如何在Haskell中定義Lispy數據類型？

Question

我正在爲Coursera的AI Planning課程編程Lispy PDDL解析器。

如何在Haskell中定義Lispy數據類型？

Answer 1

我Lispy PDDL分析器：

https://dl.dropbox.com/u/46434672/Code/LispyPddlParser.hs

的DWR-operators.txt文件：

https://spark-public.s3.amazonaws.com/aiplan/resources/DWR-operators.txt

Answer 2

它看起來像是，不是嗎？

{-# LANGUAGE FlexibleInstances #-} 

import Data.List 

data S s = T s | S [S s] deriving (Eq) 

instance Show (S String) where 
show (T s) = s 
show (S list) = "(" ++ (intercalate " " $ map show list) ++ ")" 

sExpr = S [T "define",T "x",T "10",S [T "print",T "hello"],S []] 

main = do 
putStrLn $ show sExpr 

運行的結果主要：

(define x 10 (print hello)())