Add LispVal data type which can hold any Lisp value

LispVal is an algebraic type which is able to hold any of the types
given.

Not sure what the type of `DottedList` is meant to be.

diff --git a/app/Main.hs b/app/Main.hs
index 852089135df8fa8b9ccef54f9699d95bc41d8df2..c64fd18d83b0cdf0575889388df8cfa6344619c8 100644 (file)
--- a/app/Main.hs
+++ b/app/Main.hs
@@ -2,6 +2,13 @@ module Main where
 import Text.ParserCombinators.Parsec hiding (spaces)
 import System.Environment
 
+data LispVal = Atom String
+             | List [LispVal]
+             | DottedList [LispVal] LispVal
+             | Number Integer
+             | String String
+             | Bool Bool
+
 symbol :: Parser Char
 symbol = oneOf "!#$%&|*+-/:<=>?@^_~"