Re: Segfault on X = [a,X].

[Daniel Diaz]

This is not a bug.

X = [a,X] creates a cyclic term during the unification (this happens when a variables is unified with a compound term which contains this variable as subterm). Gnu Prolog does not handle cyclic terms. The standard unification does not perform the occurs check for efficiency reasons. There is a a predicate doing this test: unify_with_occurs_check.

unify_with_occurs_check(X, [a,X]) will fail.

Daniel

Le 23 mars 2012 à 15:24, Konstantin Weitz a écrit :

gprolog segfaults on X = [a,X].

• The type of machine you are using (use uname -a under Unix).
  Linux open-client 3.0.0-16-generic-pae #29-Ubuntu SMP Tue Feb 14 13:56:31 UTC 2012 i686 i686 i386 GNU/Linux
  
  
• GNU Prolog version (use gprolog --version).
  Prolog top-Level (GNU Prolog) 1.4.1
  By Daniel Diaz
  Copyright (C) 1999-2012 Daniel Diaz
  
  
• The precise commands we need to type to reproduce the bug.
  address@hidden:~/gprolog-1.4.1/src/TopComp$ ./gprolog
  GNU Prolog 1.4.1
  By Daniel Diaz
  Copyright (C) 1999-2012 Daniel Diaz
  | ?- X = [a,X].
  Segmentation fault
  
  

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