Haskell Arith

arith.hs

data Expr
    = Const Integer         -- values (integers)
    | Add Expr Expr         -- addition
    | Mul Expr Expr         -- multiplication
    | If Expr Expr Expr Expr -- conditional branching (If a == b then c else d)
    -- Not turing complete, but should be capable of evaluating most functions.
    deriving (Show, Eq)

eval :: Expr -> Integer
eval (Const x) = x
eval (Add a b) = (eval a) + (eval b)
eval (Mul a b) = (eval a) * (eval b)
eval (If a b c d) = eval $ if a == b then c else d

-- parse, etc TBD
parse :: String -> Maybe Expr

data Token 
    = Num Integer 
    | Add | Mul | If
    deriving (Show, Eq)

tokenize :: String -> Maybe [Token]
resolvePrecedence :: [Token] -> Maybe Expr