Product and Sum types

Presentation based on the post "Why Sum Types Matter in Haskell" https://medium.com/@willkurt/why-sum-types-matter-in-haskell-ba2c1ab4e372

Transcript

1. Sum types in Haskell @filippovitale × @mwotton
3. struct author_name { char *first_name; char *last_name; }; struct book { author_name author; char *isbn; char *title; int year_published; double price; };
4. data AuthorName = AuthorName {firstName :: String ,lastName :: String } data Book = Book {author :: AuthorName ,isbn :: String ,title :: String ,year :: Int ,price :: Double }
5. // The curse of product types: Hierarchical design public class StoreItem { String title; int yearPublished; double price; } public class Book extends StoreItem { Author author; String isbn; } public class VinylRecord extends StoreItem { String artist; }
6. Sum types: Combining Types with ‘or’
7. data Name = Name FirstName LastName | NameWithMiddle FirstName MiddleName LastName | TwoInitialsWithLast Char Char LastName | FirstNameWithTwoInits FirstName Char Char public class Name { String firstName; String lastName; String middleName; char firstInitial; char middleInitial; char lastInitial; }
8. data Book = Book {author :: Creator , isbn :: String , bookTitle :: String , bookYear :: Int , bookPrice :: Double} data VinylRecord = VinylRecord { artist :: Creator , recordTitle :: String , recordYear :: Int , recordPrice :: Double} data StoreItem = BookItem Book | RecordItem VinylRecord
9. data CollectibleToy = CollectibleToy { name :: String , descrption :: String , toyPrice :: Double} data StoreItem = BookItem Book | RecordItem VinylRecord | ToyItem CollectibleToy
10. price :: StoreItem -> Double price (BookItem book) = bookPrice book price (RecordItem record) = recordPrice record price (ToyItem toy) = toyPrice toy https://medium.com/@willkurt/why-sum-types-matter-in-haskell-ba2c1ab4e372