Write a function that takes a string argument and returns True if it is a palindrome and False otherwise (an exercise from Chapter 6 of Think Python by Allen Downey).

Solution in Python

def first(word):
    return word[0]

def last(word):
    return word[-1]

def middle(word):
    return word[1:-1]

def is_palindrome(word):
    if len(word) <=1:
        return True
    if first(word) != last(word):
        return False
    return is_palindrome(middle(word))

words = ['cat', 'noon', 'radar', 'swallows', 'racecar']

for word in words:
  print '%s: %s' % (word, is_palindrome(word))

Solution in Ruby

def first_letter(word)
  word[0]
end

def last_letter(word)
  word[-1]
end

def middle(word)
  word.byteslice(1..-2)
end

def is_palindrome?(word)
  if word.length <= 1
    return 'True'
  elsif first_letter(word) != last_letter(word)
    return 'False'
  else
    return is_palindrome?(middle(word))
  end
end

puts "Palindrome Detector"

array = %w[cat noon radar swallows racecar]
array.each do |word|
  puts "#{word}: #{is_palindrome?(word)}"
end

Outputs:

Palindrome Detector
cat: False
noon: True
radar: True
swallows: False
racecar: True