Pangram checker

# title: Pangram checker
# source: https://rosettacode.org/wiki/Pangram_checker
# category: Rosetta Code
# difficulty: Intro
# summary: Check whether a sentence contains every letter of the alphabet at least once.
# tags: popular, strings, analysis
# vibe: 0.2

def is_pangram(sentence)
  alphabet = "abcdefghijklmnopqrstuvwxyz"
  lower = sentence.downcase
  i = 0

  while i < alphabet.length
    letter = alphabet.slice(i)
    if lower.index(letter) == nil
      return false
    end
    i = i + 1
  end

  true
end

def missing_letters(sentence)
  alphabet = "abcdefghijklmnopqrstuvwxyz"
  lower = sentence.downcase
  missing = []
  i = 0

  while i < alphabet.length
    letter = alphabet.slice(i)
    if lower.index(letter) == nil
      missing = missing.push(letter)
    end
    i = i + 1
  end

  missing
end

def run
  fox = "The quick brown fox jumps over the lazy dog"
  almost = "The quick brown fox jumped over the lazy dog"
  {
    fox_pangram: is_pangram(fox),
    almost_pangram: is_pangram(almost),
    almost_missing: missing_letters(almost)
  }
end