diff --git a/IPython/frontend/cocoa/cocoa_frontend.py b/IPython/frontend/cocoa/cocoa_frontend.py
index 5f617e7..cea94d9 100644
--- a/IPython/frontend/cocoa/cocoa_frontend.py
+++ b/IPython/frontend/cocoa/cocoa_frontend.py
@@ -29,6 +29,7 @@ import uuid
 from Foundation import NSObject, NSMutableArray, NSMutableDictionary,\
                         NSLog, NSNotificationCenter, NSMakeRange,\
                         NSLocalizedString, NSIntersectionRange
+                        
 from AppKit import NSApplicationWillTerminateNotification, NSBeep,\
                     NSTextView, NSRulerView, NSVerticalRuler
 
@@ -181,17 +182,26 @@ class IPythonCocoaController(NSObject, FrontEndBase):
             if(self.is_complete(self.currentBlock())):
                 self.execute(self.currentBlock(),
                                 blockID=self.currentBlockID)
-                self.currentBlockID = self.nextBlockID()
+                self.startNewBlock()
+                
                 return True
             
             return False
         
         elif(selector == 'moveUp:'):
-            self.replaceCurrentBlockWithString(textView, self.get_history_item_previous(self.currentBlock()))
+            prevBlock = self.get_history_previous(self.currentBlock())
+            if(prevBlock != None):
+                self.replaceCurrentBlockWithString(textView, prevBlock)
+            else:
+                NSBeep()
             return True
         
         elif(selector == 'moveDown:'):
-            self.replaceCurrentBlockWithString(textView, self.get_history_item_next(self.currentBlock()))
+            nextBlock = self.get_history_next(self.currentBlock())
+            if(nextBlock != None):
+                self.replaceCurrentBlockWithString(textView, nextBlock)
+            else:
+                NSBeep()
             return True
         
         elif(selector == 'moveToBeginningOfParagraph:'):
@@ -265,6 +275,13 @@ class IPythonCocoaController(NSObject, FrontEndBase):
         return (completions,0)
     
     
+    def startNewBlock(self):
+        """"""
+        
+        self.currentBlockID = self.nextBlockID()
+    
+    
+    
     def nextBlockID(self):
         
         return uuid.uuid4()
@@ -312,7 +329,8 @@ class IPythonCocoaController(NSObject, FrontEndBase):
     
         
     def render_error(self, failure):
-        self.insert_text(str(failure))
+        self.insert_text('\n\n'+str(failure)+'\n\n')
+        self.startNewBlock()
         return failure
     
     
@@ -344,6 +362,7 @@ class IPythonCocoaController(NSObject, FrontEndBase):
     def replaceCurrentBlockWithString(self, textView, string):
         textView.replaceCharactersInRange_withString_(self.currentBlockRange(),
                                                         string)
+        self.currentBlockRange().length = len(string)
         r = NSMakeRange(textView.textStorage().length(), 0)
         textView.scrollRangeToVisible_(r)
         textView.setSelectedRange_(r)
diff --git a/IPython/frontend/frontendbase.py b/IPython/frontend/frontendbase.py
index ea8aeb8..12e1dc3 100644
--- a/IPython/frontend/frontendbase.py
+++ b/IPython/frontend/frontendbase.py
@@ -20,16 +20,15 @@ __docformat__ = "restructuredtext en"
 #-------------------------------------------------------------------------------
 import string
 import uuid
+import _ast
 
+import zope.interface as zi
 
 from IPython.kernel.core.history import FrontEndHistory
 from IPython.kernel.core.util import Bunch
-
 from IPython.kernel.engineservice import IEngineCore
 
-import zope.interface as zi
-
-import _ast
+from twisted.python.failure import Failure
 
 ##############################################################################
 # TEMPORARY!!! fake configuration, while we decide whether to use tconfig or
@@ -115,11 +114,11 @@ class IFrontEnd(zi.Interface):
         pass
     
     
-    def get_history_item_previous(currentBlock):
+    def get_history_previous(currentBlock):
         """Returns the block previous in  the history."""
         pass
     
-    def get_history_item_next(currentBlock):
+    def get_history_next(currentBlock):
         """Returns the next block in the history."""
         
         pass
@@ -226,38 +225,52 @@ class FrontEndBase(object):
         Result:
             Deferred result of self.interpreter.execute
         """
-        # if(not isinstance(block, _ast.AST)):
-        #     block = self.compile_ast(block)
+        
+        if(not self.is_complete(block)):
+            return Failure(Exception("Block is not compilable"))
         
         if(blockID == None):
             blockID = uuid.uuid4() #random UUID
         
         d = self.engine.execute(block)
         d.addCallback(self._add_block_id, blockID)
+        d.addCallback(self._add_history, block=block)
         d.addCallback(self.update_cell_prompt)
         d.addCallbacks(self.render_result, errback=self.render_error)
         
         return d
     
+    
     def _add_block_id(self, result, blockID):
-        """add_block_id"""
+        """Add the blockID to result"""
         
         result['blockID'] = blockID
         
         return result
     
+    def _add_history(self, result, block=None):
+        """Add block to the history"""
+        
+        assert(block != None)
+        self.history.add_items([block])
+        self.history_cursor += 1
+        
+        return result
+    
     
-    def get_history_item_previous(self, currentBlock):
+    def get_history_previous(self, currentBlock):
         """ Returns previous history string and decrement history cursor.
         """
+        print self.history
         command = self.history.get_history_item(self.history_cursor - 1)
+        print command
         if command is not None:
             self.history.input_cache[self.history_cursor] = currentBlock
             self.history_cursor -= 1
         return command
     
     
-    def get_history_item_next(self, currentBlock):
+    def get_history_next(self, currentBlock):
         """ Returns next history string and increment history cursor.
         """
         command = self.history.get_history_item(self.history_cursor + 1)