Ruby proc composition example

proc_comp.rb

TAX_RATE = 0.4
BENEFIT_COST = 1000

SALARY_IN_PENCE = 15_000 * 100

subtract_benefit = ->(salary) { salary - BENEFIT_COST }
pay_tax = ->(salary) { salary * (1 - TAX_RATE) }

calculate_take_home_pay = subtract_benefit >> pay_tax
puts "Pre-tax benefit: #{calculate_take_home_pay.call(SALARY_IN_PENCE)}"

sad_calculate_take_home_pay = pay_tax >> subtract_benefit

puts "After-tax benefit: #{sad_calculate_take_home_pay.call(SALARY_IN_PENCE)}"

format_salary = ->(salary) { "£#{format('%0.2f', salary / 100.0)}" }

pretty_take_home_pay = calculate_take_home_pay >> format_salary

puts "Pretty: #{pretty_take_home_pay.call(SALARY_IN_PENCE)}"