intercept/4

Documentation
- Reference manual
  - The SWI-Prolog library
    - library(intercept): Intercept and signal interface
- Packages

Availability::- use_module(library(intercept)).(can be autoloaded)

intercept(:Goal, ?Ball, :Handler, +Arg)

Similar to intercept/3, but the copy of Handler is called as call(Copy,Arg), which allows passing large context arguments or arguments subject to unification or destructive assignment. For example:

?- intercept(send_signal(x), X, Y=X).
true.

?- intercept(send_signal(x), X, =(X), Y).
Y = x.