🚀 go-pugleaf

>	op(Prec, Type, Rator)
> 
> cannot be used in the mode
> 
>       op(OUTPUT, OUTPUT, INPUT),
> 
> to find the precedence and fixity of an operator, but only in the mode
> 
>       op(INPUT, INPUT, INPUT).


The predicate that you need is current_op/3.  This can be called
with any or all of its arguments unbound.

There is a reasonably well-accepted rule that predicates
which cause side-effects, like op/3, should be kept separate
from predicates which merely inspect the state of the system,
like current_op/3.  A benefit of this rule is that if you
accidentally call a predicate like op/3 with an unbound variable
as an argument, you should get an error, rather than having
the goal either fail quietly or fill in some value and continue.