prologiso-prologlogical-purity

'if' in prolog?

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.

Solution

  • A standard prolog predicate will do this. 

       isfive(5).

    will evaluate to true if you call it with 5 and fail(return false) if you run it with anything else. For not equal you use \=

    isNotEqual(A,B):- A\=B.

    Technically it is does not unify, but it is similar to not equal.

    Learn Prolog Now is a good website for learning prolog.

    Edit: To add another example.

    isEqual(A,A).