Prolog Language Operators Operator declaration
Example
In Prolog, custom operators can be defined using op/3:
op(+Precedence, +Type, :Operator)
-
Declares Operator to be an operator of a Type with a Precedence. Operator can also be a list of names in which case all elements of the list are declared to be identical operators.
-
Precedence is an integer between 0 and 1200, where 0 removes the declaration.
-
Type is one of:
xf,yf,xfx,xfy,yfx,fyorfxwherefindicates the position of the functor andxandyindicate the positions of the arguments.ydenotes a term with a precedence lower or equal to the precedence of the functor, whereasxdenotes a strictly lower precedence.- Prefix:
fx,fy - Infix:
xfx(not associative),xfy(right associative),yfx(left associative) - Postfix:
xf,yf
- Prefix:
Example usage:
:- op(900, xf, is_true).
X_0 is_true :-
X_0.
Example query:
?- dif(X, a) is_true.
dif(X, a).
