Many thanks for taking the time to explain this, I can see that you have a point.
>Or you can focus on the meaning of the words, then you need just a few types, see how those meanings compound, and go from there.
>I agree, FP is bad at extending things... but it is not FP fault that you see the world as things that need to be extended.
I should probably give another look to FP and continue to study the subject, I have likely been approaching it with a OOP mindset as you suggest. One last question though, what about code duplication ? If you focus on the meaning of words and compounding these meanings to create new things, wouldn't it most of the time create lot of duplicate code ? For example in the case of the local shop and the supermarket, wouldn't you have two functions (or a switch case) containing exactly the same code to calculate the quantity multiplied by the price of the groceries ? One would take a local shop as parameter, and the other one would take a supermarket.
Splitting the sale processing function in two parts - one summing up the groceries and the other one calculating the taxes - so that you can reuse the first function implies knowing in advance the existence of the supermarket structure (which you will only know many years after putting your product in production). Not doing it in advance either means duplicate code or refactoring every time you add an operation. The extension mindset initially comes from the need to avoid code duplication which is known to make maintenance difficult.
Now maybe the strongly-typed experience of FP and its compile-time checks are so convenient in practice that they make the maintenance of this kind of code easily manageable ? Maybe it's not even really duplicate code since what would be a basic number in OOP would be two different types here in FP ? Or maybe it's still thinking about FP from an OOP perspective ?
>Or you can focus on the meaning of the words, then you need just a few types, see how those meanings compound, and go from there.
>I agree, FP is bad at extending things... but it is not FP fault that you see the world as things that need to be extended.
I should probably give another look to FP and continue to study the subject, I have likely been approaching it with a OOP mindset as you suggest. One last question though, what about code duplication ? If you focus on the meaning of words and compounding these meanings to create new things, wouldn't it most of the time create lot of duplicate code ? For example in the case of the local shop and the supermarket, wouldn't you have two functions (or a switch case) containing exactly the same code to calculate the quantity multiplied by the price of the groceries ? One would take a local shop as parameter, and the other one would take a supermarket.
Splitting the sale processing function in two parts - one summing up the groceries and the other one calculating the taxes - so that you can reuse the first function implies knowing in advance the existence of the supermarket structure (which you will only know many years after putting your product in production). Not doing it in advance either means duplicate code or refactoring every time you add an operation. The extension mindset initially comes from the need to avoid code duplication which is known to make maintenance difficult.
Now maybe the strongly-typed experience of FP and its compile-time checks are so convenient in practice that they make the maintenance of this kind of code easily manageable ? Maybe it's not even really duplicate code since what would be a basic number in OOP would be two different types here in FP ? Or maybe it's still thinking about FP from an OOP perspective ?