diff --git a/scripting.py b/scripting.py
index 28ba2f7..ea6421b 100644
--- a/scripting.py
+++ b/scripting.py
@@ -381,7 +381,7 @@ class SyntBinOp(SyntDesc):
                 try:
                     vm.Push(dgEval(left, right))
                 except Exception as e:
-                    Fail.Push(vm, "Failed to " + op + ": " + e, self)
+                    Fail.Push(vm, "Failed to " + op + ": " + str(e), self)
             def Compile(self):
                 return [self.left, self.right, self.Eval]
             clsNew = type(stName, (cls,), {"Compile": Compile, "Eval": Eval, "op": op})
@@ -437,6 +437,16 @@ class SyntSet(SyntDesc):
         if not isinstance(val, Fail):
             vm.Log(vm.vars.Set(self.lvalue.syntVar, vm.Pop(), self))
 
+#debug
+@RegStmt
+class SyntPrint(SyntDesc):
+    desc = [["Print"], " ", (SyntExpr, 1)]
+    expr = SyntDesc.DefProp(0)
+    def Compile(self):
+        return [self.expr, self.Eval]
+    def Eval(self, vm):
+        print vm.Pop()
+
 class Fail(TPrs):
     """
     Failure object.  Our scripting language has no exceptions; instead, if a failure object is involved in a calculation, 
@@ -448,12 +458,12 @@ class Fail(TPrs):
         self.stFailure = stFailure
         self.synt = synt
     @staticmethod
-    def Push(cls, vm, stFailure, synt):
+    def Push(vm, stFailure, synt):
         fail = Fail(stFailure, synt)
         vm.Push(fail)
         vm.Log(fail)
     @staticmethod
-    def Log(cls, vm, stFailure, synt):
+    def Log(vm, stFailure, synt):
         vm.Log(Fail(stFailure, synt))
 
 # projection cursor
@@ -871,6 +881,9 @@ class Pov(TokenClient):
     def run(self):
         while True:
             key = self.client.evKey.receive(self)
+            if key == ansi.K_PGDN:
+                Vm().RunSynt(self.block)
+                continue
             psel = self.pselstate.PselByClient(self.client)
             pwSel = psel.PwSelected(self.PwProjected())
             while pwSel != None:
diff --git a/vm.py b/vm.py
index cb2faa6..7c7c03b 100644
--- a/vm.py
+++ b/vm.py
@@ -1,5 +1,5 @@
 from tpers import *
-from scripting import Fail, Synt
+from scripting import Fail
 
 class Vars(TPrs):
     def InitPersistent(self):
@@ -55,7 +55,7 @@ class Vm(TPrs):
         if len(rNew) == 0: # no-op optimization
             return (r, ip)
         if ip < len(r): # tail call optimization
-            self.rstack.append(r, ip)
+            self.rstack.append((r, ip))
         return (rNew, 0)
         
     def RunSynt(self, synt):
@@ -65,15 +65,15 @@ class Vm(TPrs):
             if ip < len(r):
                 instr = r[ip]
                 ip += 1
-                if isinstance(instr, Synt):
+                if hasattr(instr, "Compile"):
                     (r, ip) = self.CallI(instr, r, ip)
                 elif callable(instr):
                     synt = instr(self)
                     if synt != None:
                         (r, ip) = self.CallI(instr, r, ip)
                 else:
-                    assert False, "invalid opcode"
+                    assert False, "invalid instr " + str(instr)
             else:
-                if len(rstack) == 0:
+                if len(self.rstack) == 0:
                     break
                 (r, ip) = self.rstack.pop()