Why atom([]). is false in SWI prolog software while in GNU prolog is true?

2
votes

When I am using SWI prolog program and run below code the result differs from GNU console as show: atom([]). false in SWI prolog while atom([]). is true in GNU console prolog.

1
prolog

1 Answers

1
votes

SWI-Prolog 7.x and later versions made the empty list its own type, distinct from atom, a deviation from the ISO Prolog Core standard that GNU Prolog follows more closely, including in this case.

P.S. If you want to access a Prolog system (official and de facto) standards conformance, the Logtalk distribution includes a Prolog compliance suite (with ~1700 tests) that you can run with all its supported Prolog systems, which include both SWI-Prolog and GNU Prolog.