>>> def makeAdder(x):
   	def inc(y):
   		return y+x
   	return inc
   
   >>> f = makeAdder(3)
   >>> f(4)
   7

So far, so good.

   >>> def makeAdder2(x):
   	v = x
   	def inc(y):
   		v += y
   		return v
   	return inc
   
   >>> f2 = makeAdder2(3)
   >>> f2(4)
   
   Traceback (most recent call last):
     File "<pyshell#15>", line 1, in <module>
       f2(4)
     File "<pyshell#13>", line 4, in inc
       v += y
   UnboundLocalError: local variable 'v' referenced before assignment
   >>>

It looks like you can't mutate variables in a closure. Am I doing it wrong? If you really can't, that seriously limits their power.

--

In Lua:

  > function adder(x)
      local v = x
      function inc(y)
          v = v + y
          return v
          end
      return inc
      end
  >> >> >> >> >> >> >> > f = adder(3)
  > =f(4)
  7
  > =f(4)
  11
  > =f(4)
  15
  >

Works fine. (Also, the syntax is really clean.)