Yay! Deadlock problem has finally been solved!

[Lucu.git] / Network / HTTP / Lucu / Parser.hs

diff --git a/Network/HTTP/Lucu/Parser.hs b/Network/HTTP/Lucu/Parser.hs
index 3fa4c150e669dd088112efaf4f7f457fb36add83..0d33a858a6b44362abf8668bc26974fcc5c737fa 100644 (file)
--- a/Network/HTTP/Lucu/Parser.hs
+++ b/Network/HTTP/Lucu/Parser.hs
@@ -1,6 +1,7 @@
 module Network.HTTP.Lucu.Parser
     ( Parser(..)
-    , parse     -- Parser a -> ByteString -> Maybe (a, ByteString)
+    , ParserResult(..)
+    , parse     -- Parser a -> ByteString -> ParserResult a
     , anyChar   -- Parser Char
     , satisfy   -- (Char -> Bool) -> Parser Char
     , char      -- Char -> Parser Char
@@ -26,36 +27,39 @@ import qualified Data.ByteString.Lazy.Char8 as B
 import           Data.ByteString.Lazy.Char8 (ByteString)
 
 data Parser a = Parser {
-      runParser :: State ByteString (Maybe a)
+      runParser :: State ByteString (ParserResult a)
     }
 
+data ParserResult a = Success a
+                    | IllegalInput -- 受理出來ない入力があった
+                    | ReachedEOF   -- 限界を越えて讀まうとした
+
 
 --  (>>=) :: Parser a -> (a -> Parser b) -> Parser b
 instance Monad Parser where
     p >>= f = Parser $ do saved  <- get -- 失敗した時の爲に状態を保存
                           result <- runParser p
                           case result of
-                            Just a  -> runParser (f a)
-                            Nothing -> do put saved -- 状態を復歸
-                                          return Nothing
-    return = Parser . return . Just
-    fail _ = Parser $ return Nothing
+                            Success a    -> runParser (f a)
+                            IllegalInput -> do put saved -- 状態を復歸
+                                               return IllegalInput
+                            ReachedEOF   -> return ReachedEOF
+    return = Parser . return . Success
+    fail _ = Parser $ return IllegalInput
 
 
-parse :: Parser a -> ByteString -> Maybe (a, ByteString)
-parse p input = case runState (runParser p) input of
-                  (Just a , input') -> Just (a, input')
-                  (Nothing, _     ) -> Nothing
+parse :: Parser a -> ByteString -> (ParserResult a, ByteString)
+parse p input = runState (runParser p) input
 
 
 anyChar :: Parser Char
 anyChar = Parser $ do input <- get
                       if B.null input then
-                          return Nothing
+                          return ReachedEOF
                         else
                           do let c = B.head input
                              put (B.tail input)
-                             return (Just c)
+                             return (Success c)
 
 
 satisfy :: (Char -> Bool) -> Parser Char
@@ -79,9 +83,10 @@ infixr 0 <|>
 f <|> g = Parser $ do saved  <- get -- 状態を保存
                       result <- runParser f
                       case result of
-                        Just a  -> return (Just a)
-                        Nothing -> do put saved -- 状態を復歸
-                                      runParser g
+                        Success a    -> return $ Success a
+                        IllegalInput -> do put saved -- 状態を復歸
+                                           runParser g
+                        ReachedEOF   -> return ReachedEOF
 
 
 oneOf :: [Char] -> Parser Char