{- Starter program for Assignment 8, CSE 341, Winter 2003
   simplifying set expressions in Haskell
   This is the same as starter.hs, except that it uses a fancier test
   function.  (The test function is more versatile, but uses concepts we
   won't cover in class, specifically I/O monads.)
-}

union :: Eq a => [a] -> [a] -> [a]
-- write your union function here
-- the type says that it takes a list of a's, which must be a type
-- that supports equality tests
--
-- the following definition of union is wrong -- it's just to get Haskell
-- to accept this program
union x y = []


-- also write declarations and definitions for intersect and difference


-- here is a partial definition of the SetExpr data type
-- you just need to add elements for Intersect and Difference
data SetExpr = Set [Integer] 
               | Var String 
               | Union SetExpr SetExpr
               deriving (Eq,Show,Read)


-- here is the type declaration for set_simplify, and an (incorrect)
-- definition (all this version does is simplify an expression to itself)
set_simplify :: SetExpr -> SetExpr
set_simplify s = s



{- tests is a list of SetExpr to use in testing set_simplify.  It should
   consist of pairs of expressions: an original, and the expected result 
   of the simplification.  
   you should add additional tests to the list -}
tests :: [SetExpr]
tests = [ 
  Set [1,3], Set [1,3],
  (Union (Var "x") (Var "x")),  (Var "x"),
  (Union (Var "x") (Var "y")),  (Union (Var "x") (Var "y"))
 ]


{- runtests is a function to run all the tests in a list of pairs 
   of SetExpr.  
   runtests uses monads, which allows easy input/output.
   (We will probably not get to monads in 341; in that case, just use 
   this code without worrying about how it works.) 
-}

runtests [] = do return (True)

runtests ( orig : expected : tests )  
  = do putStr "Original: "
       putStrLn (show orig)
       putStr "Expected result: "
       putStrLn (show expected)
       let actual = set_simplify orig
       putStr "Actual result: "
       putStrLn (show actual)
       let passed = (expected==actual)
       putStr "Passed? "
       putStrLn (show passed)
       putStrLn ""
       otherresults <- runtests tests
       return (passed && otherresults)


-- function to run all the tests in 'tests'.  
-- Use this to test your program
run 
  = do r <- runtests tests
       putStr "Passed all tests? "
       putStrLn (show r)