Played our first session of DW last week, great fun!

We have a question about how to handle weapon reach.  One of our players is using a halberd, which has a range of "reach".  Let's say he's fighting a monster with a range of "close".  Fictionally, he has just closed into range with the halberd.  How should we be handling combat at this point? 

• Does he just do damage, and the monster can't ever close into close range?  (barring something else happening fictionally, like getting surrounded)
• Do we use hack and slash, but on a 9- the monster's move is "move into sword range"?
• Something else?
  

Also unsure what is supposed to happen when a monster is "too close" for the range.  Defy danger to withdraw?  Seems like combat will just turn into a series of "I move back", "he moves forward" steps.

Same things appear to apply to close range vs. hand range as well.