DSL building patterns in Ruby - Mini Project: Build & Apply

Building a Simple DSL in Ruby

📖 Scenario: Imagine you want to create a small language inside Ruby to describe a recipe. This language will let you write recipes in a way that looks like plain English but runs as Ruby code.

🎯 Goal: You will build a simple Domain Specific Language (DSL) in Ruby to describe a recipe with ingredients and steps. You will then print the recipe in a readable format.

📋 What You'll Learn

Create a class called Recipe to hold ingredients and steps

Add a method called ingredient to add ingredients with name and quantity

Add a method called step to add instructions

Use a block to define the recipe content

Print the recipe with ingredients and steps in order

💡 Why This Matters

🌍 Real World

DSLs help make complex tasks easier by creating small languages tailored to specific problems, like writing recipes, configuring apps, or describing workflows.

💼 Career

Understanding DSL building patterns is useful for Ruby developers working on frameworks, testing tools, or configuration systems where readable and flexible code is important.

1

Create the Recipe class with storage

Create a class called Recipe with two instance variables: @ingredients and @steps. Initialize both as empty arrays inside the initialize method.

Ruby

class Recipe
  def initialize
    # Your code here
  end
end

Need a hint?

Use @ingredients = [] and @steps = [] inside the initialize method.

2

Add methods to add ingredients and steps

Add two methods inside the Recipe class: ingredient(name, quantity) which adds a hash with keys :name and :quantity to @ingredients, and step(description) which adds the description string to @steps.

Ruby

class Recipe
  def initialize
    @ingredients = []
    @steps = []
  end

  # Add ingredient method here
  # Add step method here

Need a hint?

Use @ingredients << { name: name, quantity: quantity } and @steps << description inside the methods.

3

Add a class method to build the recipe with a block

Add a class method self.build that takes a block. Inside it, create a new Recipe instance, yield it to the block, and return the instance.

Ruby

class Recipe
  def initialize
    @ingredients = []
    @steps = []
  end

  def ingredient(name, quantity)
    @ingredients << { name: name, quantity: quantity }
  end

  def step(description)
    @steps << description
  end

  # Add self.build method here

Need a hint?

Use yield(recipe) to run the block with the recipe object.

4

Print the recipe ingredients and steps

Add a method print_recipe inside the Recipe class that prints "Ingredients:" followed by each ingredient's quantity and name on separate lines, then prints "Steps:" followed by each step numbered starting from 1. Then create a recipe using Recipe.build with these exact ingredients and steps:
ingredient("Flour", "2 cups"), ingredient("Sugar", "1 cup"), step("Mix ingredients"), step("Bake for 30 minutes"). Finally, call print_recipe on the created recipe.

Ruby

class Recipe
  def initialize
    @ingredients = []
    @steps = []
  end

  def ingredient(name, quantity)
    @ingredients << { name: name, quantity: quantity }
  end

  def step(description)
    @steps << description
  end

  def self.build
    recipe = new
    yield(recipe)
    recipe
  end

  # Add print_recipe method here
end

# Create recipe with Recipe.build and add ingredients and steps
# Call print_recipe on the recipe

Need a hint?

Use puts to print lines. Use each to loop through ingredients and steps. Use each_with_index to number steps.