Somewhat working lambdas

Architectural changes to lambda evaluation and parsing to allow
for correct expression evaluation. Contains several failing AI-generated
tests and we're still failing tests for erroring incomplete definitions

src/Main.hs

@@ -11,3 +11,6 @@ import Text.Megaparsec (runParser)
 
 main :: IO ()
 main = repl Map.empty --(Map.fromList [("__result", Leaf)])
+
+runSapling :: String -> String
+runSapling s = show $ result (evalSapling Map.empty $ parseSapling s)