Grammar.hs

module Grammar where

data Expr a = Plus (Expr a) (Term a)
            | Minus (Expr a) (Term a)
            | ExprTerm (Term a)

data Term a = Mult (Term a) (Factor a)
            | Div (Term a) (Factor a)
            | TermFactor (Factor a)

data Factor a = Constant a
              | FactorExpr (Expr a)


runExpr :: Expr Double -> Double
runExpr (Plus expr term)  = runExpr expr + runTerm term
runExpr (Minus expr term) = runExpr expr - runTerm term
runExpr (ExprTerm term)   = runTerm term


runTerm :: Term Double -> Double
runTerm (Mult term fac)  = runTerm term * runFac fac
runTerm (Div term fac)   = runTerm term / runFac fac
runTerm (TermFactor fac) = runFac fac


runFac :: Factor Double -> Double
runFac (Constant a)      = a
runFac (FactorExpr expr) = runExpr expr