SWI-Prolog -- create_prolog

Documentation
- Reference manual
  - Overview
    - Environment Control (Prolog flags)
- Packages

Availability:built-in

[YAP]create_prolog_flag(+Key, +Value, +Options)

Create a new Prolog flag. The ISO standard does not foresee creation of new flags, but many libraries introduce new flags. Options is a list of the options below. See also user_flags.

access(+Access): Define access rights for the flag. Values are read_write and read_only. The default is read_write.
type(+Atom): Define a type restriction. Possible values are boolean, atom, oneof(ListOfAtoms), integer, float and term. The default is determined from the initial value. Note that term restricts the term to be ground.
keep(+Boolean): If true, do not modify the flag if it already exists. Otherwise (default), this predicate behaves as set_prolog_flag/2 if the flag already exists.
If the flag has a value, but this value is incompatible with the specified type, a warning is printed and the flag gets the value and type specified by this call to create_prolog_flag/3.