Just playing around with some Ruby.

practice.rb

# Eager (non-lazy) sequence generation:
(0..8).each_cons(2).map { |a,b| a + b }

# Another form (of above)
(1..10).each_with_object([1]) { |i,a| a[i] = a[i-1] + 2 }

# Eager Fibonacci (generates n+1 Fibonacci numbers)
(2..10).each_with_object([0,1]) { |i,a| a[i] = a[i-2] + a[i-1] }

# Corrected for n = 1 or 2, and removed extra number
def fib(n)
  (n == 1) ? [0] : (2..(n-1)).each_with_object([0,1]) { |i,a| a[i] = a[i-2] + a[i-1] }
end

# Or like this
def fib(n)
  (n == 1) ? [0] : (2..(n-1)).each_with_object([0,1]) do |i,a|
    a[i] = a[i-2] + a[i-1]
  end
end

def factorial n
  (n == 0) ? 1 : n * factorial(n - 1)
end

(0..10).each do |n|
  puts "#{n}! = #{factorial n}"
end

# Non-recursive definition
def factorial n
  (n == 0) ? 1 : (1..n).reduce(:*)
end

(0..10).each do |n|
  puts "#{n}! = #{factorial n}"
end

# Even simpler factorial
def factorial n
  (1..n).reduce(1, :*)
end

(0..10).each do |n|
  puts "#{n}! = #{factorial n}"
end