174 def _optimize(x):

   175     if x is None:

   176         return 0, x

   177 

   178     op = x[0]

   179     if op in {'string', 'symbol'}:

   180         return 0.5, x

   181     if op == 'kindpat':

   182         w, t = _optimize(x[2])

   183         return w, (op, x[1], t)

   184     if op == 'not':

   185         w, t = _optimize(x[1])

   186         return w, (op, t)

   187     if op in {'and', 'minus'}:

   188         wa, ta = _optimize(x[1])

   189         wb, tb = _optimize(x[2])

   190         return max(wa, wb), (op, ta, tb)

   191     if op == 'or':

   192         ws, ts = zip(*(_optimize(y) for y in x[1:]))

   193         return max(ws), (op,) + ts

   194     if op == 'list':

   195         ws, ts = zip(*(_optimize(y) for y in x[1:]))

   196         return sum(ws), (op,) + ts

   197     if op == 'func':

   198         f = getsymbol(x[1])

   199         w = getattr(symbols.get(f), '_weight', 1)

   200         wa, ta = _optimize(x[2])

   201         return w + wa, (op, x[1], ta)

   202     raise error.ProgrammingError('invalid operator %r' % op)

   203 

   204 def optimize(x):

   205     """Reorder/rewrite evaluatable tree for optimization

   206 

   207     All pseudo operations should be transformed beforehand.

   208     """

   209     _w, t = _optimize(x)

   210     return t

   211