split Logic.Statement into files, simpler serialization

Logic/Statement/Parse.hs

@@ -0,0 +1,49 @@
+module Logic.Statement.Parse where
+
+import Logic.Parse
+  ( Parser(..)
+  , Input(..)
+  , ParseError
+  , expected
+  , parseToken
+  , parseIf
+  )
+import Logic.Statement (Statement(..))
+
+import Control.Applicative (Alternative((<|>), some))
+import Data.Char (isAlphaNum)
+
+stmtAtom :: Parser Statement
+stmtAtom = Atom <$> parse
+  where
+    parse = some $ parseIf "statement variable" $ \char -> isAlphaNum char || char == '_'
+
+stmtNot :: Parser Statement
+stmtNot = Not <$> (parseToken "!" *> stmt)
+
+stmtBinary :: Parser Statement
+stmtBinary = parseToken "(" *> body <* parseToken ")"
+  where
+    body = (\s1 f s2 -> f s1 s2) <$> stmt <*> parseConnective <*> stmt
+
+    parseConnective =
+      fmap (const And) (parseToken "&")
+      <|> fmap (const Or) (parseToken "|")
+      <|> fmap (const Implies) (parseToken "->")
+      <|> fmap (const Iff) (parseToken "<->")
+      <|> fail
+
+    fail = Parser $ \input -> Left $ expected "connective" input
+
+stmt :: Parser Statement
+stmt = Parser $ \input ->
+  let
+    parser =
+      case inputSeq input of
+        [] -> fail
+        ('!':_) -> stmtNot
+        ('(':_) -> stmtBinary
+        _ -> stmtAtom <|> fail
+  in runParser parser input
+  where
+    fail = Parser $ \input -> Left $ expected "statement" input