module FunType where {


-- Monadic Versionのために必要
type M a = a;

unitM :: a -> M a;
unitM a = a;

bindM :: M a -> (a -> M b) -> M b;
m `bindM` k = k m;



data Value = Num Double | Fun (Value -> M Value);

-- Value値を表示するために必要
instance Show Value where {
  showsPrec p (Num d) = showParen (p>8) (showString "Num ". shows d);
  showsPrec p (Fun f) = showParen (p>8) (showString "Fun <function>")
};

showValue (Num d)   = show d;
showValue (Fun _)   = "<function>";

-- Exprの抽象構文
type Decl = (String, Expr);
data Expr = Mult Expr Expr | Add Expr Expr | Const Value
          | Let Decl Expr | Var String  
          | Lambda String Expr | App Expr Expr 
            deriving Show;
}