lab09: impl pretty print

lab09/jsonParser.hs

@@ -1,5 +1,6 @@
 import Text.ParserCombinators.Parsec
 import System.Environment
+import Data.List (intercalate)
 
 data JValue = JString String
             | JNumber Double
@@ -83,11 +84,33 @@ jsonMember = do
 parseJSON :: String -> Either ParseError JValue
 parseJSON input = parse jsonFile "(unknown)" input
 
+prettyPrint :: JValue -> String
+prettyPrint json = prettyPrint' json 0
+
+prettyPrint' :: JValue -> Int -> String
+prettyPrint' json indent = replicate indent ' ' ++ case json of
+  JString s -> show s
+  JNumber n -> show n
+  JBool b -> show b
+  JNull -> "null"
+  JArray arr -> "[\n"
+                ++  intercalate ",\n" (map (\x -> prettyPrint' x (indent + 2)) arr)
+                ++ "\n]"
+  JObject members -> "{\n"
+                     ++ intercalate ",\n" (map (
+                        \(k, v) -> replicate (indent + 2) ' '
+                        ++ k
+                        ++ ": "
+                        ++ prettyPrint' v 0) members)
+                     ++ "\n"
+                     ++ replicate indent ' '
+                     ++ "}"
+
 main = do
   args <- getArgs
   p <- parseFromFile jsonFile (head args)
   case p of
     Left err  -> print err
-    Right json -> print json
+    Right json -> putStrLn (prettyPrint json)