gprolog error for default functions: error(existence_error...

Asked Nov 04 '16 at 15:58

Active Nov 04 '16 at 15:58

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I keep running into an existence error for many different default functions in prolog (I'm using gprolog). For example...

| ?- assert(a(1)).
uncaught exception: error(existence_error(procedure,assert/1),top_level/0)
| ?- g_assign(GVarName, 0).
uncaught exception: error(instantiation_error,g_assign/2)
| ?- b_setval(A, 0).
uncaught exception: error(existence_error(procedure,b_setval/2),top_level/0)

Do I need to install something else?

Essentially, I'm trying to find a way to define a global variable. I thought something like this might be the best way...

fact(List).

predicate(List) :- 
    ...some code...,
    assert(fact(List)).

and then to invoke the "global variable" I would use fact(List).

asked Nov 04 '16 at 15:58

Kendall Weihe

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Read the GNU Prolog manual. GNU Prolog has `asserta/1` and `assertz/1`. You can define `assert(X) :- assertz(X).` if you wish. – lurker Nov 04 '16 at 16:10
very good thank you! – Kendall Weihe Nov 04 '16 at 16:11
any idea why `g_assign ` doesn't exist? – Kendall Weihe Nov 04 '16 at 16:15
1

That's a different error, `instantiation_error`, which means it expects at least one of the variables you provided to be instantiated, but it was not. See http://www.gprolog.org/manual/html_node/gprolog045.html. – lurker Nov 04 '16 at 16:28
1

See [this](http://stackoverflow.com/a/20027252/772868) for `assert`. – false Nov 04 '16 at 19:27

gprolog error for default functions: error(existence_error...

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