 
   sr4_pool: (dice, edge=0) =>
     dice += edge
-    return ZERO if dice == 0
+    return 0 if dice == 0
     if dice < 0
       throw new DiceError "Cannot roll a negative number of dice."
     hits = 0

class DiceError extends SyntaxError
  constructor: (@message) ->
    @name = "DiceError"

ZERO =
  type: "Number"
  value: 0

class DiceInterpretter
  constructor: (@results = [], @dice_rolled = []) ->

        throw "Bad unary operation: #{op}"

  roll: (dice, sides) =>
    return 0 if dice == 0 or sides == 0
    if dice < 0
      throw new DiceError "Cannot roll a negative number of dice."
    if sides < 0
