[Pyparsing] Indefinitely recursive grammar because of unary operation in operatorPrecedence()

[Gustavo N. <me...@gu...>]

Hello, everyone.

I'm using the operatorPrecedence() function to define a grammar for boolean 
expressions and this grammar becomes indefinitely recursive when I add an 
unary operation (the negation).

I'm using it like this:
    operation = operatorPrecedence(
        operand,
        [
            (relationals, 2, opAssoc.LEFT),
            (belongs_to, 2, opAssoc.LEFT),
            (is_subset, 2, opAssoc.LEFT),
            (not_, 1, opAssoc.RIGHT),
            (and_, 2, opAssoc.LEFT),
            (ex_or, 2, opAssoc.LEFT),
            (in_or, 2, opAssoc.LEFT),
        ]
    )

Because I want to support operations such as:
 * "pi == 3.1416" (relationals)
 * "3.1416 > pi" (relationals)
 * "user in allowed_people" (belongs_to)
 * "not user in allowed_people" (not_, belongs_to)
 * "not today_is_sunday" (not_)
 * "weather:today_will_rain() and weather:current_season == 'summer'"

This is, I really want relational and set-specific operations (belongs_to, 
is_subset) to have a higher precedence than the negation.

If I remove the not_ operator, the grammar is not indefinitely recursive 
anymore.

What am I doing wrong? I've extracted the relevant code from my project and 
I've attached it to this email, so you can reproduce it easily.

Thanks in advance!
-- 
Gustavo Narea <xri://=Gustavo>.
| Tech blog: =Gustavo/(+blog)/tech  ~  About me: =Gustavo/about |