Add some notes

TODO.md

@@ -15,6 +15,10 @@ print the generated type variable for every subexpression in an expression
 
 ## Schala-lang syntax
 
+-idea: the `type` declaration should have some kind of GADT-like syntax
+
+-idea: I should make the BNF grammar part of the documentation...
+
 - Idea: if you have a pattern-match where one variant has a variable and the other lacks it
 instead of treating this as a type error, promote the bound variable to an option type