Menu
Is there a way to do an if in prolog, e.g. if a variable is 0, then to do some actions (write text to the terminal). An else isn't even needed, but I can't find any documentation of if.
321
Prolog has a builtin if-then-else syntax.
Program. % If-Then-Else statement gt(X,Y) :- X >= Y,write('X is greater or equal'). gt(X,Y) :- X < Y,write('X is smaller'). % If-Elif-Else statement gte(X,Y) :- X > Y,write('X is greater').
=:= expression is meaning of exactly equal. such as in JavaScript you can use === to also see if the type of the variables are same. Basically it's same logic but =:= is used in functional languages as Prolog, Erlang.
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.') ; writeln('X is positive.') ) Note that if you omit the else-clause, the condition failing will mean that the whole if-statement will fail. Therefore, I recommend always including the else-clause (even if it is just true).
92
If you love us? You can donate to us via Paypal or buy me a coffee so we can maintain and grow! Thank you!
Donate Us With
