JPL: Equivalence Predicate `toString` Method Generates Quotation Marks

Discussion
1

Hi. The following code using JPL creates compound which tests equivalence of two arguments:

Compound compound = new Compound("\\==", new Term[]{new Atom("c"), new Atom("d")});

After that, when toString() method is called on that compound, it yields '\=='(a, b), which shows two quotation marks around predicate \== .
According to JPL documentation, the toString() method returns:

a prefix functional representation of a Compound of the form name(arg1,…), where ‘name’ is quoted iff necessary (to be valid Prolog source text) and each argument is represented according to its toString() method. Lists are represented depending on JPL.LIST_TOSTRING_TEXTUAL

However, when I use the string else where, I have to manually remove those quotation marks. For example:

Compound compound = new Compound("\\==", new Term[]{new Atom("c"), new Atom("d")});
t = Term.textToTerm(compound.toString());

the above code throws an exception:

Exception in thread “main” org.jpl7.PrologException: PrologException: error(syntax_error(undefined_char_escape(‘=’)), string(‘’=='(c, d) . ', 1))

I’m woundering why the quotaiton marks are needed here?

2

They are not. \== should either be written as '\\==' or simply as \==. I do recall there have been some discussions about toString() before. I don’t really recall (I’m not a JPL user) the verdict. Possibly the old issues on the jpl repo at github shine some light.