Flags

Prolog options are controlled by the setting of various flags. A changeable flag can be set by using set_prolog_flag/2, and the current value of a flag can be accessed by current_prolog_flag/2. Non-changeable flags serve to furnish information about the implementation. The initial values of the flags depend on whether PrologJ is started up in full, iso, edinburgh, or basic mode, as listed for each flag. PrologJ supports the following flags:
 

• break_fresh_variables - if on, use a fresh set of variables names for each invocation of break/0 or the debugger's break command; if off, use the variable used when reading the term that initiated computation. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: on   edinburgh: on   basic: on
   
  
• char_conversion - enable/disable conversions specified by char_conversion/2. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: on   edinburgh: off   basic: on
   
  
• debug - enable/disable the debugging facilities and Debug predicate set. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: on   basic: on
   
  
• detect_float_overflow_underflow - throw an error if overflow or underflow occurs in float arithmetic. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: on   edinburgh: on   basic: on
   
  
• dialect - specify which builtin predicates to make available. Possible values:
  • iso - those in the ISO dialect.
  • edinburgh - those in the Edinburgh dialect.
  • both - those in both the ISO and Edinburgh dialects.
  Initial values: full: both   iso: iso   edinburgh: edinburgh   basic: both
   
  
• double_quotes - specify how a string enclosed in " is interpreted. Possible values:
  • chars - a list of one-character atoms.
  • codes - a list of integer codes.
  • atom - an atom.
  Initial values: full: codes   iso: codes   edinburgh: codes   basic: codes
   
  
• enforce_directives - enforce the use of the discontiguous, dynamic, multifile, and public directives. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: on   edinburgh: off   basic: off
   
  
• ensure_loaded - specify which version of a module to load if both source and compiled versions are available, if the ensure_loaded directive appears in a source file being consulted by consult/1 or reconsult/1 or it is entered interactively. (When this directive appears in a file that is being compiled it specifies that a compiled module of that name is to be loaded when the compiled module is itself loaded.) Possible values:
  • newest - load the newest.
  • source_preferred - load the source version.
  • compiled_preferred - load the compiled version.
  Initial values: full: newest   iso: newest   edinburgh: newest   basic: newest
   
  
• function - enable/disable the user-defined functions extension. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• fuzzy - enable/disable the fuzzy logic extension and associated predicates. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• grammar_rules - enable/disable the grammar rules feature and associated predicate. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• java - enable/disable the use of the Java extension and the entry, java, and main directives. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• leash - specify which ports of a leashed predicate are actually leashed. Possible values:
  • - do not leash any ports.
  • c - leash only the call port.
  • e - leash only the exit port.
  • ce - leash only the call and exit ports.
  • r - leash only the redo port.
  • cr - leash only the call and redo ports.
  • er - leash only the exit and redo ports.
  • cer - leash only the call, exit, and redo ports.
  • f - leash only the fail port.
  • cf - leash only the call and fail ports.
  • ef - leash only the exit and fail ports.
  • cef - leash only the call, exit and fail ports.
  • rf - leash only the redo and fail ports.
  • crf - leash only the call, redo, and fail ports.
  • erf - leash only the exit, redo, and fail ports.
  • cerf - leash all ports.
  Initial values: full: cerf   iso: cerf   edinburgh: cerf   basic: cerf
   
  
• miscellaneous - enable/disable the miscellaneous predicates extension. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• operator_single_slash - specify how operator / is interpreted. Possible values:
  • either - integer division if both operands are integers; otherwise real division.
  • real - real division in all cases.
  Initial values: full: either   iso: real   edinburgh: either   basic: either
   
  
• sql - enable/disable the relational database extension. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• set - enable/disable the set processing predicates. Possible values:
  • off - disables the feature.
  • on - enables the feature.
  Initial values: full: on   iso: off   edinburgh: off   basic: off
   
  
• stack_trace - specify what sort of stack trace is printed for an uncaught error. Possible values:
  • standard - print a standard stack trace - prolog history plus Java history of methods that are not part of the PrologJ implementation.
  • none - do not print any stack trace.
  • prolog - print the prolog history only
  • java - print the entire Java history only (including the PrologJ implementation part).
  • all - print the entire Prolog and Java histories (including the PrologJ implementation part).
  Initial values: full: standard   iso: standard   edinburgh: standard   basic: standard
   
  
• unknown - specify what happens when an undefined predicate is called. Possible values:
  • error - throw an error.
  • warning - issue a warning and fail.
  • fail - fail without error or warning.
  Initial values: full: warning   iso: error   edinburgh: fail   basic: fail
   
  
• bounded - specifies that PrologJ supports unbounded integers. Unchangeable.
• max_arity - specifies the maximum permissible arity of a compound term. Unchangeable.
• integer_rounding_function - specifies how floats are rounded to integers by round/1. Unchangeable.
• version - specifies the current version of PrologJ. Unchangeable.