optimize test runner

test/Main.hs

@@ -3,7 +3,6 @@
 module Main (main) where
 
 import Control.Monad (unless)
-import qualified Data.List as List
 import Data.Map.Strict (Map)
 import Data.Text (Text)
 import qualified Data.Text.IO as TIO
@@ -131,14 +130,16 @@ testArrayKey1 kv =
     expected = [1, 2, 3]
     actual = kv ^.. mapAt "array" . valueAt "key1" . _List . traverse . _Integer
 
-makeFolder :: Table -> (String, Bool) -> (Table -> Test) -> (String, Bool)
-makeFolder kv (output, isPassed) test =
+makeStep :: Table -> (Table -> Test) -> (ShowS, Bool) -> (ShowS, Bool)
+makeStep kv test (f, allPassed) =
   let result = runTest (test kv)
-   in (output <> "\n" <> resultToString result, isPassed && resultIsPassed result)
+   in (showString (resultToString result) . showChar '\n' . f, resultIsPassed result && allPassed)
 
 runTests :: Table -> (String, Bool)
-runTests kv = List.foldl' (makeFolder kv) (mempty, True) tests
+runTests kv = (buildString mempty, passed)
   where
+    step = makeStep kv
+    (buildString, passed) = foldr step (mempty, True) tests
     tests =
       [ testTableKey,
         testTableZoo,
@@ -161,5 +162,5 @@ main :: IO ()
 main = do
   ex <- readTomlFile "./example/example-v0.4.0.toml"
   let (output, passed) = runTests ex
-  putStrLn output
+  putStr output
   unless passed exitFailure