andrea kao 高沁蘭

Prime.prime?

2015-12-31

I solved this Codewars kata tonight, yay:

require 'prime'

def prime_bef_aft(num)
  primes = []
  Prime.each(num){ |n| primes << n }
  primes.last == num ? bef_prime = primes[-2] : bef_prime = primes.last
  aft_prime = Prime.first(primes.size + 1).last
  [bef_prime, aft_prime]
end

I need to examine the top-rated solution, though:

require 'prime'

def bef_prime(num)
  num -= 1
  return num.prime? ? num : bef_prime(num)
end

def aft_prime(num)
  num += 1
  return num.prime? ? num : aft_prime(num)
end

def prime_bef_aft(num)
  [bef_prime(num), aft_prime(num)]
end

The title of this post is only generally relevant to the topic at hand; I just really like the idea of reading Ruby code as human language. Prime.prime? seems to read as some sort of existential question.