编程代写 module AST where

module AST where

import Interface

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data Datum
=Number Integer
|Boolean Bool
|Symbol String
|Cons Datum Datum
deriving (Show)

instance SchemeData Datum where
symbol= Symbol
number=Number
boolean=Boolean
proper []=Nil
proper (d:ds)= Cons d (proper ds)

improper [] d=d
improper (d’:ds) d= Cons d’ (improper ds d)

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