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Simplify your code: Functional core, imperative shell

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Re: Simplify your code: Functional core, imperative shell

#71

Post by whstl »

taeric wrote: post #65
whstl wrote: post #58

Earlier quoted context omitted.

> but even in those, you typically have the more imperative operations as the lower levels 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…

I have not seen too many (any?) times where the monad trick is done in such a way that they don't combine everything in a single context wrapper and talk about the "abnormal" case where things don't complete during execution. 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.)

You would deal with this problem in the same way you would with, say, in a REST API.

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.

Re: Simplify your code: Functional core, imperative shell

#72

Post by lmm »

hackthemack wrote: post #4

I never liked encountering code that chains functions calls together like this email.bulkSend(generateExpiryEmails(getExpiredUsers(db.getUsers(), Date.now()))); Many times, it has confused my co-workers when an error creeps in in regards to where is the error happening and why? Of course, this could just be because I have always worked with low effort co-workers, hard to say. I have to wonder if programming should ha…

> I have to wonder if programming should have kept pascals distinction between functions that only return one thing and procedures that go off and manipulate other things and do not give a return value.

What you want is to use a language that has higher-kinded types and monads so that functions can have both effects (even multiple distinct kinds of effects) and return values, but the distinction between the two is clear, and when composing effectful functions you have to be explicit about how they compose. (You can still say "run these three possibly-erroring functions in a pipeline and return either the successful result or an error from whichever one failed", but you have to make a deliberate choice to).

Re: Simplify your code: Functional core, imperative shell

#76

Post by kaashif »

droningparrot wrote: post #75

Haskell practically encourages this style of programming. Any function that touches IO needs to wrap outputs with an appropriate monad. It becomes easier to push all IO out to the edges of your program and keep your core purely functional with no monads

I wish that's what people did, some codebases I've seen are messes of monad transformer stacks the likes of which you've never seen.

I mean, what if you want to do IO and have mutable data structures inside a do block? I'm afraid I'm going to have to prescribe you a monad transformer. Be careful of the side effects.

Re: Simplify your code: Functional core, imperative shell

#77

Post by kmeisthax »

droningparrot wrote: post #75

Haskell practically encourages this style of programming. Any function that touches IO needs to wrap outputs with an appropriate monad. It becomes easier to push all IO out to the edges of your program and keep your core purely functional with no monads

Maybe JavaScript's colored functions[0] were trying to tell us something

[0] https://journal.stuffwithstuff.com/2015/02/01/what-color-is-...

Re: Simplify your code: Functional core, imperative shell

#79

Post by ccortes »

QuadmasterXLII wrote: post #73

I would argue that the real key is to have a distinct core and shell, and to hold the core to a much higher standard of quality than the shell. In this article, being "functional" is just serving as a proxy for code quality.

> In this article, being "functional" is just serving as a proxy for code quality.

It is not, it is being very specific about what it means and what it is referring to

Re: Simplify your code: Functional core, imperative shell

#80

Post by sandeepkd »

hackthemack wrote: post #4

I never liked encountering code that chains functions calls together like this email.bulkSend(generateExpiryEmails(getExpiredUsers(db.getUsers(), Date.now()))); Many times, it has confused my co-workers when an error creeps in in regards to where is the error happening and why? Of course, this could just be because I have always worked with low effort co-workers, hard to say. I have to wonder if programming should ha…

On the same page here, read it multiple times to see if I can convince my mind, this is bit off in terms of reading the code as its being executed. There are high chances of people making mistakes over the time with such patterns. As usual there is always a trade off involved, readability is the one taking hit here.
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