SWI-Prolog -- chr

Documentation
- Reference manual
  - CHR: Constraint Handling Rules
    - Debugging CHR programs
      - CHR Debugging Predicates
        
        chr_trace/0
        
        chr_notrace/0
        
        chr_leash/1
        
        chr_show_store/1
        
        find_chr_constraint/1
- Packages

chr_leash(+Spec)

Define the set of CHR ports on which the CHR tracer asks for user intervention (i.e. stops). Spec is either a list of ports as defined in section 9.4.1 or a predefined‘alias’. Defined aliases are: full to stop at all ports, none or off to never stop, and default to stop at the call, exit, fail, wake and apply ports. See also leash/1.