Edit Question - KnowledgeHub

Title Body

Suppose I am defining a Haskell function f (either pure or an action) and somewhere within f I call function g. For example: f = ... g someParms ... How do I replace function g with a mock version for unit testing? If I were working in Java, g would be a method on class SomeServiceImpl that implements interface SomeService . Then, I'd use dependency injection to tell f to either use SomeServiceImpl or MockSomeServiceImpl . I'm not sure how to do this in Haskell. Is the best way to do it to introduce a type class SomeService: class SomeService a where g :: a -> typeOfSomeParms -> gReturnType data SomeServiceImpl = SomeServiceImpl data MockSomeServiceImpl = MockSomeServiceImpl instance SomeService SomeServiceImpl where g _ someParms = ... -- real implementation of g instance SomeService MockSomeServiceImpl where g _ someParms = ... -- mock implementation of g Then, redefine f as follows: f someService ... = ... g someService someParms ... It seems like this would work, but I'm just learning Haskell and wondering if this is the best way to do this? More generally, I like the idea of dependency injection not just for mocking, but also to make code more customizable and reusable. Generally, I like the idea of not being locked into a single implementation for any of the services that a piece of code uses. Would it be considered a good idea to use the above trick extensively in code to get the benefits of dependency injection? EDIT: Let's take this one step further. Suppose I have a series of functions a, b, c, d, e, and f in a module that all need to be able to reference functions g, h, i, and j from a different module. And suppose I want to be able to mock functions g, h, i, and j. I could clearly pass the 4 fu

Tags (comma-separated) Cancel