fix for mathics#331

mathics/builtin/control.py

@@ -58,8 +58,13 @@ def apply(self, expr, evaluation):
 
         items = expr.get_sequence()
         result = Symbol('Null')
-        for expr in items:
-            result = expr.evaluate(evaluation)
+        for i, expr in enumerate(items):
+            term = expr.evaluate(evaluation)
+            if i == len(items) - 1 and term == Symbol('Null'):
+                # if the last expression is `Null` then return second last expression
+                evaluation.quiet_result = True
+                break
+            result = term
         return result
 
 

mathics/core/evaluation.py

@@ -161,6 +161,7 @@ def __init__(self, definitions=None,
 
         self.quiet_all = False
         self.quiet_messages = set()
+        self.quiet_result = False
         self.format = format
         self.catch_interrupt = catch_interrupt
 
@@ -216,7 +217,7 @@ def evaluate():
                     stored_result = self.get_stored_result(result)
                     self.definitions.add_rule('Out', Rule(
                         Expression('Out', line_no), stored_result))
-                if result != Symbol('Null'):
+                if not self.quiet_result and result != Symbol('Null'):
                     return self.format_output(result)
                 else:
                     return None