generalize parser symbols; parser monad

Logic/Statement/Parse.hs

@@ -13,19 +13,23 @@ import Logic.Statement (Statement(..))
 import Control.Applicative (Alternative((<|>), some))
 import Data.Char (isAlphaNum)
 
-stmtAtom :: Parser Statement
+stmtAtom :: Parser Char Statement
 stmtAtom = Atom <$> parse
   where
-    parse = some $ parseIf "statement variable" $ \char -> isAlphaNum char || char == '_'
+    parse = some $ parseIf "variable name" $ \char -> isAlphaNum char || char == '_'
 
-stmtNot :: Parser Statement
+stmtNot :: Parser Char Statement
 stmtNot = Not <$> (parseToken "!" *> stmt)
 
-stmtBinary :: Parser Statement
-stmtBinary = parseToken "(" *> body <* parseToken ")"
+stmtBinary :: Parser Char Statement
+stmtBinary = do
+  parseToken "("
+  s1 <- stmt
+  constructor <- parseConnective
+  s2 <- stmt
+  parseToken ")"
+  return $ constructor s1 s2
   where
-    body = (\s1 f s2 -> f s1 s2) <$> stmt <*> parseConnective <*> stmt
-
     parseConnective =
       fmap (const And) (parseToken "&")
       <|> fmap (const Or) (parseToken "|")
@@ -35,7 +39,7 @@ stmtBinary = parseToken "(" *> body <* parseToken ")"
 
     fail = Parser $ \input -> Left $ expected "connective" input
 
-stmt :: Parser Statement
+stmt :: Parser Char Statement
 stmt = Parser $ \input ->
   let
     parser =