Note: I realize nobody is directly saying that we should use (++) instead of (<>) in this conversation just yet, but I want to clear a few things up.
One of the early options when the operator (<>) was coined was to try to say we should just generalize the type of (++) instead to make it mappend. (Note: it originally was mplus, in a Haskell version long long ago, so it keeps getting repurposed!) Unfortunately, this plan ran afoul of the fact that the primary libraries using the (<>) notation at the time (pretty printing libraries) also mixed it heavily with (++), exploiting the different fixities involved. (Finding a decent fixity for (<>) was a huge chunk of the conversation at the time.) There is a deliberate fixity difference between (++) and (<>), a good chunk of code out there mixes them that deals with pretty printing that would break pretty horribly if we just outright removed (++), and trying to do a visual search and replace for (++) with (<>) in light of them having different fixities is a very error prone process, so we aren't currently planning on deprecating the existing (++) operator any time soon. At least, nobody has put a proposal to the core libraries committee to that end. Since the call was made to make (<>) become the new operator, we ultimately decided to leave (++) untouched, even though it could be generalized to match (<>), for much the same reason that map still exists, despite there being a more general fmap: Ultimately, there isn't a reasonable migration plan to make (++) or map become the way you define the instance involved, and at least this way the name duplication can be leveraged by the folks who want a less polymorphic combinator. Would the world be a little tidier without map or (++) hanging about? Sure. But the hate mail levels in my inbox would skyrocket commensurately. ;) -Edward On Mon, Jul 3, 2017 at 5:01 PM, Erik de Castro Lopo <[email protected]> wrote: > Vassil Ognyanov Keremidchiev wrote: > > > What do you think of making (++) the same as (<>) so we could use ++ as > > concatenation of any monoid, not just lists in Haskell 2020? > > This will be more intuitive for beginners, too. > > Two symbolic operators that are synonymous seems a bit of a waste. I would > much rather see (++) be deprecated in favour of (<>). At work we have a > custom prelude which already does this. > > Erik > -- > ---------------------------------------------------------------------- > Erik de Castro Lopo > http://www.mega-nerd.com/ > _______________________________________________ > Haskell-prime mailing list > [email protected] > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-prime >
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