debug/0

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(edinburgh)).(can be autoloaded)

Start debugger. In debug mode, Prolog stops at spy and break points, disables last-call optimisation and aggressive destruction of choice points to make debugging information accessible. Implemented by the Prolog flag debug.

Note that the min_free parameter of all stacks is enlarged to 8 K cells if debugging is switched off in order to avoid excessive GC. GC complicates tracing because it renames the _<NNN> variables and replaces unreachable variables with the atom <garbage_collected>. Calling nodebug/0 does not reset the initial free-margin because several parts of the top level and debugger disable debugging of system code regions. See also set_prolog_stack/2.