Is there a way to filter a list of union types in Elm without explict case/pattern matching?

Question

I've got a list of things and I want to filter based on a Union type. simplified, it might be something like this:

type Groceries =
  Apples
  | Cheese
  | Widgets

shoppingList = [Apples, Cheese, Cheese, Widgets, Apples]

is there a nice syntax for filtering all the elements that match a particular subtype?

# idk, eg
fruit = shoppingList |> List.filter =Apple? 

我知道我可以使用带有语句的 lambda case，但它看起来太冗长了！

Answer 1

你可以做：

fruit = shoppingList |> List.filter ((==) Apples)

(==)采用中缀等于运算符并将其视为普通函数。然后，应用Apples到它会返回一个部分应用的函数，该函数将应用到它的任何内容与 进行比较Apples。

然而，这仅适用于可以直接比较的简单变体。