Sum types in Haskell @filippovitale × @mwotton 

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struct author_name { char *first_name; char *last_name; }; struct book { author_name author; char *isbn; char *title; int year_published; double price; }; 

data AuthorName = AuthorName {firstName :: String ,lastName :: String } data Book = Book {author :: AuthorName ,isbn :: String ,title :: String ,year :: Int ,price :: Double } 

// 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; } 

Sum types: Combining Types with ‘or’ 

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; } 

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 

data CollectibleToy = CollectibleToy { name :: String , descrption :: String , toyPrice :: Double} data StoreItem = BookItem Book | RecordItem VinylRecord | ToyItem CollectibleToy 

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