whispers in monads
It can be done "functionally" but doesn't necessarily have to be done in an FP paradigm to use this pattern.
There are other strategies to push resource handling to the edges of the program: pools, allocators, etc.
It can be done "functionally" but doesn't necessarily have to be done in an FP paradigm to use this pattern.
There are other strategies to push resource handling to the edges of the program: pools, allocators, etc.
Consider your basic point of sale terminal. They get a payment token from your provider using the chip, but they don't resolve the transaction with your card/chip still inserted. I don't know any monad trick that would let that general flow appear in a static piece of the code?
Can you implement it using functional code? Yes. Just make sure you wind up with partial states. And often times you are best off explicitly not using the RAI pattern for some of these. (I have rarely seen examples where they deal with this. Creating and reconciling transactions often have to be separate pieces of code. And the reconcile code cannot, necessarily, fallback to create a transaction if they get a "not found" fault.)
Yes, the monadic part is the functional core, and the runtime is the imperative shell.
> Consider your basic point of sale terminal. They get a payment token from your provider using the chip, but they don't resolve the transaction with your card/chip still inserted. I don't know any monad trick that would let that general flow appear in a static piece of the code?
What do you mean by Monad trick? That's precisely the kind of thing the IO monad exists for. If you need to fetch things on an API: IO. If you need to read/save things on a DB: IO. DB Transaction: IO.
Granted, in trying to find some examples that stick in my memory, I can't really find any complete examples anymore. Mayhap I'm imagining a bad one? (Very possible.)
If the transaction object is serializable you can just store it in a DB, for example. If it's some C++ pointer from some 3rd-party library that you can't really serialize and gotta keep open, you gotta keep it in memory and manage its lifetime explicitly, be it a REST web server, in Haskell or in a C++ app.