set_prolog_flag

[David]

Are there restrictions in GNU Prolog on using set_prolog_flag?

 

I want to be able to set user definable flags (like I do in SWI prolog, for example). 

For example, the statement :

 

|?- set_prolog_flag('userflag','yes').

 

returns:

 

uncaught exception: error(domain_error(prolog_flag,userflag),set_prolog_flag/2)

 

--Thanks for thoughts on such a simple question.

 

David Bennett