Add REPL-like printing to %%R cell magic

IPython/extensions/rmagic.py

@@ -182,19 +182,42 b' class RMagics(Magics):'
         self.pyconverter = pyconverter
         self.Rconverter = Rconverter
 
-    def eval(self, line):
+    def eval(self, line, line_mode):
         '''
         Parse and evaluate a line with rpy2.
-        Returns the output to R's stdout() connection
-        and the value of eval(parse(line)).
+        Returns the output to R's stdout() connection, and 
+        the value generated by evaluating the code (see below)
+        
+        In line mode (ie called with %R <stuff>), behavior
+        is unchanged, returns a python object representing
+        the final value, suitable for assignment into a 
+        python variable.
+
+        In cell mode (called with %%R ...), behavior
+        now reproduces the REPL behavior of the R
+        interpreter (which agrees with how cells of
+        python code are handled by the notebook).
+
+        In cell mode if the last line of code is not
+        an assignment, wrapped in invisible(), or 
+        a call to a function which returns its value
+        invisibly, the value will be printed using the
+        show R function.
+
+        Actual evaluation of R code is done via a call
+        of the form withVisible({<code>})
+        
         '''
         old_writeconsole = ri.get_writeconsole()
         ri.set_writeconsole(self.write_console)
         try:
-            value = ri.baseenv['eval'](ri.parse(line))
+            res = ro.r("withVisible({%s})" % line)
+            value = res[0] #value
         except (ri.RRuntimeError, ValueError) as exception:
             warning_or_other_msg = self.flush() # otherwise next return seems to have copy of error
             raise RInterpreterError(line, str_to_unicode(str(exception)), warning_or_other_msg)
+        if not line_mode and ro.conversion.ri2py(res[1])[0]:
+            ro.r.show(value)
         text_output = self.flush()
         ri.set_writeconsole(old_writeconsole)
         return text_output, value
@@ -580,13 +603,13 b' class RMagics(Magics):'
         try:
             if line_mode:
                 for line in code.split(';'):
-                    text_result, result = self.eval(line)
+                    text_result, result = self.eval(line, line_mode)
                     text_output += text_result
                 if text_result:
                     # the last line printed something to the console so we won't return it
                     return_output = False
             else:
-                text_result, result = self.eval(code)
+                text_result, result = self.eval(code, line_mode)
                 text_output += text_result
         
         except RInterpreterError as e: