laser

# a fake repository

class Repository
  def self.save_calculation(op, n1, n2, result)
    puts "just saved #{op}, #{n1}, #{n2}, #{result}"
  end
end

laser

# implemented in the controller action, result from the 
# calculator operation is passed to the Repository
 
# app/controllers/calculation.rb
def create
  h = ActiveSupport::JSON.decode(request.body)
  
  fx = lambda do |op, mod, repo|
    lambda do |x, y|
      result = mod.method(op.to_sym).to_proc[x, y]

laser

class StatefulCalculator
  def initialize(total)
    @total = total
  end
 
  def add(x)
    StatefulCalculator.new(@total + x)
  end
  
  def sub(x)

laser

require_relative '../foo'

describe StatefulCalculator do
  before(:all) do
    @subject = StatefulCalculator.new
  end

  it 'should add some numbers' do
    expect(@subject.add(5).add(3).add(10).result).to eq(18)
  end

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module Prunable
  def from_assets(assets)
    assets.select &method(:is_prunable?) 
  end
  
  def is_prunable?(asset)
    asset.created_at < Date.today - 30
  end
  
  module_function from_assets, is_prunable?

laser

# lambda is impure: mutates shared state (the fruits hash)
fruits = {}
hashify = lambda do |fruit|
  fruits[fruit] = fruit
end
["apple", "pear"].each &hashify

# lambda is pure: operates only on its arguments
to_nv_pair = lambda do |fruit|
  [fruit, fruit]

laser

class StatefulCalculator
  def initialize
    @total = 0
  end
 
  def add(x)
    @total += x
    self
  end

laser

module StatelessCalculator
  def add(x, y)
    x + y
  end

  def div(num, denom)
    num / denom
  end

  module_function :add, :div

laser

describe StatefulCalculator do
  before(:all) do
    @subject = StatefulCalculator.new
  end
 
  it 'should add some numbers' do
    expect(@subject.add(5).add(3).add(10).result).to eq(18)
  end
end

laser

describe StatefulCalculator do
  before(:all) do
    @subject = StatefulCalculator.new
  end
 
  it 'should add some numbers' do
    expect(@subject.add(5).add(3).add(10).result).to eq(18)
  end
 
  it 'should divide some numbers' do