Add REPL-like printing of final/return value to %%R cell magic

IPython/extensions/rmagic.py

@@ -182,19 +182,42 @@ def __init__(self, shell, Rconverter=Rconverter,
         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>), resulting
+        values are not printed (explicit calls to the 
+        show/print R functions still result in properly
+        captured R output).
+
+        In cell mode (called with %%R ...), behavior
+        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 an R
+        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
@@ -413,13 +436,14 @@ def R(self, line, cell=None, local_ns=None):
             In [9]: %R X=c(1,4,5,7); sd(X); mean(X)
             Out[9]: array([ 4.25])
 
-        As a cell, this will run a block of R code, without bringing anything back by default::
+        As a cell, this will run a block of R code. By default the resulting value
+        is printed if it would be when evaluating the same code within an R REPL.
+        Nothing is returned to python by default.
 
             In [10]: %%R
                ....: Y = c(2,4,3,9)
-               ....: print(summary(lm(Y~X)))
-               ....:
-
+               ....: summary(lm(Y~X))
+
             Call:
             lm(formula = Y ~ X)
 
@@ -580,13 +604,13 @@ def R(self, line, cell=None, local_ns=None):
         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: