---
title: Drill 10 Solution
tags: Drills-F20, 2020
---

# Drill 10 Solution

## Question 1

For this and the next several questions, we'll use a position datatype
defined as follows:

data Posn:
  | posn(x :: Number, y :: Number)
end

Write an expression that constructs a position with an x-value of 2 and a y-value of 29.

::: spoiler Answer

`posn(2,29)`

To create a data value of type `Posn`, use the `posn` constructor that takes in 2 numbers for its x and y values.

:::

## Question 2

Assume we've defined the `Posn` data-type, as above, and we've defined a `Posn` named `p`.

Write an expression that evaluates to the x-value of `p`.

::: spoiler Answer

`p.x`

Use the `.` operator in order to access the values of a given data construct.

:::

## Question 3

<!-- Question 3 -->
Assume we've defined the `Posn` data-type, as above, and we've defined a `Posn` named `p`.

Write an expression that constructs a new position with each coordinate of `p` doubled.

::: spoiler Answer

`posn(2 * p.x, 2 * p.y)`

We use the posn constructor, passing in 2 * the x and y coordinates of p.

:::

## Question 4

<!-- Question 4 -->
Given this data type Student and value with name `jeff`:

data Student:
  | student(id :: String, major :: String, GPA :: Number)
end

jeff = student("B00", "CS", 3.5)

Which expression creates a new value, `jeff-updated`, with a GPA of 4.0?

( ) jeff-updated = jeff.GPA + .05
( ) jeff-updated = Student(jeff.id, jeff.major, 4.0)
( ) jeff-updated = student(jeff.id, jeff.major, 4.0)
( ) jeff-updated = jeff.GPA.4.0

:::spoiler Answer

( ) jeff-updated = jeff.GPA + .05
( ) jeff-updated = Student(jeff.id, jeff.major, 4.0)
(X) jeff-updated = student(jeff.id, jeff.major, 4.0)
( ) jeff-updated = jeff.GPA.4.0

Use the student constructor in order to make a new value of type Student.

:::

## Question 5

<!-- Question 5 -->
Fill in the blanks to create the data-type `Three-D-Posn` with coordinates x, y, and z.

[Blank1] Three-D-Posn:
   | posn3d(x :: Number, y :: Number, [Blank2])
[Blank3]

:::spoiler Answer

Blank1: `data`

The definition of any datatype begins with the keyword `data`.

Blank2: `z :: Number`

We need the third coordinate `z`, and like the others, it is of type `Number`.

Blank3: `end`

Datatype definitions need to end with `end`, just like a function or `if` expression.

:::