Re: uncaught exception: error(existence_error(procedure, p/1), top_level/0)

[Adam Russell]

In order to define new predicates in the top  level you need to furst consult the pseudo-file user to specify the terminal. Press ctrl-D when finished.  http://www.gprolog.org/manual/html_node/gprolog007.html

For example, you can see that I can reproduce your error, but then fix things. Note that the ctrl-D entered before the "user compiled..." line is not visible, but that is what exits the pseudo-file and causes what has been typed to be compiled.

$ gprolog

GNU Prolog 1.4.5 (32 bits)

Compiled Dec  3 2020, 00:37:14 with gcc

By Daniel Diaz

Copyright (C) 1999-2020 Daniel Diaz

| ?- p(a).

uncaught exception: error(existence_error(procedure,p/1),top_level/0)

| ?- [user].

compiling user for byte code...

p(a).

user compiled, 1 lines read - 168 bytes written, 20696 ms

(4 ms) yes

| ?- p(X).

X = a

yes

| ?-

This is great for learning, but more typically you would enter your predicates in a file and then consult that file in the top-level, or specify it on the gprolog command line, or even just compile it with gplc.

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From: Users-prolog on behalf of William Clodius via Users list for the GNU implementation of Prolog
Sent: Monday, May 3, 2021 6:58 PM
To: users-prolog@gnu.org
Subject: uncaught exception: error(existence_error(procedure, p/1), top_level/0)

I am trying to teach myself prolog starting with the J. R. Fisher tutorial https://www.cpp.edu/~jrfisher/www/prolog_tutorial/pt_framer.html. I worked through the first few exercises using gprolog with no problems. I exited prolog for a break, but now when I restarted it I find myself unable to define procedures and am getting an uncaught exception:

gprolog
GNU Prolog 1.4.5 (64 bits)
Compiled Jul 14 2018, 16:25:15 with /usr/bin/clang
By Daniel Diaz
Copyright (C) 1999-2018 Daniel Diaz
| ?- p(a).
uncaught exception: error(existence_error(procedure,p/1),top_level/0)

I suspect I exited prolog improperly and there is an invalid state somewhere in a cache. FWIW I am running on a MacBook with OS X Big Sur version 11.3. Are there any suggestions about how to fix this?