On 10/03/2015 03:01 AM, Henrik Nilsson wrote:
Hi all,
Bardur Arantsson wrote:
I should also say: I certainly *understand* the textbook argument, [...] but this is not a good *general* argument against change.
Just to be clear, Graham and I were not at all arguing against change in general. But we are, in general, urging extreme caution when it comes to non-essential breaking changes.
Measuring breakage by referring to Hackage is just the tip of the iceberg. Much breakage, including proprietary code, books, research papers, what people have learned, is very difficult or impossible to measure. Somehow this point seems to have been forgotten in the present discussion. The reason there has to be really compelling reasons for adopting breaking changes is exactly because the full impact of those breaking changes is very hard to gauge properly. As to this specific proposal, in our opinion, the reasons put forward so far for the "monad of no return" are not very compelling. And therefore it should not be adopted at this point.
Have you surveyed the actual number of books out there which show how to implement Monad instances and how many of them would be affected?
No. we have not. But ought not the burden of proof rest with those who are proposing a non-essential breaking change? If not, why not?
but if we're going that way, then we're going to end up like C++... before C++11/C++14. [...] (stagnatiation)
We are hardly going to end up like C++ in that sense by being very careful before adopting non-essential breaking changes. Or even rule them out. Nor, returning to this specific proposal, is leaving "return" as a method of "Monad" going to mean that Haskell ends up being stagnant.
Further, it is also worth noting that by almost any measure C++ is an extremely successful language despite its warts.
C++ is what "success at all cost" looks like. (I won't bother responding to the rest, others have done that adequately.) Look, I truly[1] do appreciate the arguments in favor of "don't break things", but I don't think it's borne out by any reasonable reading of history. Regards, [1] At least I think I do. :)