Lisp のリストを表示する関数

Lisp のリストを表示する関数を作ってみた。

data Symbol = I Integer | S String | Nil | C Cell deriving (Show, Read, Eq)

 

data Cell = Cell { car_ :: Symbol, cdr_ :: Symbol} deriving (Show, Read, Eq)

 

cons a b = C Cell { car_ = a, cdr_ = b }

 

car (C cell) = car_ cell

cdr (C cell) = cdr_ cell

  

listToString ls   = "(" ++ listToString_ ls ++ ")"

listToString_ Nil = ""

listToString_ ls = case (car ls) of

          (C _) -> "(" ++ listToString_ (car ls) ++ ")(" ++ listToString_ (cdr ls)++")"

          (I x) -> (show x) ++ (outSpace ls) ++listToString_ (cdr ls)

          (S x) -> "\""++ x ++ "\"" ++ (outSpace ls) ++listToString_ (cdr ls)

 

outSpace ls = if (cdr ls)==Nil then "" else " "

 

cell = cons (S "World!") Nil

list1 = cons (S "Hello") cell

cell2 = cons (I 456) Nil

list2 = cons (I 123) cell2

list3 = cons list1 list2

 

main = do

  putStrLn $ listToString cell

  putStrLn $ listToString list1

  putStrLn $ listToString list2

  putStrLn $ listToString list3 

 *Main> cell

 C (Cell {car_ = S "World!", cdr_ = Nil})

 *Main> putStrLn $ listToString cell

 ("World!")

 *Main> list1

 C (Cell {car_ = S "Hello", cdr_ = C (Cell {car_ = S "World!", cdr_ = Nil})})

 *Main> putStrLn $ listToString list1

 ("Hello" "World!")

 *Main> list2

 C (Cell {car_ = I 123, cdr_ = C (Cell {car_ = I 456, cdr_ = Nil})})

 *Main> putStrLn $ listToString list2

 (123 456)

 *Main> list3

 C (Cell {car_ = C (Cell {car_ = S "Hello", cdr_ = C (Cell {car_ = S "World!", cdr_ = Nil})}),

          cdr_ = C (Cell  {car_ = I 123, cdr_ = C (Cell {car_ = I 456, cdr_ = Nil})})})

 *Main> putStrLn $ listToString list3

 ( ("Hello" "World!") (123 456))