Using insert predicate in SWI-Prolog swish?

Question

I'm trying to execute what seems like a simple three lines of code

insert(X,[],[X]).
insert(X,[H|T],Z):-X>=H,Z=[X,H|T].
insert(X,[H|T],Z):-X<H,insert(X,T,Z2),Z=[H|Z2].

but for some reason I can't get it to compile or execute on the many online code compilers out there SWISH, IDEone, etc. It seems the problem is "insert" isn't a recognized predicate. I tried a few google searches and nothing seems to come up for insert. Thanks! (Sorry very new to Prolog)

ERROR: /home/uJ0Y9U/prog:13:
    No permission to modify static procedure `true/0'
Warning: /home/uJ0Y9U/prog:15:
    Goal (directive) failed: user:main
ERROR: '$runtoplevel'/0: Undefined procedure: program/0
   Exception: (3) program ? EOF: exit

edit: It seems there was an issue with non-ascii characters. That caused an error of ERROR: /home/F3Vzlp/prog:10:21: Syntax error: Operator expected ERROR: /home/F3Vzlp/prog:11:21: Syntax error: Operator expected

score 3 · Answer 1 · answered Aug 27 '15 at 01:58

3

There is a problem with the dash sign you used (‐) which appears not to be the ascii minus sign (-).

In fact, if you type in a terminal:

iconv -c -f utf-8 -t ascii <<EOF

then paste your code and press CTRL+D, you'll see the minus sign will get stripped away..

Try to rewrite your code manually, or paste it somewhere and manually correct the minus sign in :- and you'll be OK.

answered Aug 27 '15 at 01:58

fferri

18,285
5
46
95

However, this doesn't solve the later errors, see updated question. – Aaron_H Aug 27 '15 at 02:06
2

@Aaron_H: Please don't modify your question. This answer is now no longer an answer to your question. – false Aug 27 '15 at 05:25
1

Ok sorry, I re-modified it to be explicit should someone else come along with the same problem. – Aaron_H Aug 28 '15 at 20:47

score 3 · Accepted Answer · answered Aug 27 '15 at 02:54

Your program works e.g. with http://swish.swi-prolog.org/, swipl, and gprolog. Here is a transcript using the latter:

$ gprolog --consult-file insert.prolog
GNU Prolog 1.4.4 (64 bits)
...
insert.prolog compiled, 3 lines read - 1234 bytes written, 16 ms
| ?- insert(1,[0,2,4], X).
insert(1,[0,2,4], X).

X = [1,0,2,4] ? ;
;

no
| ?-

The first error message you encountered (regarding "true/0") suggests that there was some extraneous text somewhere.

By the way, your program can be improved slightly. (Hint: there's no need for Z.)

Using insert predicate in SWI-Prolog swish?

2 Answers2