> In short, "Here are my gripes about Prolog, a language that I don't understand."

> this article has the flavor of an impatient newbie getting frustrated because he can't be bothered to read the documentation.

The author has written about Prolog in a positive light before (and linked to it in the post), I don't get the impression that these are all "the author doesn't understand what they're doing".

Their first complaint, that "strings are not standardised, so code working with strings in SWI-Prolog is not compatible with Scryer Prolog", seems an appropriate thing to be unhappy about (unless the author is just wrong?).

Your response to their gripe about \+ being "not provable" instead of "negation" notes it's a subtle difference, and that Prolog differs from pure logic there.

The author even notes that doing due diligence, they found a solution to a complaint they had. This doesn't strike me as "can't be bothered to read the documentation".

▲ YeGoblynQueenne 4 hours ago | parent [-]

>> Code logic is expressed entirely in rules, predicates which return true or false for certain values.

Open any Prolog programming textbook (Clocksin & Mellish, Bratko, Sterling & Shapiro, O'Keefe, anything) and the first thing you learn about Prolog is that "code logic" is expressed in facts and rules, and that Prolog predicates don't "return" anything.

The confusion only deepens after that. There are no boolean values? In an untyped language? Imagine that. true/0 and false/0 are not values? In a language where everything is a predicate? Imagine that. Complete lack of understanding that "=" is a unification operator, and that unification is not assignment, like, really, it's not, it's not just a fancy way to pretend you don't do assignment while sneaking it in by the backdoor to be all smug and laugh at the noobs who aren't in the in-group, it's unification, it doesn't work as you think it should work if you think it should work like assignment because everything is immutable so you really, really don't need assignment. Complete misunderstanding of the cut, and its real dangers, complete misunderstanding of Negation as Failure, a central concept in logic programming (including in ASP) and so on and so on and so on and on.

The author failed to do due diligence. And if they've written "in a positive light" about Prolog, I would prefer not to read it because I'll pull my remaining hair out, which is not much after reading this.

▲ dwattttt 4 hours ago | parent [-]

Is it your contention that the author doesn't understand that that Prolog predicates don't "return" anything, that they were expecting assignment rather than unification? I would read it again, their examples clearly state these (noting that the author does say "return", but also clearly shows bidirectional examples).

Both you and GP have had some fairly strong responses to what looked like mild complaints, the kind I would expect anyone to have with a language they've used enough to find edges to.

▲ YeGoblynQueenne 4 hours ago | parent [-]

See this:

  The original example in the last section was this:

  foo(A, B) :-
      \+ (A = B),
      A = 1,
      B = 2.

  foo(1, 2) returns true, so you'd expect f(A, B) to return A=1, B=2. But it returns false.

foo(A,B) fails because \+(A = B) fails, because A = B succeeds. That's because = is not an assignment but a unification, and in the query foo(A,B), A and B are variables, so they always unify.

In fact here I'm not sure whether the author expects = to work as an assignment or an equality. In \+(A = B) they seem to expect it to work as an equality, but in A = 1, B = 2, they seem to expect it to work as an assignment. It is neither.

I appreciate unification is confusing and takes effort to get one's head around, but note that the author is selling a book titled LOGIC FOR PROGR∀MMERS (in small caps) so they should really try to understand what the damn heck this logic programming stuff is all about. The book is $30.

	▲	dwattttt 4 hours ago \| parent [-]
		The author also wrote in the same article: > This is also why you can't just write A = B+1: that unifies A with the compound term +(B, 1)