> k <> " = " <> displayTerm v)
+  $ map (\(k, v) -> k <> " = " <> displayTerm v)
-  . filter (\(k, v) -> v /= TVar k)
+  $ filter (\(k, v) -> v /= TVar k)
-  . Map.assocs
+  $ Map.assocs m