[Pyparsing] operatorPrecedence: Problems with Power and Unary Minus

[Eike W. <eik...@gm...>]

The parser generated by the function "operatorPrecedence" can not 
correctly parse the power operator in conjunction with the unary 
minus operator. 

The Python reference says:
"The power operator binds more tightly than unary operators on its 
left; it binds less tightly than unary operators on its right."
[http://docs.python.org/ref/power.html]
I think this can't be done with operatorPrecedence. 

Is there a more elegant (shorter) way to get the correct syntax than 
what I did in this example program here?
    http://pastebin.com/f7eb6be8a

Maybe a parser that gets this right could be added to 
operatorPrecedence. The syntax could look like this for example:
expression = operatorPrecedence( u_expr,
  [OpPower(power='**', sign=oneOf('+ -')),
   (oneOf('* /'),   2, opAssoc.LEFT),
   (oneOf('+ -'),   2, opAssoc.LEFT),
  ])

I think an example like the little program I've posted here, should be 
included in the examples, so that newbies get mathematical 
expressions right. For me mathematical expressions are by far the 
most tricky part in writing the parser for my toy language.

Kind regards,
Eike