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Recitation 7 — Structured and conditional data

Skills: 4​

Reading: 6.1, 6.2​

Structured Data​

Many pieces of real-world information consist of several parts that should be kept together. Structured data bundles multiple fields into a single value.

Defining a Structured Data Type​

Define a new data type called Student to represent a student:

data Student:
  | student(name :: String, id :: Number, gpa :: Number)
end

Creating Examples​

Create instances of Student using the constructor student:

alice = student("Alice Smith", 12345, 3.7)
bob = student("Bob Martinez", 23456, 3.2)
carol = student("Carol Johnson", 34567, 3.9)

What do you expect to happen if you try to create a student with a string for the ID number?

Extracting Fields​

Design a function student-info that returns a formatted string for a student:

What is the result of student-info(alice)?

Writing Functions with Structured Data​

Design a function honors-student that returns true if a student has a GPA of 3.5 or higher:

Conditional Data​

Sometimes data can come in multiple forms and we need a way to represent alternatives within one type. Conditional data can be one of several variants.

Defining a Conditional Data Type​

Define a new type called OrderType with three variants:

data OrderType:
  | pickup
  | delivery(address :: String, tip :: Number)
  | curbside(car-color :: String, license-plate :: String)
end

How many different ways can someone receive their order according to our OrderType?

Creating Examples​

Create instances of OrderType:

order-1 = pickup
order-2 = delivery("360 Huntington Ave, Boston MA", 5.00)
order-3 = curbside("red", "ABC123")

Taking Apart Variants with cases​

Design a function order-instructions that returns instructions for fulfilling an order:

fun order-instructions(o :: OrderType) -> String:
  cases (OrderType) o:
    | pickup => # YOUR CODE HERE
    | delivery(addr, tip-amount) => # YOUR CODE HERE
    | curbside(color, plate) => # YOUR CODE HERE
  end
where:
  order-instructions(pickup) is "Order ready for pickup at counter"
  order-instructions(order-3) is "Look for red car with plate ABC123 in parking lot"
end

Processing Fields in Variants​

Design a function total-cost that calculates the total cost including any service fees:

What information do we use and ignore in each case?

Wrap-Up​

When would you use structured data instead of separate variables? Why is pattern matching with cases better than using if-statements for conditional data?