Re: [Haskell-cafe] abs minBound (0 :: Int) negate minBound == (minBound :: Int)
fact 0 = 1 fact n = n * fact (n-1) Now I ran it as fact 100 with signature Int - Int and with Integer - Integer In the first case I got 0 in about 3 seconds [...] And if that sounds like a unreal argument, consider representing and storing Graham's number. So, since computers are finite anyway, we can just arbitrarily (well, almost) redefine large constants, and set all factorials above some threshold to zero? Perhaps we should also set pi=3, that would simplify lots of things :-) Pragmatically: 32-bits is unwise for a bank-balance, 64 should be a bit more safe Please start a bank using modulo arithmetic, I'm looking forward to overdrafting my account! So yes, Haskell's Int, should have been called FastInt or Int29 or somethin' On a more serious note, I accept that Int (and other limited precision numbers) is a fact of life, and sometimes useful for performance reasons. I would have liked, however, to have a compiler option or some other way to make my programs throw an exception on overflow - even if this turned out to be slower, I could at least use it when testing my programs, which would have caught a few bugs. -k -- If I haven't seen further, it is by standing in the footprints of giants ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] GHC and backwards compatibility
If you use $ cabal install --constraint=array installed then cabal-install is forced to use the installed version of array. If a package conflicts with this version, then it will report the conflicting packages. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] abs minBound (0 :: Int) negate minBound == (minBound :: Int)
On Wed, Aug 21, 2013 at 11:47 AM, Ketil Malde ke...@malde.org wrote: On a more serious note, I accept that Int (and other limited precision numbers) is a fact of life, and sometimes useful for performance reasons. I would have liked, however, to have a compiler option or some other way to make my programs throw an exception on overflow - even if this turned out to be slower, I could at least use it when testing my programs, which would have caught a few bugs. Yes for software detection, some will want it and some will not; see the same discussion a few months ago http://www.haskell.org/pipermail/haskell-cafe/2013-June/107153.html The 'some other way' is hardware detection. And there is glimmer of hope that Intel may begin to do due diligence http://www.emulators.com/docs/LazyOverflowDetect_Final.pdf ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] PPC binaries for GHC 7.x?
Does anyone have PPC binaries for GHC 7.x? I've been trying to help a PPC user compile a large haskell application, and it (and it's dependencies) require a newer ghc; the latest ppc binaries we've found are for 6.10, and we have been unable to compile a never ghc from source (6.12 /almost/ worked, but eventually failed with a linker error that appears to be unsolvable in the near-term). Thanks! Rogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PPC binaries for GHC 7.x?
On Wed, Aug 21, 2013 at 4:55 AM, Rogan Creswick cresw...@gmail.com wrote: Does anyone have PPC binaries for GHC 7.x? I've been trying to help a PPC user compile a large haskell application, and it (and it's dependencies) require a newer ghc; the latest ppc binaries we've found are for 6.10, and we have been unable to compile a never ghc from source (6.12 /almost/ worked, but eventually failed with a linker error that appears to be unsolvable in the near-term). What operating system? Debian Wheezy (stable) supports PowerPC, and has a working GHC 7.4.1. You can also try unstable (sid). Don't install sid packages on stable (I ran into linker errors with direct-sqlite when I tried that). ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] PPC binaries for GHC 7.x?
On Wed, Aug 21, 2013 at 2:29 AM, Joey Adams joeyadams3.14...@gmail.comwrote: What operating system? Oh, I should have specified -- OS X (I'm not certain which version of OS X; probably not particularly new) --Rogan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas on a fast and tidy CSV library
Dear All, I now have some example code. I have put it on: http://pastebin.com/D9MPmyVd. vectorBinner is simply of type Vector Int - Int. I am inputting a 1.5GB CSV on stdin, and would like vectorBinner to run over every single record, outputting results as computed, thus running in constant memory. My programme instead quickly approaches full memory use. Is there any way to work around this? Justin On 25 July 2013 17:53, Johan Tibell johan.tib...@gmail.com wrote: You can use the Incremental or Streaming modules to get more fine grained control over when new parsed records are produced. On Thu, Jul 25, 2013 at 11:02 AM, Justin Paston-Cooper paston.coo...@gmail.com wrote: I hadn't yet tried profiling the programme. I actually deleted it a few days ago. I'm going to try to get something new running, and I will report back. On a slightly less related track: Is there any way to use cassava so that I can have pure state and also yield CSV lines while my computation is running instead of everything at the end as would be with the State monad? On 23 July 2013 22:13, Johan Tibell johan.tib...@gmail.com wrote: On Tue, Jul 23, 2013 at 5:45 PM, Ben Gamari bgamari.f...@gmail.com wrote: Justin Paston-Cooper paston.coo...@gmail.com writes: Dear All, Recently I have been doing a lot of CSV processing. I initially tried to use the Data.Csv (cassava) library provided on Hackage, but I found this to still be too slow for my needs. In the meantime I have reverted to hacking something together in C, but I have been left wondering whether a tidy solution might be possible to implement in Haskell. Have you tried profiling your cassava implementation? In my experience I've found it's quite quick. If you have an example of a slow path I'm sure Johan (cc'd) would like to know about it. I'm always interested in examples of code that is not running fast enough. Send me a reproducible example (preferably as a bug on the GitHub bug tracker) and I'll take a look. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas on a fast and tidy CSV library
As I mentioned, you want to use the Streaming (or Incremental) module. As the program now stands the call to `decode` causes 1.5 GB of CSV data to be read as a `Vector (Vector Int)` before any encoding starts. -- Johan On Wed, Aug 21, 2013 at 1:09 PM, Justin Paston-Cooper paston.coo...@gmail.com wrote: Dear All, I now have some example code. I have put it on: http://pastebin.com/D9MPmyVd . vectorBinner is simply of type Vector Int - Int. I am inputting a 1.5GB CSV on stdin, and would like vectorBinner to run over every single record, outputting results as computed, thus running in constant memory. My programme instead quickly approaches full memory use. Is there any way to work around this? Justin On 25 July 2013 17:53, Johan Tibell johan.tib...@gmail.com wrote: You can use the Incremental or Streaming modules to get more fine grained control over when new parsed records are produced. On Thu, Jul 25, 2013 at 11:02 AM, Justin Paston-Cooper paston.coo...@gmail.com wrote: I hadn't yet tried profiling the programme. I actually deleted it a few days ago. I'm going to try to get something new running, and I will report back. On a slightly less related track: Is there any way to use cassava so that I can have pure state and also yield CSV lines while my computation is running instead of everything at the end as would be with the State monad? On 23 July 2013 22:13, Johan Tibell johan.tib...@gmail.com wrote: On Tue, Jul 23, 2013 at 5:45 PM, Ben Gamari bgamari.f...@gmail.com wrote: Justin Paston-Cooper paston.coo...@gmail.com writes: Dear All, Recently I have been doing a lot of CSV processing. I initially tried to use the Data.Csv (cassava) library provided on Hackage, but I found this to still be too slow for my needs. In the meantime I have reverted to hacking something together in C, but I have been left wondering whether a tidy solution might be possible to implement in Haskell. Have you tried profiling your cassava implementation? In my experience I've found it's quite quick. If you have an example of a slow path I'm sure Johan (cc'd) would like to know about it. I'm always interested in examples of code that is not running fast enough. Send me a reproducible example (preferably as a bug on the GitHub bug tracker) and I'll take a look. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Google co-sponsoring ZuriHac 2013
Dear Haskellers, I would like to remind you that the Zurich FP Afternoon (with a keynote by Simon Marlow) is taking place next week (13:00, Thursday, 29 August) and is directly followed by the ZuriHac 2013 Haskell Hackathon [1]. There are still some places available at both events -- you're welcome to register at: http://bit.ly/ZuriHac2013Reg Google Switzerland will co-sponsor the FP Afternoon and ZuriHac 2013 together with ETH Zurich and Erudify. Their sponsorship means we can give each attendee a free t-shirt (picture on the wikipage [2]) and free food and drinks during the FP Afternoon. Google is also offering a quiz during the FP Afternoon with prizes including a Galaxy S4 mini. I hope to see you there! Bas [1] http://www.haskell.org/haskellwiki/ZuriHac2013 [2] http://www.haskell.org/haskellwiki/ZuriHac2013#News ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] haskore - lilypond - typesetting?
I tried using lilypond ( http://www.lilypond.org/ ) for typesetting of sheet music. While the output looks nice, the input language IMHO is quite horrible, because the underlying data/execution model is underspecified. For some parts, it tries to describe the logical structure of the score; but for others, the layout; and in addition it has several non-obvious context-dependencies (but see below), preventing modularity. Is there a better option? E.g., starting from a clear mathematical model, as in Haskore, and use lilypond only as a PDF rendering engine? Do I want hly / hts perhaps? http://rd.slavepianos.org/?t=hly As I see it, the main high-level design problem is that the source language needs partial evaluation annotations for abstractions applications: sometimes they should be expanded (for MIDI rendering, always) and sometimes not (in typesetting, to create repetition marks instead of actually repeating notes). PS: I agree that some of lilypond's context dependencies (relative pitch, implicit note length) do really save large amounts of tedious typing: c4 e g a c1 is much more economical than [c 1 qn, e 1 qn, g 1 qn , a 1 qn, c 2 fn] which I guess is the Haskore equivalent. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskore - lilypond - typesetting?
On Wed, Aug 21, 2013 at 6:35 PM, Johannes Waldmann waldm...@imn.htwk-leipzig.de wrote: I tried using lilypond ( http://www.lilypond.org/ ) for typesetting of sheet music. While the output looks nice, the input language IMHO is quite horrible, I use musescore. Its got 3 modes on entry a. clickety-click -- ie mouse b. keyboard shortcuts c. midi keyboard For bulk entry direct entry from a midi keyboard is best http://musescore.org/en/handbook/note-entry [Since I am not much of a musician, I usually hover between a and b] If after that you want the lilypond toolchain, it will export to lilypond and then use your favorite text editor. [Not sure of the quality of export] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] abs minBound (0 :: Int) negate minBound == (minBound :: Int)
but Integer is actually (if you're using GMP with your ghc): Yes, that's tolerably well known. You only pay the space overhead when you need it (like Lisp or Smalltalk). But you always pay the time overhead. I thought Integers can't be unboxed, regardless of their magnitude? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What am I missing? Cycle in type synonym declarations
GHC tries to typecheck quotations. In this case it's trying to typecheck the
declaration
type Bar = FooT $t
Part of type checking is rejecting recursive type synonyms. Here GHC is
rejecting it because it *might* be recursive, depending on how $t is filled in.
The trouble is that we really *can't* typecheck partial declarations like this
one. All this will be fixed when we fold in the new Template Haskell story
(it'll be in 7.8). See my blog post on the GHC Trac (from about 2 yrs ago)
describing the change. (I'm on a train so don't know the URL.) Geoff has made
the change... it just needs to be merged in.
Simon
| -Original Message-
| From: Haskell-Cafe [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of
David
| Fox
| Sent: 20 August 2013 22:00
| To: Haskell Cafe
| Subject: [Haskell-cafe] What am I missing? Cycle in type synonym declarations
|
| This file gives me the error Cycle in type synonym declarations Can
| anyone tell me why? I'm just trying to write a function to create a
| type that is a FooT with the type parameter fixed.
|
| {-# LANGUAGE TemplateHaskell #-}
| import Language.Haskell.TH (Q, Dec, TypeQ)
|
| data FooT a = FooT a
|
| foo :: TypeQ - Q [Dec]
| foo t = [d| type Bar = FooT $t |]
|
| ___
| Haskell-Cafe mailing list
| Haskell-Cafe@haskell.org
| http://www.haskell.org/mailman/listinfo/haskell-cafe
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Re: [Haskell-cafe] haskore - lilypond - typesetting?
I think the big question is whether you are dealing with music or scores. a .ly file represents not the music, but the music plus typographic annotations (and I find that even lilypond quite often benefits from hints). Most gui programs represent scores, but I think lilypond stands alone in that among text formats. So the question, to me, is whether you need a representation of music, or of a score; if of music, I would choose an input format other than lilypond (abc recommends itself from my folk-music background), using an appropriate backend for rudimentary typesetting. But if you need the full layout flexibility, I doubt you can beat writing straight lilypond: I have yet to see a frontend produce easily hand-edited lilypond source (which I find very quickly becomes a featureless blob without judicious use of whitespace), nor one that exposes the flexibility of the lilypond engine (and I find lilypond much faster to write than Finale, and little slower than Mozart's superb keyboar d entry (not being a keyboardist, I cannot speak for midi entry)). haskore and hly I would reserve for internal representations for conversion or transformation programs; I think there are much better alternatives for human writing. I would also be careful with excessively mathematical representations; before finding lilypond, I had to discard more than one program for failure to handle irregular meters. From: Haskell-Cafe [haskell-cafe-boun...@haskell.org] on behalf of Rustom Mody [rustompm...@gmail.com] Sent: Wednesday, August 21, 2013 10:46 AM To: Johannes Waldmann Cc: Haskell Cafe Subject: Re: [Haskell-cafe] haskore - lilypond - typesetting? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] haskore - lilypond - typesetting?
Here's one I did earlier... http://www.flickr.com/photos/44929957@N03/4459628487/lightbox/ This is Haskore implementation of Chick Corea's Child Song 6 rendered to LilyPond - I don't imagine Mr. Corea's publishers will be sending me a takedown request any time soon. There's a lot missing from Haskore that is needed to make good scores - the renderer of the above took a lot of effort with metrical grouping but the result is still abysmal. I doubt mathematics can help (common practice) music typesetting much - Western notation has had a thousand years to develop without the constraint of a regular syntax; so if Lilypond is horrible it is mostly the fault of what it tries to typeset (it does make some unwarranted mistakes like over-restricting the characters it can use for variable names and its parenthesizing is horrible). On 21 August 2013 14:05, Johannes Waldmann waldm...@imn.htwk-leipzig.dewrote: I tried using lilypond ( http://www.lilypond.org/ ) for typesetting of sheet music. While the output looks nice, the input language IMHO is quite horrible, because the underlying data/execution model is underspecified. For some parts, it tries to describe the logical structure of the score; but for others, the layout; and in addition it has several non-obvious context-dependencies (but see below), preventing modularity. Is there a better option? E.g., starting from a clear mathematical model, as in Haskore, and use lilypond only as a PDF rendering engine? Do I want hly / hts perhaps? http://rd.slavepianos.org/?t=hly As I see it, the main high-level design problem is that the source language needs partial evaluation annotations for abstractions applications: sometimes they should be expanded (for MIDI rendering, always) and sometimes not (in typesetting, to create repetition marks instead of actually repeating notes). PS: I agree that some of lilypond's context dependencies (relative pitch, implicit note length) do really save large amounts of tedious typing: c4 e g a c1 is much more economical than [c 1 qn, e 1 qn, g 1 qn , a 1 qn, c 2 fn] which I guess is the Haskore equivalent. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HSpec vs Tasty (was: ANN: hspec-test-framework - Run test-framework tests with Hspec)
So is there a high-level comparison of HSpec and tasty? The only difference I've glimpsed so far was that HSpec has a syntactic sugar for describing tests which, honestly, I haven't found very useful. So, could someone write up a quick comparison of the two for the benefit of the folks like me who have a lot of test-framework tests and have to switch to either tasty or hspec? On 08/18/2013 06:27 PM, Roman Cheplyaka wrote: My answer to this and many similar questions regarding tasty is: - I am probably not going to work on this - but I would be happy to see someone doing it Note that hspec-test-framework is a separate package, and it didn't have to be written or even approved by Simon. Same here — please write more supplementary packages if you feel a need. Roman * Alfredo Di Napoli alfredo.dinap...@gmail.com [2013-08-18 15:18:07+0200] Hi Simon, this is an exciting news! May I ask the question that maybe is lurking in the shadow? Due to the recent announcement of Roman's tasty library, are there plans to basically release something similar to hspec-test-framework and hspec-test-framework-th but targeting tasty instead? Bye :) A. On 18 August 2013 14:50, Simon Hengel s...@typeful.net wrote: Hi, I just released hspec-test-framework[1] and hspec-test-framework-th[2] to Hackage. They can be used to run test-framework tests with Hspec unmodified. This can also be used to work around test-framework's incompatibility with QuickCheck-2.6 and base-4.7.0 ;) Have a look at the README for usage instructions: https://github.com/sol/hspec-test-framework#readme Cheers, Simon [1] http://hackage.haskell.org/package/hspec-test-framework [2] http://hackage.haskell.org/package/hspec-test-framework-th ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Yet Another Forkable Class
TLDR: New forkable monad/transformer suggestion http://pastebin.com/QNUVL12v(hpaste is down) Hi, There are a dozen packages on hackage defining a class for monads that can be forked, however none of these are modular enough to be useful in my opinion. In particular the following are not addressed: 1. Cases when the child thread's monad is different from the parent's 2. Monad transformers (this is somewhat addressed with Control.Monad.Trans.Control) I will try to demonstrate both issues with an example. 1. WebSockets WebSockets is a monad that cannot itself be forked. This is because at any given time there should only be a single thread listening on a websocket. However there is a reasonable monad that can be forked off, namely one that can send to the websocket - one that has access to the Sink. So first off a Forkable class should not look like this: class (MonadIO m, MonadIO n) = Forkable m where fork :: m () - m ThreadId But rather like this: class Forkable m n where fork :: n () - m ThreadId For our example the instance would be instance (Protocol p) = Forkable (WebSockets p) (ReaderT (Sink p) IO) where fork (ReaderT f) = liftIO . forkIO . f = getSink Another example would be a child that should not be able to throw errors as opposed to the parent thread. 2. ReaderT Continuing from the previous example to demonstrate the need to distinguish forkable transformers. Say we have some shared state S that both parent and child should have access to: type Parent p = ReaderT (TVar S) (WebSockets p) type Child p = ReaderT (TVar S) (ReaderT (Sink p) IO) The forkability of Child from Parent should be implied, however with Forkable we have to write a separate instance. So what I suggest is a second class: class ForkableT t where forkT :: (Forkable m n) = t n () - t m ThreadId And then: instance ForkableT (ReaderT r) where forkT (ReaderT f) = ReaderT $ fork . f We can also introduce a default for Forkable that uses a ForkableT instance: class (MonadIO m, MonadIO n) = Forkable m n where fork :: n () - m ThreadId default fork :: ForkableT t = t n () - t m ThreadId fork = forkT instance (Forkable m n) = Forkable (ReaderT r m) (ReaderT r n) This means Child is automatically Forkable from Parent, no need to write a specific case for our specific monads (and if we newtype it we can use -XGeneralizedNewtypeDeriving) Note how MonadTransControl already solves the specific problem of lifting a forking operation into ReaderT. However consider ResourceT from Control.Monad.Resource: it is basically a ReaderT, however in order to safely deallocate resources when sharing reference counting is needed. This means a simple lift would not suffice. We can nevertheless provide a default ForkableT based on MonadTransControl: class ForkableT t where forkT :: (Forkable m n) = t n () - t m ThreadId default forkT :: (MonadTransControl t, Forkable m n) = t n () - t m ThreadId forkT t = liftWith $ \run - fork $ run t return () Actually resourcet's reference counting resourceForkIO also nicely demonstrates the first problem: type Parent p = ResourceT (WebSockets p) type Child p = ResourceT (ReaderT (Sink p) IO) Note how we cannot use resourceForkIO without touching the underlying monads. What do you think? Is there already an established way of modular forking? I wouldn't like to litter hackage with another unusable Forkable class:) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Haskell Weekly News: Issue 277
Welcome to issue 277 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of August 11 to 17, 2013. Quotes of the Week * psygnisfive: Seminearring is the task of giving seminars. * Taneb: You know you've made it when SPJ asks you for help with Haskell. * byorgey: . o O ( For my next trick, I will CPS-encode this rabbit! -- edwardk ) * shachaf: I prefer the cogolden rule: When CPS-transforming, doubt. * edwardk: You see these scars? I got them back in 7.7. * danharaj: parsing is hard, let's go shopping Top Reddit Stories * Mio: A High-Performance Multicore IO Manager for GHC [pdf] Domain: haskell.cs.yale.edu, Score: 147, Comments: 31 On Reddit: [1] http://goo.gl/ZTy1Yl Original: [2] http://goo.gl/6foNWC * Destroying Performance with Strictness Domain: neilmitchell.blogspot.ru, Score: 92, Comments: 45 On Reddit: [3] http://goo.gl/1rkx3a Original: [4] http://goo.gl/rb5UnM * A great series of posts on the power of monoids Domain: self.haskell, Score: 78, Comments: 10 On Reddit: [5] http://goo.gl/TmAAwT Original: [6] http://goo.gl/TmAAwT * Cellular Automata by Edward Kmett Domain: fpcomplete.com, Score: 69, Comments: 7 On Reddit: [7] http://goo.gl/EIFK5A Original: [8] http://goo.gl/03mNhV * Elm 0.9 - New type checker, much better error messages Domain: elm-lang.org, Score: 50, Comments: 14 On Reddit: [9] http://goo.gl/ngSBPX Original: [10] http://goo.gl/4Jp3l6 * Revisiting Matrix Multiplication, Part I by Edward Kmett Domain: fpcomplete.com, Score: 45, Comments: 4 On Reddit: [11] http://goo.gl/gYfm5S Original: [12] http://goo.gl/bg75ZX * Revisiting Matrix Multiplication, Part II by Edward Kmett Domain: fpcomplete.com, Score: 37, Comments: 9 On Reddit: [13] http://goo.gl/qU2r69 Original: [14] http://goo.gl/5cRq72 * Roles: a new feature of GHC (patch GND + type families) Domain: typesandkinds.wordpress.com, Score: 34, Comments: 28 On Reddit: [15] http://goo.gl/HhVOTu Original: [16] http://goo.gl/Twx5YB * Type Inference, Haskell and Dependent Types :: PDF Domain: personal.cis.strath.ac.uk, Score: 33, Comments: 0 On Reddit: [17] http://goo.gl/MbtYGO Original: [18] http://goo.gl/uOx01F * Embedded Languages for High-Performance Computing [Chakravarty, PDF 70 slides] Domain: speakerdeck.com, Score: 31, Comments: 4 On Reddit: [19] http://goo.gl/mb2frN Original: [20] http://goo.gl/EEG0Wk * Graph drawing with gloss Domain: mazzo.li, Score: 30, Comments: 7 On Reddit: [21] http://goo.gl/j0CZmo Original: [22] http://goo.gl/5ZtFuu * Benchmarking sqlite-simple against Python and C Domain: nurpax.github.io, Score: 28, Comments: 9 On Reddit: [23] http://goo.gl/CNyjWa Original: [24] http://goo.gl/gFmWgT * What is lifting? Explained on stackoverflow Domain: stackoverflow.com, Score: 25, Comments: 7 On Reddit: [25] http://goo.gl/HzXWb9 Original: [26] http://goo.gl/hQxTce * GHC API: Interpreted, compiled and package modules Domain: parenz.wordpress.com, Score: 23, Comments: 0 On Reddit: [27] http://goo.gl/xUeUYq Original: [28] http://goo.gl/llQsyE * Time to start writing on the new binding: SDL 2.0 release. Domain: lists.libsdl.org, Score: 22, Comments: 15 On Reddit: [29] http://goo.gl/G0ut36 Original: [30] http://goo.gl/MuO1uB * FP Complete's Haskell programming competition now accepting entries Domain: fpcomplete.com, Score: 21, Comments: 7 On Reddit: [31] http://goo.gl/tbEBKG Original: [32] http://goo.gl/ADsrJ * Pretext by experiments and guesses Domain: fpcomplete.com, Score: 18, Comments: 15 On Reddit: [33] http://goo.gl/oVpKIe Original: [34] http://goo.gl/2PFthz Top StackOverflow Questions * Haskell random numbers suddenly start to “converge” after months of running votes: 30, answers: 1 Read on SO: [35] http://goo.gl/oxUAQ5 * Why does ghc generate so many useless-looking nested case expressions? votes: 10, answers: 1 Read on SO: [36] http://goo.gl/6cdTd1 Until next time, [37]+Daniel Santa Cruz References 1. http://haskell.cs.yale.edu/wp-content/uploads/2013/08/hask035-voellmy.pdf 2. http://www.reddit.com/r/haskell/comments/1k6fsl/mio_a_highperformance_multicore_io_manager_for/ 3. http://neilmitchell.blogspot.ru/2013/08/destroying-performance-with-strictness.html 4. http://www.reddit.com/r/haskell/comments/1ker84/destroying_performance_with_strictness/ 5. http://www.reddit.com/r/haskell/comments/1ka4q6/a_great_series_of_posts_on_the_power_of_monoids/ 6. http://www.reddit.com/r/haskell/comments/1ka4q6/a_great_series_of_posts_on_the_power_of_monoids/ 7. https://www.fpcomplete.com/user/edwardk/cellular-automata 8.
Re: [Haskell-cafe] Yet Another Forkable Class
Perhaps effect libraries (there are several to choose from) could be a better answer to Fork effects than monad transformers. One lesson from the recent research in effects is that we should start thinking what effect we want to achieve rather than which monad transformer to use. Using ReaderT or StateT or something else is an implementation detail. Once we know what effect to achieve we can write a handler, or interpreter, to implement the desired operation on the World, obeying the desired equations. And we are done. For example, with ExtEff library with which I'm more familiar, the Fork effect would take as an argument a computation that cannot throw any requests. That means that the parent has to provide interpreters for all child effects. It becomes trivially to implement: Another example would be a child that should not be able to throw errors as opposed to the parent thread. It is possible to specify which errors will be allowed for the child thread (the ones that the parent will be willing to reflect and interpret). The rest of errors will be statically prohibited then. instance (Protocol p) = Forkable (WebSockets p) (ReaderT (Sink p) IO) where fork (ReaderT f) = liftIO . forkIO . f = getSink This is a good illustration of too much implementation detail. Why do we need to know of (Sink p) as a Reader layer? Would it be clearer to define an Effect of sending to the socket? Computation's type will make it patent the computation is sending to the socket. The parent thread, before forking, has to provide a handler for that effect (and the handler will probably need a socket). Defining a new class for each effect is possible but not needed at all. With monad transformers, a class per effect is meant to hide the ordering of transformer layers in a monad transformer stack. Effect libraries abstract over the implementation details out of the box. Crutches -- extra classes -- are unnecessary. We can start by writing handlers on a case-by-case basis. Generalization, if any, we'll be easier to see. From my experience, generalizing from concrete cases is easier than trying to write a (too) general code at the outset. Way too often, as I read and saw, code that is meant to be reusable ends up hardly usable. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Retrieving Haddock comments with haskell-src-exts
Niklas Broberg niklas.broberg at gmail.com writes: Hmm. I see the difficulty here, ... On Wed, Aug 14, 2013 at 8:57 PM, Mateusz Kowalczyk wrote: ... The main problem with this approach is that we get comments (and their SrcLoc) as a separate list. Hi Niklas, Mateusz, It seems that haskell-src-exts has done quite a lot of the hard work (impressive!). Function parseFileWithComments returns the AST annotated with SrcLoc for each major node, and with a separate list of comments annotated with SrcSpan. So it should be possible to reconstitute the source and intersperse the comments between the nodes(?) -- or detect where a comment spans code. (I'm also looking at the discussion about comments on Niklas's announcement of 1.14.0 ) Could there be a style of prettyPrint that carries the list of comments (as a continuation) alongside walking the AST, and consumes/outputs each comment where the comment's Span falls between the nodes' Loc? Would this need too much lookahead? (And thank you to Adam for introducing me to the joys of source-munging. http://www.haskell.org/pipermail/haskell-cafe/2013-August/108426.html .) AntC ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
