Beginner-friendly syntax in decodeJsonTuple (#76)

* Decode Tuple as Array instead of List internally

Author: milesfrain

src/Data/Argonaut/Decode/Class.purs

@@ -2,6 +2,7 @@ module Data.Argonaut.Decode.Class where
 
 import Prelude
 
+import Control.Apply (lift2)
 import Data.Argonaut.Core (Json, isNull, caseJsonNull, caseJsonBoolean, caseJsonNumber, caseJsonString, toArray, toObject, toString, stringify)
 import Data.Array as Arr
 import Data.Array.NonEmpty (NonEmptyArray)
@@ -10,7 +11,7 @@ import Data.Bifunctor (lmap, rmap)
 import Data.Either (Either(..), note)
 import Data.Identity (Identity(..))
 import Data.Int (fromNumber)
-import Data.List (List(..), (:), fromFoldable)
+import Data.List (List, fromFoldable)
 import Data.List as L
 import Data.List.NonEmpty (NonEmptyList)
 import Data.List.NonEmpty as NEL
@@ -41,10 +42,11 @@ instance decodeJsonMaybe :: DecodeJson a => DecodeJson (Maybe a) where
     | otherwise = Just <$> decodeJson j
 
 instance decodeJsonTuple :: (DecodeJson a, DecodeJson b) => DecodeJson (Tuple a b) where
-  decodeJson j = decodeJson j >>= f
-    where
-    f (a : b : Nil) = Tuple <$> decodeJson a <*> decodeJson b
-    f _ = Left "Couldn't decode Tuple"
+  decodeJson j = do
+    decoded <- decodeJson j
+    case decoded of
+      [a, b] -> lift2 Tuple (decodeJson a) (decodeJson b)
+      _ -> Left "Couldn't decode Tuple"
 
 instance decodeJsonEither :: (DecodeJson a, DecodeJson b) => DecodeJson (Either a b) where
   decodeJson json =