SWI-Prolog -- spy/1

Documentation
- Reference manual
  - Built-in Predicates
    - Debugging and Tracing Programs
      - trace/0
      - tracing/0
      - notrace/0
      - notrace/1
      - debug/0
      - nodebug/0
      - debugging/0
      - spy/1
      - nospy/1
      - nospyall/0
      - leash/1
      - visible/1
      - unknown/2
      - style_check/1
- Packages

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

spy(+Pred)

Put a spy point on all predicates meeting the predicate specification Pred. See section A.23.

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

[det]spy(:Spec)

[det]nospy(:Spec)

[det]nospyall

Set/clear spy-points. A successfully set or cleared spy-point is reported using print_message/2, level informational, with one of the following terms, where Spec is of the form M:Head.

spy(Spec)
nospy(Spec)

See also: spy/1 and nospy/1 call the hook prolog:debug_control_hook/1 to allow for alternative specifications of the thing to debug.