Add ‘Word8’ instance of ‘ShowToken’

Text/Megaparsec/Error.hs

@@ -36,6 +36,7 @@ where
 
 import Control.DeepSeq
 import Control.Exception
+import Data.Char (chr)
 import Data.Data (Data)
 import Data.List (intercalate)
 import Data.List.NonEmpty (NonEmpty (..))
@@ -44,6 +45,7 @@ import Data.Semigroup
 import Data.Set (Set)
 import Data.Typeable (Typeable)
 import Data.Void
+import Data.Word (Word8)
 import GHC.Generics
 import Prelude hiding (concat)
 import qualified Data.List.NonEmpty as NE
@@ -199,6 +201,9 @@ class ShowToken a where
 instance ShowToken Char where
   showTokens = stringPretty
 
+instance ShowToken Word8 where
+  showTokens = stringPretty . fmap (chr . fromIntegral)
+
 -- | The type class defines how to print custom data component of
 -- 'ParseError'.
 --

tests/Text/Megaparsec/ErrorSpec.hs

@@ -7,6 +7,7 @@ import Data.List (isInfixOf, isSuffixOf)
 import Data.List.NonEmpty (NonEmpty (..))
 import Data.Monoid
 import Data.Void
+import Data.Word (Word8)
 import Test.Hspec
 import Test.Hspec.Megaparsec.AdHoc ()
 import Test.QuickCheck
@@ -173,6 +174,13 @@ spec = do
     it "shows control characters in long strings property"
       (f "{\n" "\"{<newline>\"")
 
+  describe "showTokens (Word8 instance)" $
+    it "basically works" $ do
+      -- NOTE Currently the Word8 instance is defined via Char intance, so
+      -- the testing is rather swallow.
+      let ts = NE.fromList [10,48,49,50] :: NonEmpty Word8
+      showTokens ts `shouldBe` "\"<newline>012\""
+
   describe "parseErrorPretty" $ do
     it "shows unknown ParseError correctly" $
       parseErrorPretty (mempty :: PE) `shouldBe` "1:1:\nunknown parse error\n"