Sticker Shop
10 Points
phantom-types
Instructions
Lucy has an online sticker shop, where she sells cute stickers featuring everyone's favourite programming languages. People from all around the world buy her stickers, and she's having some trouble dealing with all the different currencies.
Create a program that Lucy can use to calculate prices while being sure that she's always using the correct currency.
1. Define the Usd, Eur, and Jpy types
These types are used to represent the different currencies that Lucy's customers use to buy her stickers.
They are to be used as phantom types and do not need to have any constructors.
2. Define the Money type.
The Money type should have an Int field for the amount of money, a currency phantom type parameter, and it should be an opaque type.
3. Define dollar, euro, and yen functions
Define the dollar, euro, and yen functions that take an Int argument and return a Money value with the correct currency.
4. Define the total function
Define the total function which takes a list of Money values and returns the total amount of money in the list.
total([euro(120), euro(200), euro(145)])
// -> euro(465)Sticker Shop
10 Points
phantom-types
Instructions
Lucy has an online sticker shop, where she sells cute stickers featuring everyone's favourite programming languages. People from all around the world buy her stickers, and she's having some trouble dealing with all the different currencies.
Create a program that Lucy can use to calculate prices while being sure that she's always using the correct currency.
1. Define the Usd, Eur, and Jpy types
These types are used to represent the different currencies that Lucy's customers use to buy her stickers.
They are to be used as phantom types and do not need to have any constructors.
2. Define the Money type.
The Money type should have an Int field for the amount of money, a currency phantom type parameter, and it should be an opaque type.
3. Define dollar, euro, and yen functions
Define the dollar, euro, and yen functions that take an Int argument and return a Money value with the correct currency.
4. Define the total function
Define the total function which takes a list of Money values and returns the total amount of money in the list.
total([euro(120), euro(200), euro(145)])
// -> euro(465)