Re: [Haskell-cafe] Proposal: new function for lifting
this is a funny trick, and it looks saner than the more general $ * combinators. i see many situations where i could use that to lift my own combinators, or to replace the backticks (``) to lift the infix function. thx - marc Gesendet: Freitag, 27. September 2013 um 21:51 Uhr Von: Thiago Negri evoh...@gmail.com An: Haskell-Cafe haskell-cafe@haskell.org Betreff: [Haskell-cafe] Proposal: new function for lifting Everybody is claiming that using lift is a bad thing. So, I come to remedy this problem. Stop lifting, start using shinny operators like this one: (^$) :: Monad m = m a - (a - b - c) - m b - m c (^$) = flip liftM2 Then you can do wonderful stuff and you will never read the four-letter word in your code again: \ Just 42 ^$(+)$ Nothing Nothing \ Just 10 ^$(+)$ Just 20 Just 30 \ let add = (+) \ Just 30 ^$ add $ Just 12 Just 42 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Alternative name for return
very insightful, thx Jerzy. imho, this is a good reason not to use already known words like lift,return,inject,pure etc. while still using the word Monad. (this is something that bothered me for years.) no one -of those who say no one- does understand Monads because it does not explain itself nor suggest its utility, while the other words probably tend to cause a very false sense of understanding. so, long talk few suggestions if it should be about Monads as a concept, i'd suggest 1) unit and counit for Monads and Comonads. (this is my personal favorite choice, probably because i did learn to understand Monads by reading a paper about Comonads.) if it should be more selfexplaining for the average coder, then 2) let,set,put,be,:= or return allowed only at end of script - use let anywhere else for ScriptLike (aka Monad) as a strict version of return, i'd suggest something that may somehow fit into 1 and 2: 3) eval = Control.Exception.evaluate :: a - IO a regards - marc Gesendet: Dienstag, 06. August 2013 um 11:43 Uhr Von: Jerzy Karczmarczuk jerzy.karczmarc...@unicaen.fr An: haskell-cafe@haskell.org Betreff: Re: [Haskell-cafe] Alternative name for return Le 06/08/2013 11:01, J. Stutterheim a écrit : ... So in reply to Jerzy, I do want to encourage the discussion in the Noble Domain of Philosophy and I also want to repeat that I am not proposing to change Haskell or Haskell libraries Jurriën, I taught Haskell for several years. I saw the disgraceful confusion in heads of my students whose previous programming experience was based on Python, and who learned Haskell and Java in parallel. So, I won't claim that names are irrelevant. And return in particular. However, my personal philosophy is the following: accept the fact that words in one language -- formal or natural -- mean something different than in another one. [[In French the word file in computerese is queue in English; this is in fact a French word meaning tail in English, and I have several dozens of such examples... And so what?...]] It is good to choose consciously some good names while elaborating a standard. But getting back to it after several years, is -- for me -- a waste of time. This, unfortunately, pollutes the true philosophy as well. I believe that at least 80% of the progress in the philosophy of religions belongs to the linguistic domain. The anglosaxons corupted the word semantics, used in a pejorative sense: discussion about superficialities, the words, not the concepts, while the true semantics is about the true sense. So, sorry for being sarcastic, or even cynical in my previous post, but I sincerely think that oldies are oldies, let them be, and work more on issues that are still evolving. All the best. Jerzy ___ 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] Spam on list??
i get this spam whenever anyone sends a mail to @eukor.com and this list at the same time. i think that this kind of spam-bot sends to all recipients, not only to the person who sent it; but sends only if it sees @eukor.com in the TO: or CC: field. so, if anyone knows a similar unsafeSpamBlocker, anyone of us might be able to disable one or both bots simply by sending a funny email (from a throw-away account because of side effects!!) to both email adresses - each twice to make it exponential. that would be the easiest pragmatic solution. sadly, i don't know any other unsafeSpamBlocker than this; it is years ago that i saw one. i guess they do not survive more than a few weeks – at least not without beeing blacklisted automatically. - marc Gesendet: Montag, 01. Juli 2013 um 17:30 Uhr Von: Brandon Allbery allber...@gmail.com An: vlatko.ba...@gmail.com Cc: Haskell-Cafe haskell-cafe@haskell.org Betreff: Re: [Haskell-cafe] Spam on list?? On Mon, Jul 1, 2013 at 11:19 AM, Vlatko Basic vlatko.ba...@gmail.com[vlatko.ba...@gmail.com] wrote: Anybody else getting this spam emails from j...@eukor.com[j...@eukor.com] every time a message is sent to Cafe? Yes, and I'm hoping a list admin steps in soon. The irony is, it's their *anti*spam filter. They decided to use one of those obnoxious whitelisting systems that requires all senders to register with it before it will pass on their mail... but didn't exclude mailing lists from this. Mailing lists, of course, can't authenticate, so they're sending all these image-heavy please whitelist yourself messages in Korean to the list submission address *and* not seeing any actual list traffic. This is one of the reasons I sometimes wish that use of an active spam whitelist like this were grounds for disabling the user's email account. They can't even tell what kind of mess they're making. -- brandon s allbery kf8nh sine nomine associates allber...@gmail.com[allber...@gmail.com] ballb...@sinenomine.net[ballb...@sinenomine.net] unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net[http://sinenomine.net] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Optimal line length for haskell
O_o Those are damn strange reasons to restrict oneself to 80 chars, iMho. I tend to look at ONE file at a time, on one fullscreen widescreen. 100 chars per line is more or less normal; I have my vertical line limit marker set to 100, but only for layout-zen. My lines have sometimes 200 chars length, which causes the less important (long) code not to clutter my overview on the 50 neighbouring lines (~10 functions overview on the left half of the screen). Otherwise, I'd use a browser/Haddock on one part of the screen just to see an overview of the code I'm writing. I'm now wondering, whether this could have sth to do with my ADD, which I had the first 3 decades of my life (and without whiteboard). I think, I should try to code in a small narrow window of 1/4 of my screen, just to test whether that would (still) be a handicap. Roman: academic background... Funny; my impression about this matter was from the other point of view: Short lines are good for diff/patch files. Are there more people here with ADD (or ADD-history) and long-lines-disorder? Or is that just me? - marc Original-Nachricht Datum: Mon, 29 Oct 2012 11:32:29 -0400 Von: MightyByte mightyb...@gmail.com An: Jake McArthur jake.mcart...@gmail.com CC: Haskell Cafe haskell-cafe@haskell.org Betreff: Re: [Haskell-cafe] Optimal line length for haskell I also stick to a pretty rigid 78 characters. Doing so actually helps me fit more code onto my screen at a time because I usually have two or three columns of open files side by side. I find that I need this more often than I need to see a single function on a page (thanks to Haskell's traditionally small functions). But this works for single functions as well because I can open the same file in multiple columns at different locations in the file. The ideal line length for text layout is based on the physiology of the human eye… At normal reading distance the arc of the visual field is only a few inches – about the width of a well-designed column of text, or about 12 words per line. Research shows that reading slows and retention rates fall as line length begins to exceed the ideal width, because the reader then needs to use the muscles of the eye and neck to track from the end of one line to the beginning of the next line. If the eye must traverse great distances on the page, the reader is easily lost and must hunt for the beginning of the next line. Quantitative studies show that moderate line lengths significantly increase the legibility of text. Web Style Guide – Basic Design Principles for Creating Website Patrick J. Lynch and Sarah Horton 2nd edition, page 97. On Mon, Oct 29, 2012 at 10:37 AM, Jake McArthur jake.mcart...@gmail.com wrote: I stick to 80 columns fairly rigidly. This is not only so that it fits into narrow windows, but also so that any two subexpressions in the same expression tend to be close together on my screen, which makes it easier for me to reason about it. If only it was easy for me to read and write code on a Hilbert curve... :) I don't think long lines indicate a design problem; it's solely a formatting thing. On Mon, Oct 29, 2012 at 7:50 AM, Rustom Mody rustompm...@gmail.com wrote: There was a recent discussion on the python list regarding maximum line length. It occured to me that beautiful haskell programs tend to be plump (ie have long lines) compared to other languages whose programs are 'skinnier'. My thoughts on this are at http://blog.languager.org/2012/10/layout-imperative-in-functional.html. Are there more striking examples than the lexer from the standard prelude? [Or any other thoughts/opinions :-) ] Thanks, Rusi ___ 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 -- () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments (in deutsch: http://www.gerstbach.at/2004/ascii/) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [Haskell] mapM with Traversables
Hi Thomas, this should be on the haskell-cafe or haskell-beginners mailing list. Haskell@... is mainly for announcements. You have: f :: Monad m = a - m b Data.Traversable.mapM :: (Monad m, Traversable t) = (a - m b) - t a - m (t b) So, if you define g with g a = do Data.Traversable.mapM f a or in short g = Data.Traversable.mapM f , then the type will be g :: (Monad m, Traversable t) = t a - m (t b) instead of g :: [a] - m (Seq b) . Try using ghci to find these things out. It helps to get not confused with the types. Besides the missing Monad context, g misses a generic way to convert between different Traversables, which does not exist. You can only convert from any Traversable (imagine a Tree) toList; not all Traversables have a fromList function. For conversion, you might want to use Foldable and Monoid, fold to untangle and mappend to recombine; but any specific fromList function will surely be more efficient. Regards - Marc Original-Nachricht Datum: Wed, 28 Sep 2011 17:27:58 -0600 Von: thomas burt thedwa...@gmail.com An: hask...@haskell.org Betreff: [Haskell] mapM with Traversables Hi - I have a function, f :: Monad m = a - m b, as well as a list of a's. I'd like to produce a sequence (Data.Sequence) of b's, given the a's: g :: [a] - m (Seq b) g a = do Data.Traversable.mapM f a -- type error! I see that Data.Traversable.mapM f a doesn't work... is this like asking the compiler to infer the cons/append operation from the type signature of g? Do I need to write my own function that explicitly calls the append functions from Data.Sequence or can I do something else that would work for any g :: Traversable t, Traversable u = t a - m (u b) given f :: a - m b? Thanks for any comments! Thomas ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Endian conversion
you are right, that pice of code is ugly. i would write sth simmilar (Int32-[Word8]) like you did, iff it should be able to cross-compile or do not need to be fast or should not need TH. well, i think, in the case of joel's project the last sentence means ..., iff true or true or undefined. is there any architecture with sth like 0xaabbccdd-bb aa dd cc, ghc (or any other haskell-compiler) runs on? (i did know, that such architectures exist.) - marc Udo Stenzel wrote: Why don't you pull out 4 bytes and assemble them manually? To that I'd like to add a snippet from NewBinary itself: | instance Binary Word32 where | put_ h w = do | putByte h (fromIntegral (w `shiftR` 24)) | putByte h (fromIntegral ((w `shiftR` 16) .. 0xff)) | putByte h (fromIntegral ((w `shiftR` 8) .. 0xff)) | putByte h (fromIntegral (w .. 0xff)) | get h = do | w1 - getWord8 h | w2 - getWord8 h | w3 - getWord8 h | w4 - getWord8 h | return $! ((fromIntegral w1 `shiftL` 24) .|. |(fromIntegral w2 `shiftL` 16) .|. |(fromIntegral w3 `shiftL` 8) .|. |(fromIntegral w4)) This obviously writes a Word32 in big endian format, also known as network byte order, and doesn't care how the host platform stores integers. No need for `hton' and `ntoh'. To convert it to write little endian, just copy it and reorder some lines. (But I think, writing LE integers with no good reason and without an enclosing protocol that explicitly declares them (like IIOP) is a bad idea.) [Which reminds me, has anyone ever tried implementing a Corba ORB in Haskell? There's a binding to MICO, but that just adds to the uglyness of MICO and does Haskell a bit of injustice...] Well, I liked that bit of Template Haskell code that Marc sent. I'm now stuck trying to adapt it to read Storables :-). I don't. It's complex machinery, it's ugly, it solves a problem that doesn't even exist and it solves it incompletely. It will determine the byte order of the host system, not of the target, which fails when cross-compiling, and it doesn't work on machines with little endian words and big endian long words (yes, this has been seen in the wild, though might be extinct these days). Use it only if You Know What You Are Doing, have a performance problem and also know that writing integers en bloc would help with it. I could read a FastString from a socket since it has IO methods but I don't know how to convert the FS into a pointer suitable for Storable. So much to learn :-). useAsCString might be your friend. But so might be (fold (:) []). Udo. -- The greatest dangers to liberty lurk in insidious encroachment by men of zeal, well-meaning but without understanding. -- Brandeis ___ 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] Endian conversion
well, fastest conversion to compute could be an assembler-command, but if we don't use that, it could be converted via Foreign.Storable and sth like the following: (i did not test it, and i hope, TH works like this...) data (Integral a) = BigEndian a = BigEndian a deriving (Eq,Ord,Enum,...) be = $( (1::CChar)/=(unsafePerformIO $ with (1::CInt) $ peekByteOff `flip` 0) ) :: Bool instance (Storable a) = Storable (BigEndian a) where sizeOf (BigEndian a) = sizeOf a alignment (BigEndian a) = alignment a peek = if be then peek0 else peekR where peek0 (BigEndian a) = peek a peekR = peekByteOff `flip` 0 peekByteOff = if be then peekByteOff0 else peekByteOffR where peekByteOff0 (BigEndian a) = peekByteOff a peekByteOffR (BigEndian a) i = peekByteOff a (sizeOf a - 1 - i) ...poke... - marc Tomasz Zielonka wrote: On 10/3/05, Joel Reymont [EMAIL PROTECTED] wrote: Folks, Are there any endian conversion routines for Haskell? I'm looking to build binary packets on top of NewBinary.Binary but my data is coming in little-endian whereas I'll need to send it out big endian. From your question I assume you want functions like htonl / ntohl. I think the cleanest approach is to always have yours Ints, etc in host order, and place the endianness stuff in serialization / deserialization code, ie. on the Number - Byte sequence boundary. Having htonl/ntohl as pure functions in Haskell would be a bit ugly, because they would be defined differently on different platforms, and putting them in the IO monad would make them barely usable. Best regards Tomasz ___ 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] Endian conversion
for just making IO and a little bit-conversion, i would use c++ or even c. for such a problem you have to be near the machine, not necessarily near mathematical abstraction. there exist assembler-commands to flip endians of register-values, so i would just search in /usr/include/*/* for a platform independent c-function, and either pipe a proxy through such a little prog, or patch an existing proxy, like tinyproxy. of course, if you want to make more than just a proxy, or if you want to play with different languages, be welcome to use haskell. but remind, it is not easy to use high-developed-mars-rover-technology to replace a shovel for playing with sand at the beach. - marc Joel Reymont wrote: Well, I'm looking for suggestions on how to implement this. I'll basically get a chunk of data from the socket that will have things little-endian and will need to send out a chunk that will have the numbers big-endian. This is a proxy server that does binary protocol conversion. It's a breeze to implement in Erlang but I'm partial to Haskell and trying to apply it to all sorts of problems. Please, let me know if this is not the type of problem to apply Haskell to ;-). Thanks, Joel On Oct 3, 2005, at 8:35 AM, Tomasz Zielonka wrote: Having htonl/ntohl as pure functions in Haskell would be a bit ugly, because they would be defined differently on different platforms, and putting them in the IO monad would make them barely usable. -- http://wagerlabs.com/idealab ___ 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] Endian conversion
nice project. (except that winonly-closedsource-thing. my condolence.) on which platform are you programming? mac? linux-ppc? i see that you understood most of that code. big-endian-test: the number 1234 has two ends (like a sausage), the end with the 1 is the big end (1000), the 4 is the little one. if you save he number 1 as int in little endian, then you write the bytes 01 00 00 00, and in big endian it is 00 00 00 01. so, if you read the first char, then it will either be ==1 (little) or /=1 (big). to write that LittleEndian stuff, you only need to replace Big with Little and if be then with if not be then. it is the question wether to use he function xyz0(derived) or xyzR(reverse order of bytes). i hope, that the compiler optimizes if True away. to use the Storables, read the docu about the libs(functions) Network.Socket(sendBufTo) Foreign.Marshal.Utils(with) Foreign.Storable(peekThis,peekThat) you just need to read LittleEndian CInt, remove that LittleEndian-constructor, work with that CInt, put the BigEndian-constructor at that CInt, write it... maybe you need to convert LE and BE enums, too. use (toEnum . fromEnum) to convert between any enum and CInt. good n8. - marc Joel Reymont wrote: Well, I liked that bit of Template Haskell code that Marc sent. I'm now stuck trying to adapt it to read Storables :-). It seems, on a second glance, that there's not that much to adapt. If I read Marc's code correctly it derives Storable and uses the peek, etc. methods to swap bytes around. Which means to me that so long as the byte swapping methods are implemented and I try to store a BigEndian or LittleEndian it would be stored correctly for me. Is this so? To recap, I'm trying to read binary packets from a socket and the first thing I do is read the packet length. I then need to read the packet body where the numbers are little or big endian. After processing the packet I need to write it out and the numbers again could be little or big endian. I could read a FastString from a socket since it has IO methods but I don't know how to convert the FS into a pointer suitable for Storable. So much to learn :-). Thanks, Joel On Oct 3, 2005, at 9:33 PM, Udo Stenzel wrote: Why don't you pull out 4 bytes and assemble them manually? Three shifts, logical ors and fromIntegrals aren't that much of a burden after all. -- http://wagerlabs.com/idealab ___ 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] Basic type classing question.
maybe, i completely missunderstand you. please, could you program your example in another language than haskell, one you know better? i'm not sure -- did you try to define variables instead of types? data Employee = Emp data Department = Dept translated to c++ this means sth like typedef void Employee; typedef void Department; did you want sth like ...? data Employee = Emp [(String,Either String Int)] emp1 :: Employee emp1=Emp [(Name,Left Karl Ranseier),(Identifier,Right 7),(Address,Left Graveyard 13)] -marc Karl Grapone wrote: Hi, I've just started learning Haskell, and I must admit I'm finding it a bit hard to get my head around the typing system... If I wanted to represent Employees and Departments in a Haskell program I could use data declarations like so: data Employee = Emp ... data Department = Dept ... This seems limited in (at least) two ways: I can't dynamically add fields to an employee or department, and once I pull a field out of an instance I lose type information. What I want to be able to do is add and remove fields while the system is running, I suppose via hs-plugins, and I should be prevented from, for example, accidentally taking an employees first name and using it as a departments address. My first attempt was the following, which isn't even valid and doesn't appear to buy me much anyway. class DataContainer c class DataContainer c = DataField f c a where extract :: f - a apply :: (a - a - a) - f - f - f data DataContainer c = Field c a = Fld c a instance DataField Field c a where extract (Fld _ a) = a apply f (Fld c a1) (Fld _ a2) = Fld c (f a1 a2) data Employee = Emp instance DataContainer Employee data Department = Dept instance DataContainer Department type EmployeeName = Field Employee String type EmployeeAddress = Field Employee String type EmployeeIdentifier = Field Employee Integer type DepartmentAddress = Field Department String type DepartmentIdentifier = Field Department Integer ... The 'DataField instance Field' declaration gives kind errors regarding how many type arguments Field is applied to. I don't claim to understand kinds at this point. Even if it did work, apply doesn't appear to force the arguments to be of the same type, and the declared type synonyms aren't enough to prevent me getting employee names and addresses confused. Is there a correct way to express what I'm trying to do? Or is it a bad idea to start with? Thanks Karl ___ 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] Newbie syntax question
map (foo 5) my_list_of_lists_of_doubles 1. map (flip foo 5) my_list_of_lists_of_doubles 2. map (`foo` 5) my_list_of_lists_of_doubles 3. map (\x-foo x 5) my_list_of_lists_of_doubles 4. [foo x 5 | x - my_list_of_lists_of_doubles] well, i've followed this discussion a while, but i did not see that solution i used for years. (i like solution 2, never thought of it before.) my solution is a variant of 1, that makes the reading a little bit easier -- at least to me. 5. map (foo `flip` 5) my_list_of_lists_of_doubles the `flip` shows the position behind foo, where to put the parameter. its a pitty that it only works if there is only one parameter behind `flip`. so, with abcd :: a-b-c-d-x abcd a b `flip` d :: c-x works, but abcd a `flip` c d :: b-x does not. experimenting with Data.Arrow, it could look like: (abcd a ($ c) ($ d)) :: b-x or with a flip-arrow combination: (abcd a `flip` c) ($ d) :: b-x so, instead of hacking with arrows on it, i prefer solutions 3 and 4 whenever 5 does not work. - marc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
