module Fun2Type 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) | Unit | Bool Bool
           | Str String | Char Char | Pair Value 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 (Bool b) = showParen (p>8) (showString "Bool " . shows b);
  showsPrec p (Str d)  = showParen (p>8)
                         (showString "Str " . showChar '"' . showString d. showChar '"');
  showsPrec p (Char c) = showParen (p>8) (showChar '\'' . showChar c . showChar '\'');
  showsPrec p (Fun f)  = showParen (p>8) (showString "Fun <function>");
  showsPrec p (Pair v1 v2) = showParen (p>8) (showChar '(' . showsPrec 0 v1 .
                                              showString ", " . showsPrec 0 v2 .
                                              showChar ')');
  showsPrec p Unit     = showString "Unit"
};

showValue (Num d)   = show d;
showValue (Bool b)  = show b;
showValue (Str str) = str;
showValue (Char c)  = [c];
showValue (Fun _)   = "<function>";
showValue (Pair v1 v2) = "("++show v1++", "++show v2++")";
showValue Unit      = "";

-- Exprの抽象構文
type Decl = (String, Expr);

-- AddとMultの特別扱いをやめる
data Expr = Const Value | Let Decl Expr | Var String  
          | Lambda String Expr | App Expr Expr | If Expr Expr Expr 
            deriving Show; 
}