{-
  Expr: Util の抽象構文木 (goto あり)
 -}

module Expr where

import Data.Char

import Target

-- Expr
type Decl = (String, Expr)
type Decls = [Decl]

-- goto 文を可能にするため、begin 〜 end のなかに変数束縛は許さない
data Expr = Const Target | Var String
          | Let [Decl] Expr | Val Decl Expr 
          | LetGlobal [Decl] Expr | LetLocal [Decl] Expr 
          | Delay Expr
          | Lambda String Expr | App Expr Expr | If Expr Expr Expr
          | While Expr Expr | Begin [LabeledExpr]
          | Break | Continue | Goto String
            deriving Show

type LabeledExpr = (Maybe String, Expr)

isMutVar (h:_) = let c = ord h
                   in 945 <= c && c <= 969 {- 'α' .. 'ω' -}
isMutVar _     = False

-- isLhs (Var x) | isMutVar x = True
-- isLhs _                    = False