module AST where

import Data.List


data Program = Program [Value]

type Name = String

data Value
    = VList [Value]
    | VNum Int
    | VString String
    | VName Name
    | VQuoted Value
    | VLambda [Name] Value
    | VBuiltin String
    | VEllipsis
  deriving (Eq)


instance Show Program where
    show (Program l) = intercalate "\n" $ map show l

instance Show Value where
    show (VList es) = '(' : intercalate " " (map show es) ++ ")"
    show (VNum i) = show i
    show (VString s) = show s
    show (VName n) = n
    show (VQuoted e) = '\'' : show e
    show (VLambda as v) = "(lambda (" ++ intercalate " " as ++ ") " ++ show v ++ ")"
    show (VBuiltin str) = "[[builtin " ++ str ++ "]]"
    show VEllipsis = "..."


fromVName :: Value -> Maybe Name
fromVName (VName s) = Just s
fromVName _ = Nothing

fromVNum :: Value -> Maybe Int
fromVNum (VNum i) = Just i
fromVNum _ = Nothing

fromVString :: Value -> Maybe String
fromVString (VString s) = Just s
fromVString _ = Nothing