Sum Type Exercises

module Tutorial.DataTypes.Exercises2

import Tutorial.DataTypes.SumTypes

The solutions to these exercises can be found in src/Solutions/DataTypes.idr.

Exercise 1

Implement an equality test for Title (you can use the equality operator (==) for comparing two Strings):

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eqTitle : Title -> Title -> Bool

Exercise 2

Implement a simple test for Title to check whether or not a custom title is being used:

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isOther : Title -> Bool

Exercise 3

Given our simple Credentials type, there are three ways for authentication to fail:

• An unknown username was used.
• The password given does not match the one associated with the username.
• An invalid key was used.

Encapsulate these three possibilities in a sum type called LoginError. Make sure not to disclose any confidential information, an invalid username should be stored in the corresponding error value, but an invalid password or key should not.

Exercise 4

Implement the following function , which can be used to display an error message to the user after they unsuccessfully tried to login into our web application:

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showError : LoginError -> String