Learn to Program Ch 14 - Blocks and Procs

LtP_14_procs

# Extracting multiples of 3
multiples_of_3 = Proc.new do |n|
  n % 3 == 0
end

(1..100).to_a.select(&multiples_of_3)

# Round down method
floats = [1.2, 3.45, 0.91, 7.727, 11.42, 482.911]
round_down = Proc.new { |n| n.floor }

ints = floats.collect(&round_down)

# EXAMPLE 1 ------------------------------------
# toast = Proc.new do
#   puts "Cheers!"
# end

# toast.call
# toast.call
# toast.call

# EXAMPLE 2 ------------------------------------
# do_you_like = Proc.new do |good_stuff|
#   puts "I *really* like #{good_stuff}!"
# end

# do_you_like.call 'chocolate'
# do_you_like.call 'figs'

# EXAMPLE 3 ------------------------------------
# def do_self_importantly some_proc
#   puts "Everybody just HOLD ON! I'm doing something..."
#   some_proc.call
#   puts "OK everyone, I'm done. As you were."
# end

# say_hello = Proc.new do
#   puts "hello"
# end

# say_goodbye = Proc.new do
#   puts "goodbye"
# end

# do_self_importantly say_hello
# do_self_importantly say_goodbye

# EXAMPLE 4 ------------------------------------
# def maybe_do some_proc
#   if rand(2) == 0
#     some_proc.call
#   end
# end

# def twice_do some_proc
#   some_proc.call
#   some_proc.call
# end

# wink = Proc.new do 
#   puts "<wink>"
# end

# glance = Proc.new do
#   puts "<glance>"
# end

# maybe_do wink
# maybe_do wink
# maybe_do glance
# maybe_do glance
# twice_do wink
# twice_do glance

# EXAMPLE 5 ------------------------------------
# def do_until_false first_input, some_proc
#   input = first_input
#   output = first_input
#   while output
#     input = output
#     output = some_proc.call input
#   end
#   input
# end

# build_array_of_squares = Proc.new do |array|
#   last_number = array.last
#   if last_number <= 0
#     false
#   else
#     # Take off the last number...
#     array.pop
#     # ...and replace it with its square...
#     array.push last_number*last_number
#     # ...followed by the next smaller number.
#     array.push last_number-1
#   end
# end

# always_false = Proc.new do |just_ignore_me|
#   false
# end

# puts do_until_false([5], build_array_of_squares).inspect

# yum = 'lemonade with a hint of orange blossom water'
# puts do_until_false(yum, always_false)

# EXAMPLE 6 ------------------------------------
# def compose proc1, proc2
#   Proc.new do |x|
#     proc2.call(proc1.call(x))
#   end
# end

# square_it = Proc.new do |x|
#   x * x
# end

# double_it = Proc.new do |x|
#   x + x
# end

# double_then_square = compose double_it, square_it
# square_then_double = compose square_it, double_it

# puts double_then_square.call(5)
# puts square_then_double.call(5)