Cut(!) and fail inside nested once/1 calls?

[Dave Sworin]

Please advise whether the following behavior is a bug.

Test platforms tried: 1) Ubuntu 10.10 64-bit gprolog 1.3.1 and 2) Mint 13 64-bit gprolog 1.4.1

 

once((

(once(((4 == 5) ; (!,fail)))) ;

(write(a))

)).

 

This query writes the letter a to the standard output.  (I hope I typed all the parentheses correctly!)

 

If I remove the once/1 call inside the outer once/1, the cut(!) and fail works as expected.

 

once((

((((4 == 5) ; (!,fail)))) ;

(write(a))

)).

 

This query fails with a "no".

 

Is the cut(!) and fail scope limited inside the once/1 call?

 

Dave

 

PS: Everything seems to work fine in gprolog 1.4.1 but in the debugger I experienced segmentation

violations debugging after consulting a very large prolog file bug exact same thing works fine in

gprolog 1.3.1.  Have other people experienced this too.  I do not have a small example.