Those prefix operators, in this context, represent instantiation modes, i.e. they tell you which arguments should be variables or instantiated when calling the predicate. They also tell you if an argument will be (possibly further) instantiated by the call. They can also be used to tell you that an argument is going to be meta-interpreted … Read more
Yes, there is such a control construct in ISO Prolog, called ->. You use it like this: ( condition -> then_clause ; else_clause ) Here is an example that uses a chain of else-if-clauses: ( X < 0 -> writeln(‘X is negative. That’s weird! Failing now.’), fail ; X =:= 0 -> writeln(‘X is zero.’) … Read more
tl;dr: No and no. Let’s start with sort/2 which ideally would need n ld(n) comparisons. Fine, but how long does one comparison take? Let’s try this out: tails(Es0, [Es0|Ess]) :- Es0 = [_|Es], tails(Es, Ess). tails([],[[]]). call_time(G,T) :- statistics(runtime,[T0|_]), G, statistics(runtime,[T1|_]), T is T1 – T0. | ?- between(12,15,I), N is 2^I, length(L,N),maplist(=(a),L), tails(L,LT), call_time(sort(LT,LTs), … Read more
The testing for types needs to distinguish itself from the traditional “type testing” built-ins that implicitly also test for a sufficient instantiation. So we effectively test only for sufficiently instantiated terms (si). And if they are not sufficiently instantiated, an appropriate error is issued. For a type nn, there is thus a type testing predicate … Read more
Single quoted items are always atoms. The meaning of double quotes depends on the Prolog flag double_quotes: atom — with this value “a” = a. Nowadays, this is rarely used. But you will find Prolog books where [“abc.pl”] is written. codes — a list of character codes. This is frequently the default, but it leads … Read more