{"id":8272,"date":"2025-08-17T21:39:56","date_gmt":"2025-08-17T21:39:56","guid":{"rendered":"http:\/\/putridparrot.com\/blog\/?p=8272"},"modified":"2025-08-17T21:39:56","modified_gmt":"2025-08-17T21:39:56","slug":"classes-in-haskell-hint-theyre-more-like-interfaces","status":"publish","type":"post","link":"https:\/\/putridparrot.com\/blog\/classes-in-haskell-hint-theyre-more-like-interfaces\/","title":{"rendered":"Classes in Haskell (hint they’re more like interfaces)"},"content":{"rendered":"

A class (also know as typeclass) in Haskell is more analogous to an interfaces in C# and Java.<\/p>\n

Let’s look at a simple class which will supply a toString function<\/p>\n

\r\nclass ToString a where \r\n  toString :: a -> String\r\n<\/pre>\n
This class allows us to use a toString function on different types. So think of this as an interface where data types that support it will now work with the toString function.<\/p>\n
Let’s just create a simple data type as an example<\/p>\n
\r\ndata Point = Point { x :: Integer, y :: Integer }\r\n<\/pre>\n
Now it’d be cool if we could use code such as print (toString pt)<\/em> and have the output a string like this “X:1, Y:2”. All we need to do is create an instance of the class. Before we do this, we’re going to need to also support converting of an Integer (as it’s used in the Point) to a string, so we may as well create an instance of the ToString class for Integer’s first and then use this code in our Point instance<\/p>\n
\r\ninstance ToString Integer where    \r\n    toString i = show i\r\n<\/pre>\n
So now we’ve got a ToString to handle Integer’s we can combine to create an instance for a Point, like this<\/p>\n
\r\ninstance ToString Point where    \r\n    toString pt = "X:" ++ toString (x pt) ++ ", " ++ "Y:" ++ toString (y pt)\r\n<\/pre>\n","protected":false},"excerpt":{"rendered":"
A class (also know as typeclass) in Haskell is more analogous to an interfaces in C# and Java. Let’s look at a simple class which will supply a toString function class ToString a where toString :: a -> String This class allows us to use a toString function on different types. So think of this […]<\/p>\n","protected":false},"author":1,"featured_media":0,"comment_status":"closed","ping_status":"open","sticky":false,"template":"","format":"standard","meta":{"_jetpack_memberships_contains_paid_content":false,"footnotes":""},"categories":[295],"tags":[],"class_list":["post-8272","post","type-post","status-publish","format-standard","hentry","category-haskell"],"jetpack_sharing_enabled":true,"jetpack_featured_media_url":"","_links":{"self":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/8272","targetHints":{"allow":["GET"]}}],"collection":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts"}],"about":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/types\/post"}],"author":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/users\/1"}],"replies":[{"embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/comments?post=8272"}],"version-history":[{"count":1,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/8272\/revisions"}],"predecessor-version":[{"id":8273,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/posts\/8272\/revisions\/8273"}],"wp:attachment":[{"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/media?parent=8272"}],"wp:term":[{"taxonomy":"category","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/categories?post=8272"},{"taxonomy":"post_tag","embeddable":true,"href":"https:\/\/putridparrot.com\/blog\/wp-json\/wp\/v2\/tags?post=8272"}],"curies":[{"name":"wp","href":"https:\/\/api.w.org\/{rel}","templated":true}]}}