They probably mean Haskell. Note: I don't know Haskell, so below is speculation.
To log you need IO. To get IO you need to provide it to the function that will do logging. And now your function has to be marked as doing IO. So now you need to thread all that IO through all your functions, and "turn you code into monadic code" (I think that's the term).
Other languages (like Erlang) don't care, and you can log whenever you want.
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Flamewar off-topic: it looks like hardly anyone is doing any useful logging in Haskell, because if you search for "logging in Haskell" you end up in:
- highly academic discussions on "logging actions" vs "logging of computations"
- extremely convoluted solutions that turn even the simplest examples into a mess
- a couple of libraries whose entire documentation is usually "believe me we're the shit", and if they do have examples, they are an impenetrable mess of custom types and ascii art
For every other language it literally is `logger.info(something)`
And here we see the damage caused by the modern OOP. People that complain about that want to replicate in Haskell the lob4j philosophy of adding logging into every interface, because with data and IO chunked everywhere inside object interfaces, you never know if you can ever repeat an execution in a development environment to verify it.
The thing is, if for some reason you really think you need to log inside a pure function, you either need an intermediate variable or your perceived needs are severely misguided.
> And here we see the damage caused by the modern OOP. People that complain about that want to replicate in Haskell the lob4j philosophy of adding logging into every interface
And here we see a person slinging unsubstantiated accusations
> if for some reason you really think you need to log inside a pure function, you either need an intermediate variable or your perceived needs are severely misguided.
Clear demonstration of "it looks like hardly anyone is doing any useful logging in Haskell".
Because, as we know, the fact that "you can repeat an execution" immediately makes your need to log anything in that execution as "misguided".
Um, what? You can't just drop this without elaborating. I've never seen anybody have problems logging in a functional language.