make Value objects picklable by rebuilding the memoryview on a new by…

…tearray.

note that this breaks the link of any stored view to the original variable when unpickling.
remove stored view from FOR-stack.
(fix issue #30)

pcbasic/basic/interpreter.py

@@ -382,8 +382,7 @@ def for_(self, args):
         # initialise loop variable
         self._scalars.set(varname, start)
         # obtain a view of the loop variable
-        counter_view = self._scalars.view(varname)
-        self.for_stack.append((varname, counter_view, stop, step, step.sign(), forpos, nextpos,))
+        self.for_stack.append((varname, stop, step, step.sign(), forpos, nextpos,))
         # empty loop: jump to NEXT without executing block
         if (start.gt(stop) if step.sign() > 0 else stop.gt(start)):
             ins.seek(nextpos)
@@ -427,7 +426,7 @@ def iterate_loop(self, varname=None):
         # find the matching NEXT record
         num = len(self.for_stack)
         for depth in range(num):
-            varname2, counter_view, stop, step, sgn, forpos, nextpos = self.for_stack[-depth-1]
+            varname2, stop, step, sgn, forpos, nextpos = self.for_stack[-depth-1]
             if pos == nextpos:
                 if varname is not None and varname2 != self._memory.complete_name(varname):
                     # check once more for matches
@@ -439,6 +438,7 @@ def iterate_loop(self, varname=None):
         else:
             raise error.RunError(error.NEXT_WITHOUT_FOR)
         # increment counter
+        counter_view = self._scalars.view(varname2)
         counter_view.iadd(step)
         # check condition
         loop_ends = counter_view.gt(stop) if sgn > 0 else stop.gt(counter_view)

pcbasic/basic/values/numbers.py

@@ -62,6 +62,17 @@ def __str__(self):
 
     __repr__ = __str__
 
+
+    def __getstate__(self):
+        # can't pickle memoryview
+        self._buffer = bytearray(self._buffer)
+        return self.__dict__
+
+    def __setstate__(self, pickle_dict):
+        # can't pickle memoryview
+        self.__dict__ = pickle_dict
+        self._buffer = memoryview(self._buffer)
+
     def to_value(self):
         """Convert to Python value."""