lab01: impl json

lab01/JSON.hs

@@ -0,0 +1,49 @@
+---SOLUTION
+-- A JSON library written in Haskell, adapted from an example
+-- from "Real World Haskell".
+
+-- Note that the module name must match the name of the file.
+module JSON (
+  JValue(..), --The (..) means that we are exporting the type and all of its constructors
+  toString,
+  isNull,
+  jsonRightTriangles)
+where
+
+data JValue = JString String
+			| JNumber Double
+			| JBool Bool
+			| JNull
+			| JObject [(String, JValue)]
+			| JArray [JValue]
+  deriving (Eq, Ord, Show)
+
+
+--The type annotation indicates that the function takes a JValue and returns a String
+toString :: JValue      -> String
+toString (JString s)    = "\"" ++ s ++ "\""
+toString (JNumber n)    = show n
+toString (JBool True)   = "true"
+toString (JBool False)  = "false"
+toString JNull          = "null"
+toString (JArray lst)   = "[" ++ list2str lst ++ "]"
+toString (JObject obj)  = "{\n" ++ obj2str obj ++ "\n}"
+
+list2str :: [JValue] -> String
+list2str [] = ""
+list2str (x:[]) = (toString x)
+list2str (x:xs) = (toString x) ++ ",\n " ++ (list2str xs)
+
+obj2str :: [(String, JValue)] -> String
+obj2str [] = ""
+obj2str ((k,v):[]) = k ++ ":" ++ toString v
+obj2str ((k,v):xs) = k ++ ":" ++ toString v ++ "," ++ obj2str xs
+
+isNull JNull  = True
+isNull _      = False
+
+jsonRightTriangles = JArray [ JObject [("a",JNumber a), ("b",JNumber b), ("c",JNumber c)] |
+  a<-[1..10],
+  b<-[1..10],
+  c<-[1..10],
+  a^2 + b^2 == c^2]