'How to check if a number is even?
I have a predicate that checks for even. However, when I perform querying, it always returns false. I'm new to prolog, and I'm really puzzled by this behavior
Even(N):- N mod 2 = 0.
Update:
If I change it to Even(N):- 0 is N mod 2., then it works. Why is this the case?
Solution 1:[1]
You are not using the proper operators and have some typos! First, the name of the predicate starts with a small letter (even instead of Even). Operator for the equality comparison is =:= (you are using = that is for unification! and is to apply a value to a variable. Although what you right means 0 is 0 for the even numbers and works here but in some situation will be failed. See here to know more about this.).
even(N):- mod(N,2) =:= 0.
Solution 2:[2]
= is for unification and =:= nd is are considered equals to in Prolog. It's as simple as that. Also, whether it's a rule or fact, it always starts so that the code will be:
even(N):-
mod(N,2) =:= 0.
Sources
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Source: Stack Overflow
| Solution | Source |
|---|---|
| Solution 1 | |
| Solution 2 | Jeremy Caney |