Add many-try test

parsec.cabal

@@ -114,6 +114,7 @@ test-suite parsec-tests
         Bugs.Bug6
         Bugs.Bug9
         Bugs.Bug35
+        Bugs.Bug179
         Features
         Features.Feature80
         Features.Feature150

test/Bugs.hs

@@ -9,10 +9,12 @@ import qualified Bugs.Bug2
 import qualified Bugs.Bug6
 import qualified Bugs.Bug9
 import qualified Bugs.Bug35
+import qualified Bugs.Bug179
 
 bugs :: [TestTree]
 bugs = [ Bugs.Bug2.main
        , Bugs.Bug6.main
        , Bugs.Bug9.main
        , Bugs.Bug35.main
+       , Bugs.Bug179.tests
        ]

test/Bugs/Bug179.hs

+
+module Bugs.Bug179
+       ( tests
+       ) where
+
+import Control.Applicative (Alternative (..), liftA2, (<|>))
+import Test.Tasty ( testGroup, TestTree )
+import Test.Tasty.HUnit
+
+import qualified Control.Applicative
+import qualified Text.Parsec as P
+import qualified Text.Parsec.String as P
+
+tests :: TestTree
+tests = testGroup "many try (#179)"
+    [ testCase "manyDefault" $ examples parser1
+    , testCase "C.Applicative" $ examples parser2
+    , testCase "Parsec" $ examples parser3
+    ]
+ where
+    examples p = do
+        res1 <- parseString p $ unlines ["   ", "    ", "foo"]
+        res1 @?= "foo\n"
+
+        res2 <- parseString p $ unlines ["bar"]
+        res2 @?= "bar\n"
+
+        res3 <- parseString p $ unlines ["   ", "    ", "  foo"]
+        res3 @?= "  foo\n"
+
+        res4 <- parseString p $ unlines ["  bar"]
+        res4 @?= "  bar\n"
+
+    parseString :: P.Parser String -> String -> IO String
+    parseString p input =
+      case P.parse p "" input of
+        Left err -> assertFailure $ show err
+        Right str -> return str
+
+parser1 :: P.Parser String
+parser1 = emptyLines *> P.getInput where
+    emptyLines :: P.Parser String
+    emptyLines = manyDefault $ P.try $ P.skipMany (P.satisfy (== ' ')) *> P.char '\n'
+
+parser2 :: P.Parser String
+parser2 = emptyLines *> P.getInput where
+    emptyLines :: P.Parser String
+    emptyLines = Control.Applicative.many $ P.try $ P.skipMany (P.satisfy (== ' ')) *> P.char '\n'
+
+parser3 :: P.Parser String
+parser3 = emptyLines *> P.getInput where
+    emptyLines :: P.Parser String
+    emptyLines = P.many $ P.try $ P.skipMany (P.satisfy (== ' ')) *> P.char '\n'
+
+-- many's default definition
+manyDefault :: Alternative f => f a -> f [a]
+manyDefault v = many_v
+    where
+    many_v = some_v <|> pure []
+    some_v = liftA2 (:) v many_v