[valenterry]

Not that I'm a fan of Haskell, but I believe that if this log is critical to the behavior of the program AND it is inserted in a place where important effects have previously not been expected (such as pure mathematical calculations) then it is a good thing that the language makes you aware of that. Someone might for example be caching/memorizing those calculations and suddenly your log isn't always executed and that might be a bug.

I much rather prefer to evaluate the impact in advance rather than having to find and figure it in production.

[dmitriid]

> I much rather prefer to evaluate the impact in advance rather than having to find and figure it in production.

See, this is exactly the zealotry and demagoguery I am talking about.

99% of use cases: we need to add a single line of logging here

Pure functional programming cultists: first we must consider the semantics of the program and the implication of logging on the grand scheme of things. Consider the criticality of a log line. What is a log line? ... <two hours later> ... an lo, once you've done the refactoring to consider the co-variants ... <another two hours later>

Edit. I'll reiterate:

Easy-to-use concurrency primitives, effortless parallelisation and concurrency, and even the most basic stuff like ability to put a logging statement anywhere in the code without re-engineering half of your program trump whatever imagined advantages of pure functional programming you may come up with. Any day of the week, and twice on Fridays.

[valenterry]

If you need hours to figure out if a log line is relevant or not, then you have much more important problems to take care of.

For example, if this is a log line for audit logging in an enterprise product then it's clearly relevant. If this is a trace log line in case you need to debug some minor issue, then that's a different story. Has nothing to do with zealotry, just common sense. If you don't understand that there is a difference between those two cases then the discussion ends for me here.

[dmitriid]

> If you need hours to figure out if a log line is relevant or not, then you have much more important problems to take care of.

I don't.

> Has nothing to do with zealotry, just common sense.

Ah yes. "does it change the semantics of your (whole) program if that logline, that you are talking about, is not executed for some reason - or if it is executed more than once?" vs. "this logline is critical and will be e.g. parsed and used by another system and actions might be taken due to it, then I would argue it is good if you are forced to consider the potential impacts to your program. "

etc. etc.

And yet the fact is that if you need to log something your precious "mah purity" function is doing, you're stuck with "sometimes a couple of 100 lines need to be rewritten".

Where as non-cultists just do a `Log.info` etc.

If you can't understand that, well :shrug:

Edit. I just re-read that inane pseudo philosphical bullshit about "the semantics of the whole program a log line". No, I definitely don't need to consider the semantics of the whole program to add a bloody log line.