Merge pull request #65 from sgraf812/master

Added Alternative constraint and made some minor changes

002_parsers.md

@@ -105,14 +105,14 @@ itself if there is not at least a single match.
 
 ```haskell
 -- | One or more.
-some :: f a -> f [a]
+some :: Alternative f => f a -> f [a]
 some v = some_v
   where
     many_v = some_v <|> pure []
     some_v = (:) <$> v <*> many_v
 
 -- | Zero or more.
-many :: f a -> f [a]
+many :: Alternative f => f a -> f [a]
 many v = many_v
   where
     many_v = some_v <|> pure []

chapter3/parsec.hs

@@ -12,7 +12,7 @@ runParser :: Parser a -> String -> a
 runParser m s =
   case parse m s of
     [(res, [])] -> res
-    [(_, rs)]   -> error "Parser did not consume entire stream."
+    [(_, _)]   -> error "Parser did not consume entire stream."
     _           -> error "Parser error."
 
 item :: Parser Char
@@ -62,7 +62,7 @@ satisfy :: (Char -> Bool) -> Parser Char
 satisfy p = item `bind` \c ->
   if p c
   then unit c
-  else (Parser (\cs -> []))
+  else failure
 
 -------------------------------------------------------------------------------
 -- Combinators