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message "A function is a step in a process.  Think back to the last recipe you cooked.  There were steps like 'mix', 'measure', and 'bake'."

goals do
  goal "Create a function"
  goal "Call a function"

step do
  message 'In your text editor, create a new file called area.rb'
  type_in_file 'area.rb', <<-'CONTENTS'
def calculate_circle_area(radius)
  Math::PI * (radius ** 2)

print "What is the radius of your circle? > "
radius = gets.to_i

puts "Your circle has an area of #{calculate_circle_area(radius)}"
  message "Save your work. "

step do
  message "Run the file."
  console 'ruby area.rb'
  message 'When prompted, type in a radius for your circle and hit return.'

step do
  message "We can write functions in IRB too."

  irb <<-IRB
    def backwards(phrase)

 message <<-CONTENTS
A function begins with `def`.  It's followed by the name of the function, and then a list of what you plan to send in.

Inside the function is the code that does the work.  The function ends with a statement that evaluates to a function. What does it mean to evaluate a statement?  When we type `puts "Two plus two is \#{2 + 2}", Ruby evaluates the statement inside the curly brackets.  2 + 2 evaluates to 4, and 3 < 9 evaluates to true.  "Hello".reverse evaluates to "olleH". The function hands the value back by saying it.

After you typed 'end' and hit return, irb typed `nil`.  This is fine. Ruby always reports what it got when it ran your command, and functions result in `nil`.
  message "... and then **call** our function:"

  message "To call a function, first say the name of the function, then send in the values the function needs to do its job."

  irb "backwards 'Hello' "

step do
  message "We can store the result in a variable."
  irb "mirror = backwards 'Hello'"

explanation do
  message "As your programs get more and more complicated, you'll want to group code into **functions** that can be called over and over again."
  message "Pedantic Programmers might want to tell you that Ruby doesn't technically have **functions**, and everything in Ruby is really a **method**. It is appropriate to slap these people."

next_step 'classes'