module TPDB.Data.Rule where

import TPDB.Data.Identifier
import Data.Typeable

data Relation = Strict |  Weak | Equal deriving ( Eq, Ord, Typeable, Show )

data Rule a = Rule
  { lhs :: a, rhs :: a 
  , relation :: Relation
  , top :: Bool
  -- TPDC (XTC) represents SRS as TRS,
  -- e.g.,  "ab -> ba" is "a(b(x)) -> b(a(x))",
  -- and when we convert back (as we need for CPF),
  -- need to use the original variable in the rule
  , original_variable :: Maybe Identifier 
  }
    deriving ( Eq, Ord, Typeable )

strict :: Rule a -> Bool
strict u = case relation u of Strict -> True ; _ -> False

weak :: Rule a -> Bool
weak u = case relation u of Weak -> True ; _ -> False

equal :: Rule a -> Bool
equal u = case relation u of Equal -> True ; _ -> False

instance Functor Rule where 
    fmap f u = u { lhs = f $ lhs u, rhs = f $ rhs u }