bugfix: stack traces; first class iterators almost working

todo.txt

@@ -1,8 +1,8 @@
 version 0.9.2
 =============
 
-- implement the effect system
-- implement for loop transformation for first class iterators
+- test&finish first class iterators
+- fix closure bug finally
 - overloading based on ASTs: 'constraint' should not be in PType but for the
   parameter *symbol*
 
@@ -11,8 +11,9 @@ version 0.9.2
   - ``hoist`` pragma for loop hoisting: can be easily done with 
     AST overloading + global
 
-- implement the compiler as a service
+- improve the compiler as a service
 - ``=`` should be overloadable; requires specialization for ``=``
+- implement constructors and non-nil types
 - make 'bind' default for templates and introduce 'mixin'; 
   special rule for ``[]=``
 - implicit deref for parameter matching; overloading based on 'var T'
@@ -45,6 +46,7 @@ version 0.9.XX
     echo a
     echo b)
 
+- implement read/write tracking in the effect system
 - implement the "snoopResult" pragma; no, make a strutils with string append
   semantics instead ...
 - implement "closure tuple consists of a single 'ref'" optimization