On 13 February 2016 at 08:32, Christopher Allen <c...@bitemyapp.com> wrote:
> Prelude> let myList = [1, 2, 3 :: Integer] > Prelude> let myList' = myList ++ undefined > Prelude> :t myList > myList :: [Integer] > Prelude> :t myList' > myList' :: (?callStack::GHC.Stack.Types.CallStack) => [Integer] > Yes, and I think perhaps an even more worrying problem here is that by adding the reference to undefined, myList went from being a thunk to being a function. That is, it will be re-evaluated each time it it used. I made a ticket about this: https://ghc.haskell.org/trac/ghc/ticket/11383 Cheers Simon > This is on by default and insofar as I've been able to try, it's avoidable > in a default GHCi 8.0 REPL session. I'm glad I caught this before our book > goes to print in a couple months. We'd managed to avoid talking about > implicit parameters in 1,100+ pages of book but now we're forced to > acknowledge their existence in the 4th of 32 chapters. > > This slipped past the radar more stealthily than the earlier stages of BBP > did for 7.10. I was hearing about BBP on the GHC Trac pretty early on for > months on end. Was the thinking that people still used implicit parameters > for anything or taught them? On the one hand, this is a nice change and > something I personally attempted (and failed) to make easier in GHC 7.10. > The implementation making the types noisy rankles and didn't seem necessary > when I investigated it between 7.8 and 7.10. > > Could you warn us when (educationally relevant?) stuff like this is coming > down the pipe before the RC please? Ideally during the design phase. I > think this was discussed as part of FTP to avoid future debacles. > > This isn't just a pedagogical problem, this is a UX problem. The users > don't _care_ that call stack information is being carried around. Why would > they? It happens without any mention in the types in almost every other > programming language. > > > --- Chris Allen > > > _______________________________________________ > ghc-devs mailing list > ghc-devs@haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/ghc-devs > >
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