the Config interface should be Applicative, not Monad

this allows for safer alternative uses for it, such as running it on an
empty list of config sources to just get the list of keys it uses.

1 files changed, 16 insertions, 3 deletions

diff --git a/test/Main.hs b/test/Main.hs
index 5c01f64..1af3d9a 100644
--- a/test/Main.hs
+++ b/test/Main.hs
@@ -2,6 +2,7 @@
 {-# LANGUAGE OverloadedStrings #-}
 {-# LANGUAGE DeriveAnyClass #-}
 {-# LANGUAGE TemplateHaskell #-}
+{-# LANGUAGE ApplicativeDo #-}
 module Main (main) where
 
 import Conftrack
@@ -15,6 +16,7 @@ import Test.QuickCheck.Monadic
 import Test.QuickCheck.Instances ()
 import System.Exit (exitFailure, exitSuccess)
 import qualified Data.Text.Encoding as BS
+import Data.List ((\\))
 
 
 data TestFlat = TestType { testFoo :: Text, testBar :: Integer }
@@ -35,9 +37,10 @@ instance Config TestFlat where
     <*> readRequiredValue (Key ["bar"])
 
 instance Config TestNested where
-  readConfig = TestNested
-    <$> readRequiredValue (Key ["foo"])
-    <*> readNested (Key ["nested"])
+  readConfig = do
+    a <- readRequiredValue (Key ["foo"])
+    b <- readNested (Key ["nested"])
+    pure (TestNested a b)
 
 testTypeToTrivial :: TestFlat -> SomeSource
 testTypeToTrivial (TestType foo bar) = mkTrivialSource
@@ -81,6 +84,16 @@ prop_aeson_flat = roundtripVia testTypeToJson
 prop_aeson_nested :: TestNested -> Property
 prop_aeson_nested = roundtripVia nestedToJson
 
+prop_flat_keys :: Property
+prop_flat_keys = monadicIO $ do
+  keys <- run $ configKeysOf @TestFlat
+  assert (null (keys \\ [ Key ["foo"], Key ["bar"] ]))
+
+prop_nested_keys :: Property
+prop_nested_keys = monadicIO $ do
+  keys <- run $ configKeysOf @TestNested
+  assert (null (keys \\ [ Key ["foo"], Key ["nested", "bar"], Key ["nested", "foo"] ]))
+
 -- see quickcheck docs for why this return is here
 return []
 runTests = $quickCheckAll