August 2014 - Haskell-Cafe

Monads vs Linear regions
by Timotej Tomandl 31 Aug '14

31 Aug '14

How do they compare? Can Linear regions handle all uses of monads or does they lack some applications?

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Fwd: Linear regions ("Linear Regions Are All You Need") as the only way of encapsulation of impure state
by Timotej Tomandl 31 Aug '14

31 Aug '14

I was thinking for a while about if other kinds of handling of impure state have any advantages over linear regions. So I thought it will be nice to open the discussion about how does it compare with monads, linear types, uniqueness typing and monadic regions.

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[ANN] codex 0.1.0.4
by Alois Cochard 30 Aug '14

30 Aug '14

Hi Cafe, I just wanted to let you know that I have just released a new version of `codex` on hackage. There is *no new features* in this version, but thanks for the help from Hubert Behaghel I was able to investigate issues with MacOS. So basically this version now work with MacOS, if you had give a try before please delete your "~/.codex" configuration file before installing the new version. Cheers -- *Λ\ois* http://twitter.com/aloiscochard http://github.com/aloiscochard

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ICFP pre-party
by Roman Cheplyaka 30 Aug '14

30 Aug '14

We're having a small unofficial ICFP pre-party today in Gothenburg. All haskell-cafe readers that happen to be in Gothenburg are welcome :-) The plan is to meet at The Bishop's Arms (Kungsportsavenyen 36) at 19.00. NOTE: there are three Bishop's Arms in Gothenburg, so mind the address. Feel free to text me at +380662285780. Roman

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Re: [Haskell-cafe] Using 'lens' for "over"-like computation in Monad
by Nikolay Amiantov 30 Aug '14

30 Aug '14

Thank you! I'm still lost in the forest of all lens functions and generality, and haven't expected this signature. Can someone recommend good reading on all the lens-related types and classes, what they represent and how can they be used? (interested not only in "how", but also "why") 30 авг. 2014 г. 11:20 пользователь "Benno Fünfstück" < benno.fuenfstueck(a)gmail.com> написал: > The lens operator that does this is %%~, also called `traverseOf`: > > λ: ("Hello", "World") & _1 %%~ (\a -> putStrLn a >> return a) > Hello > ("Hello","World") > > Also see the documentation: > http://hackage.haskell.org/package/lens-4.4.0.1/docs/Control-Lens-Traversal… > > -- > Benno > > > 2014-08-30 9:44 GMT+02:00 Nikolay Amiantov <nikoamia(a)gmail.com>: > >> Hello Cafe, >> >> I'm trying to wrap my head around 'lens' library. My current exercise is >> to modify something using Lens in monad. Say, >> >> ("Hello", "World") & _1 `myOp` (\a -> putStrLn a >> return a) >> >> in IO, where myOp would be of type: >> >> myOp :: Monad m => Lens s t a b -> (a -> m b) -> s -> m t >> >> Of course I can write it myself, using combination of "view" and "set": >> >> myOp lens f v = f (view lens v) >>= flip (set lens) v >> >> (have not checked this, but something like that should do), but is there >> a more elegant way? >> >> Nikolay. >> >> _______________________________________________ >> Haskell-Cafe mailing list >> Haskell-Cafe(a)haskell.org >> http://www.haskell.org/mailman/listinfo/haskell-cafe >> >> >

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Using 'lens' for "over"-like computation in Monad
by Nikolay Amiantov 30 Aug '14

30 Aug '14

Hello Cafe, I'm trying to wrap my head around 'lens' library. My current exercise is to modify something using Lens in monad. Say, ("Hello", "World") & _1 `myOp` (\a -> putStrLn a >> return a) in IO, where myOp would be of type: myOp :: Monad m => Lens s t a b -> (a -> m b) -> s -> m t Of course I can write it myself, using combination of "view" and "set": myOp lens f v = f (view lens v) >>= flip (set lens) v (have not checked this, but something like that should do), but is there a more elegant way? Nikolay.

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"Hackathon"
by Richard Eisenberg 30 Aug '14

30 Aug '14

Hi Cafe, In my experience, "hackathon" can refer to two very different sorts of events: hacking marathons (such as jacobsHack), where participants tend to work overnight to accomplish something amazing in a limited time; and hacker weekends (such as Hac Phi), where participants work on projects, socialize, and then (presumably) rest at night. Both of these sorts of events have their place in the world, and I'm in no way suggesting one is "better" than the other. But, I do think it be good for all of us to name them differently, so folks know what they are signing up for. In particular, I'm worried that calling hacker weekends "hackathons" may discourage those of us with outside, inflexible commitments (e.g. kids; the need for 8 hours of sleep) from attending. Conversely, folks looking for the higher-energy environment of an all-night marathon might be disappointed to show up at a hacker weekend. What do you think? Is this distinction pointless? Would being consistent about this difference help? Here are some proposed new names for hacker weekends: - Hacker weekend - Hacker meetup - Community Hack - Weekend of Haskell I personally favor reserving the term "hackathon" for the marathon events. Richard

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Problem finding rewrite rules
by Dominik Peteler 30 Aug '14

30 Aug '14

Dear Cafe, I'm currently looking at the optimization GHC is doing and I cannot find the rewrite rules it fires. When I run my test code with ghc -O2 -ddump-simpl-stats -ddump-rule-firings Main.hs GHC shows the rules which are fired: ... Rule fired: Class op + ... Rule fired: +## ... and so on. Nothing new, nothing special. However, where do I find the definitions of these rules ? I grepped[1] the GHC code base and found nothing so far. I didn't find any documentation on it either. Can anyone point me to some place where I can find further information ? Thank you folks and have a nice day Dominik PS.: Since I'm working on numerical stable code with directed rounding I'm only interested in these two particular rules. I suspect them to break parts of my code. [1] http://jamie-wong.com/2013/07/12/grep-test

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Master's thesis topic and mentor
by Konstantin Saveljev 30 Aug '14

30 Aug '14

Hello, *short summary*: I am looking for someone who might have a topic for Master's thesis and will be interested in mentoring me along the way (giving pointers, helping here and there but not doing everything for me) *more detailed*: I have been introduced to Haskell about a year ago. It's been a slow ride, but I am gaining knowledge step by step. I am having some difficulty in finding a topic for my Master's degree and thought it would benefit me to try doing something Haskell related (be it a library, some part of a project or something similar). Unfortunately I do not believe I am able to pick something up by myself. Therefore I am looking for someone out there who might just have something to do they would be interested in delegating to somebody else and helping a bit throughout that work (and it cannot be something too easy, as there are some expectations from the work done for Master's degree) . It might be a long shot but I believe it is worth trying. Thank you for your time. Best regards, Konstantin Saveljev

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Does web-based email harm mailman lists?
by Kim-Ee Yeoh 29 Aug '14

29 Aug '14

Beautiful haskell people, Ever noticed the lacunae on some list threads? Someone hits reply and instead of reflecting via mailman, it goes direct to OP. OP notices absence of To:haskell-cafe and adds it back in in their reply to the reply. End result? The thread looks like OP having a convo with themselves. Unless you look at the quoted parts, which you have to click to reveal in web-based email. The convention, say with a google-groups based mailing list, is that conversations in mailing list are public by default. With some manual C&P, you can email responses in private. For cafe participants using web-based email, the situation is reversed, through no fault of their own. Approx 18 months ago, the haskell-beginners list suffered the same problem [1]. After some digging, it looks like there's a configurable option to Do The Right Thing: http://ccit.mines.edu/Mailman-FAQ#25 I was also privately emailed that there are downsides I wasn't aware of: Reply-To Munging Considered Harmful http://www.unicom.com/pw/reply-to-harmful.html Reply-To Munging Considered Useful http://www.metasystema.org/essays/reply-to-useful.html So what happened in the aftermath? Not much that I can tell. Everything just purred along. Now you might argue that haskell-cafe will just purr along grandly as well given the status quo. But this is a wrinkle that probably needs some awareness at least, hence this email. Would you like this fixed? The list owner would need to be obliged upon. [1] http://www.haskell.org/pipermail/beginners/2013-January/011304.html -- Kim-Ee

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