As LdBeth points out your isPrime "incorrectly" reports 1 as prime.
Reading your isPrime, your definition of a prime number would be: A number which doesn’t have a factor in the set ]1;number[
As far as I'm aware the most widely used definition of a prime number is: A number that have exactly two positive factors.
If we go by this latter definition of a prime number we can make small changes to your APL code to make it fit: IsPrime←{2=+/0=⍵ |⍨ ⍳⍵}
Your definition of a prime number is of course not unheard of, and it is a good implementation of it :)
Reading your isPrime, your definition of a prime number would be: A number which doesn’t have a factor in the set ]1;number[
As far as I'm aware the most widely used definition of a prime number is: A number that have exactly two positive factors.
If we go by this latter definition of a prime number we can make small changes to your APL code to make it fit: IsPrime←{2=+/0=⍵ |⍨ ⍳⍵}
Your definition of a prime number is of course not unheard of, and it is a good implementation of it :)