Day 18 - Structured data

Introduction to Structured Data

1. Introduction (10 minutes)

• Overview:

  • Explain that many pieces of real‑world information consist of several parts that should be kept together.
  • Introduce the idea of structured data—data that bundles multiple fields (attributes) into a single value.

• Example Context:

  • A library system where each book has a title, an author, and a page count.

• Learning Goals:

  • Understand what structured data is.
  • Learn how to define a new structured type in Pyret.
  • Create and annotate instances of structured data.
  • Write functions to extract fields from structured data.

• Do Now:

  • Ask: “What kinds of information in your daily life are made up of several parts? (e.g., a contact entry, a recipe, a product listing)”
  • Briefly share examples with the class.

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2. Defining and Creating Structured Data (20 minutes)

• Defining a Structured Data Type:

  • Introduce a new data type called BookRecord to represent a book.
  • Pyret Code:

    # Define a structured type for a book with three fields: title, author, and pages
    data BookRecord:
      | book(title :: String, author :: String, pages :: Number)
    end

• Creating Examples:

  • Create instances of BookRecord using the constructor book.
  • Examples:

    # Create some book records
    the-dispossessed = book("The Dispossessed", "Ursula K. Le Guin", 387)
    to-the-lighthouse = book("To the Lighthouse", "Virginia Woolf", 209)
    brave-new-world = book("Brave New World", "Aldous Huxley", 268)

• Annotations for Structured Data:

  • Emphasize that field annotations (e.g., title :: String) help catch type errors.

• Interactive Exercise:

  • Ask: “What do you expect to happen if you try to create a book with a non-number for pages?”
  • Discuss potential type errors and the role of annotations.

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3. Programming with Structured Data (20 minutes)

• Extracting Fields:

  • Write a function that returns a summary string for a book.
  • Example Function:

    fun book-summary(b :: BookRecord) -> String:
      # We can access fields using dot notation (e.g., b.title)
      b.title + " by " + b.author + " (" + string-from-number(b.pages) + " pages)"
    end

• Interactive Exercise:

  • Ask: “What is the result of book-summary(the-disposessed)?”
  • Expected output: "The Disposesssed by Ursula K. Le Guin (387 pages)".

• Additional Exercise:

  • Write a function is-long-book that returns true if a book has more than 350 pages.
  • Example Implementation (guided by class discussion):

    fun is-long-book(b :: BookRecord) -> Boolean:
      b.pages > 350
    end
  • Test with the-disposessed and brave-new-world.

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4. Wrap-Up (10 minutes)

• Recap Key Points:
  • Structured data groups multiple fields together.
  • We define structured types using data and create instances by calling the constructor.
  • Fields are accessed with the dot notation.