Re: [Haskell-cafe] I love purity, but it's killing me.
Hello Tom, Friday, February 8, 2008, 9:33:35 AM, you wrote: The process of converting an expression tree to a graph uses either Eq or Ord (either derived or a custom instance) to search and build a set of unique nodes to be ordered for execution. in similar situation, i've added hash field to each node, initialized by smart constructor: data Expression = Add Hash Expression Expression | ... type Hash=Int add x y = Add (x*y+1234567) x y ... -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I love purity, but it's killing me.
On Fri, 8 Feb 2008, Tom Hawkins wrote: I've been programming with Haskell for a few years and love it. One of my favorite applications of Haskell is using for domain specific languages. However, after designing a handful of DSLs, I continue to hit what appears to be a fundamental hurdle -- or at least I have yet to find an adequate solution. It seems to become a FAQ. I think all DSLs suffer from the same problems: sharing and recursion. I've used wrappers for CSound, SuperCollider, MetaPost, they all have these problems. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] FP and Quality
On 07/02/2008, Benjamin L. Russell [EMAIL PROTECTED] wrote: - text follows immediately after this line - Haskell vs. Ada vs. C++ vs. Awk vs. ... An Experiment in Software Prototyping Productivity (1994), by Paul Hudak and Mark P. Jones: http://citeseer.ist.psu.edu/41732.html This one's quite interesting but refers to the much longer report. In the bibliography it is listed as unpublished, but during the text the authors suggest you read it anyway. Does anyone have a source for this document. (A quick search has only produced further citations in other places.) J.A.N. Lee, B. Blum, P. Kanellakis, H. Crisp, and J.A. Caruso. ProtoTech HiPer-D Joint Prototyping Demonstration Project, February 1994. Unpublished; 400 pages. Cheers, D -- Dougal Stanton [EMAIL PROTECTED] // http://www.dougalstanton.net ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I love purity, but it's killing me.
Hi, (Warning: longish message!) There is some concern, and rightly so, that observable sharing is dangerous, and that your Haskell program will explode if you use it, and perhaps even that anyone who uses it is dirty and should be sent to matron's for a good scrubbing! However, when used safely, it is not a hack, nor even dirty, but a nice, simple solution to an otherwise nasty problem. Below I define what I mean by safely. First consider the circumstances under which obserevable sharing is useful. Typically we have some Haskell function f that produces a symbolic representation of an expression. For whatever reason, we'd like to *generate a program* that computes the value of this expression, rather that computing it in Haskell. For example, in Lava, we want to generate a VHDL program so that the expression can be computed on, say, an FPGA. In Tom's case, he wants to generate a C program to compute the expression. All perfectly reasonable, and in my opinion, a very powerfull way to use Haskell. Now recall that referential transparency lets you replace equals with equals without changing the *value produced* by a program. Note that it says nothing about preserving *runtime behaviour*. Sharing, for example, may be lost. So if you do equational reasoning on function f (above), and loose some sharing, then you can only expect that the same sharing will also be also lost in the generated program. As long as the generated program computes the same result as it did before, referential transparency will be, overall, preserved; it would only be lost intermediately. This is what I mean by safe. Now, there remains the concern that Haskell's semantics does not enforce sharing. A Haskell compiler is free to change the sharing a program at a whim, unknowingly to the programmer who may be relying on it in for an efficient program. However, to my knowledge, it is an unwritten rule of Haskell compilers that sharing *is* preserved, and that they do perform *graph* reduction. Clean, a similar language to Haskell, indeed has a semantics based on graphs. So I don't believe Haskell being non-strict (not necessarily lazy) is a good reason for not using observable sharing. Though I do feel better when I compile without -O. :-) Finally, when I say observable sharing, I don't necessarily mean it as defined by Koen Claessen and David Sands. I simply mean the use of unsafePerformIO to detect sharing, whether or not this is done by an eq predicate on Refs. (I say this because I think there are simpler ways to detect sharing, though these will probably not have the nice semantic properties of observable sharing.) Sorry for the somewhat long exposition. :-) Matt. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Draft chapters of Real World Haskell now publicly available
Am Donnerstag, 7. Februar 2008 18:33 schrieben Sie: Interesting. Thanks for the reply. It might be nice to have some performance benchmarks for all these experimental systems, so we can compare them. I think, the most important thing is the asymptotical time behavior, e.g., whether the time of a certain task is linear, logarithmic or constant in the number of widgets. Constant factors can always be improved. So performance benchmarks don’t seem so important to me in the current early state of FRP GUI libraries. I could understand that performance might be an issue for games, but for GUIs? I mean many imperative GUI systems use rather slow message dispatching systems, and we use those every day. Look at the new Windows Presentation Foundation system found in VISTA. Here events are broadcasted and routed through the whole element tree. This is also rather slow I guess. Are they rooted through every node of the tree (linear time) or are they routed down the tree to a leaf (not more than logarithmic time, probably). The latter would be acceptable, the former not. The problem I noted on the Grapefruit talk page might result in a Yampa-based GUI taking linear time for handling a single event (but I’m not completely sure about that). Does Vista’s event handling really have linear behavior as your statement seems to suggest? Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: threads + IORefs = Segmentation fault?
David Roundy wrote:
I'm working on some new progress-reporting code for darcs, and am getting
segmentation faults! :( The code uses threads + an IORef global variable
to do this (with lots of unsafePerformIO). So my question for the gurus
who know more about this than I do: is this safe? I thought it would be,
because only one thread ever modifies the IORef, and the others only read
it. I don't really care if they read a correct value, as long as they
don't segfault.
The code (to summarize) looks like:
{-# NOINLINE _progressData #-}
_progressData :: IORef (Map String ProgressData)
_progressData = unsafePerformIO $ newIORef empty
updateProgressData :: String - (ProgressData - ProgressData) - IO ()
updateProgressData k f = when (progressMode) $ modifyIORef _progressData
(adjust f k)
setProgressData :: String - ProgressData - IO ()
setProgressData k p = when (progressMode) $ modifyIORef _progressData (insert k
p)
getProgressData :: String - IO (Maybe ProgressData)
getProgressData k = if progressMode then lookup k `fmap` readIORef _progressData
else return Nothing
(I'm a bit behind with haskell-cafe, sorry for not seeing this sooner...)
Yes, that should all be fine, because the IORef is only modified from one
thread, and read from the other(s). If you were modifying the IORef from
more than one thread you would need to use atomicallyModifyIORef, or MVars.
Cheers,
Simon
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Re: [Haskell-cafe] Best practice for embedding files in a GHC-compiled tool?
Op 7-feb-2008, om 13:53 heeft Dave Bayer het volgende geschreven: Under this extreme hypothesis, how do I embed a compressed tar file into a single file command line tool written in Haskell and compiled by GHC? Hack up a shell script or a small Haskell program to automatically generate a Haskell file of the form: module TarFile where import Data.ByteString as B myTarFile = B.pack [tar file as list of Word8s here] You could also do that using Template Haskell, as you already hinted, but this sounds less like rocket science :-) Reinier ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question concerning ANSI void *
On Feb 8, 2008 9:13 AM, Galchin Vasili [EMAIL PROTECTED] wrote: Let's take a concrete but made up case .. suppose we want to call through to pthread_create and pass the (void *) argument to pthread_create which in turn gets interpreted by the pthread that is launched. How would one populate the C struct that is passed to the launched pthread keeping in mind that this C struct is variable in length? From the FFI how would one model this C struct? It tough to be helpful with such a generic request. Here are some options that you can consider: 1) Write a wrapper function in C which has a nicer FFI interface to call from Haskell. Using cabal this is pretty painless and, if the interface suits it, it probably the easiest solution. 2) Call pthread_create directly with the FFI. You can give the FFI function a Haskell type with 'Ptr ()' or 'Ptr X', it doesn't really matter. However the type system serves you best, do it that way. This means that you need to populate the struct yourself in Haskell. The issue with this is that the local system defines lots of things like padding and alignment which mean that the layout of the structure in memory is complex and platform specific. Tools like hsc2hs[1] or c2hs will be very helpful here. Dealing with the variable length probably isn't an issue. Usually variable length structures have a fixed header and a variable tail, where the tail is an array of primitives. You can malloc the correct sized region, use one of the previous tools to fill in the fixed header and then use poke to complete the tail. I might be able to be more helpful if you give the actual struct and function prototype that you're trying to wrap. Cheers [1] http://therning.org/magnus/archives/tag/hsc2hs [2] http://www.cse.unsw.edu.au/~chak/haskell/c2hs/ -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org 650-283-9641 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question concerning ANSI void *
Let's take a concrete but made up case .. suppose we want to call through
to pthread_create and pass the (void *) argument to pthread_create which in
turn gets interpreted by the pthread that is launched. How would one
populate the C struct that is passed to the launched pthread keeping in mind
that this C struct is variable in length? From the FFI how would one model
this C struct?
Thanks, Vasili
On 2/7/08, Adam Langley [EMAIL PROTECTED] wrote:
2008/2/7 Galchin Vasili [EMAIL PROTECTED]:
Ok .. I am writing a Haskell function that will call down into the
ANSI
C library .. blah :: - Ptr Word8 - The underlying C
function
that blah is calling has a void * so I am using Ptr Word 8 to
model
the void *.
Depending on the context, void * is generally either taken as a Ptr
() (for an opaque pointer) or Ptr Word8 (for calls like memcpy).
I propose to have the callers of function blah to populate a
data structure something like Ptr Buz where data Buz = { }
and
then do a recast :: Ptr Word 8 - Ptr Buz when invoking function
blah.
Does this seem reasonable? Is there a better way?
Generally, Ptr x is only used where x is either a shadow type or a
Bits type. Having a Ptr Baz where Baz is an ADT seems a little odd. If
you need to translate a structure from Haskell to C code, probably you
are better off having callers pass in a Baz then, internal to the
wrapping, fill out the C structure and call the FFI function with a
Ptr CBaz (where CBaz is a shadow type).
AGL
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Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
Am Donnerstag, 7. Februar 2008 16:31 schrieben Sie: On Feb 7, 2008 4:16 PM, Wolfgang Jeltsch [EMAIL PROTECTED] wrote: […] You seem to write 12 as 1 :+ 2 instead of () :+ 1 :+ 2. But I think, the latter representation should probably be prefered. With it, :+ always has a number as its left argument and a digit as its right. Without the () :+ we get ugly exceptional cases. You can see this, for example, in the instance declarations for Compare. With the second representation, we could reduce the number of instances dramatically. We would define a comparison of digits (verbose) and than a comparison of numbers based on the digit comparison (not verbose). Even if () would be preferred from the programmers point of view (I'm not sure how much we could reduce the number of instances though), it makes the representation less attractive on the user-side. Anyone using the library would find it annoying and would wonder why is it neccessary. I wouldn’t wonder. Leaving out the () :* part just works because our type-level “values” are not typed, i.e., there aren’t different kinds Digit and Number but only kind *. If :+ would be a data constructor (on the value level), it would take a number and a digit argument which would forbid using a digit as its left argument. So I consider using a digit on the left as “unclean”. It’s similar to using a number as the second part of a cons cell in LISP. […] Best wishes, Wolfgang ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
On Feb 8, 2008, at 11:14 , Stefan Monnier wrote: You seem to write 12 as 1 :+ 2 instead of () :+ 1 :+ 2. But I think, the latter representation should probably be prefered. (...) How 'bout treating :+ as similar to `append' rather than similar to `cons'? Basically treat :+ as taking 2 numbers (rather than a number and a digit). Dumb questions department: why not define e.g. D'0 .. D'9 as () :* 0 .. () :* 9? Programmers then get D'1 :* 2, but the library sees () :* 1 :* 2. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question concerning ANSI void *
a couple of concrete examples:
typedef struct {char a; int b; char str[8]} type1;
typedef struct {long c; char d} type2;
So to pthread_create (just an example function) we could be passing a struct
of type1 or a struct of type2 .. i.e. arbitrary length and content ... I am
trying to better understand this. I see some of the poke functions mentioned
in the FFI. Which one are you alluding to?
Regards, Vasili
On 2/8/08, Adam Langley [EMAIL PROTECTED] wrote:
On Feb 8, 2008 9:13 AM, Galchin Vasili [EMAIL PROTECTED] wrote:
Let's take a concrete but made up case .. suppose we want to call
through
to pthread_create and pass the (void *) argument to pthread_create which
in
turn gets interpreted by the pthread that is launched. How would one
populate the C struct that is passed to the launched pthread keeping in
mind
that this C struct is variable in length? From the FFI how would one
model
this C struct?
It tough to be helpful with such a generic request. Here are some
options that you can consider:
1) Write a wrapper function in C which has a nicer FFI interface to
call from Haskell. Using cabal this is pretty painless and, if the
interface suits it, it probably the easiest solution.
2) Call pthread_create directly with the FFI. You can give the FFI
function a Haskell type with 'Ptr ()' or 'Ptr X', it doesn't really
matter. However the type system serves you best, do it that way. This
means that you need to populate the struct yourself in Haskell. The
issue with this is that the local system defines lots of things like
padding and alignment which mean that the layout of the structure in
memory is complex and platform specific. Tools like hsc2hs[1] or c2hs
will be very helpful here. Dealing with the variable length probably
isn't an issue. Usually variable length structures have a fixed header
and a variable tail, where the tail is an array of primitives. You can
malloc the correct sized region, use one of the previous tools to fill
in the fixed header and then use poke to complete the tail.
I might be able to be more helpful if you give the actual struct and
function prototype that you're trying to wrap.
Cheers
[1] http://therning.org/magnus/archives/tag/hsc2hs
[2] http://www.cse.unsw.edu.au/~chak/haskell/c2hs/
--
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http://www.imperialviolet.org 650-283-9641
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Re: [Haskell-cafe] User groups meeting all over the world
Hi Neil, London HUG is not on the list because we're not meeting in the next two weeks. Rest assured we are on the wiki page though. On that note, I am looking again for topics and speaker for the next full meeting at City University. It will likely be in the middle of March. If anybody has ideas for talks, please let me know. Also talk to me if there is something in particular you would like to *hear* about... then we'll do our best to find somebody who can talk about it. Thanks, Another Neil On 2/8/08, Neil Mitchell [EMAIL PROTECTED] wrote: Hi Fun in the afternoonLondon/UKFebruary 12 Fun in the afternoon is great, but its not really a user group - it is still primarily an academic event, although is open to everyone. There is LUG, which is the London Haskell Users Group, which should definately be on this list. Thanks Neil ___ 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] :i and :t give different types
On Feb 8, 2008 9:55 AM, Simon Peyton-Jones [EMAIL PROTECTED] wrote: I have not been following closely but if Don thinks there's a bug there probably is. Can someone submit a bug report pls? Better still a patch! :-) Simon Ok, I filed a bug report. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question concerning ANSI void *
basically I am trying to implement ioctl for the Posix library .. so a
possible signtaure would be:
fdIoctl :: Fd - Int - Ptr Word 8 - IO( Ptr Word8)
Vasili
On 2/8/08, Galchin Vasili [EMAIL PROTECTED] wrote:
a couple of concrete examples:
typedef struct {char a; int b; char str[8]} type1;
typedef struct {long c; char d} type2;
So to pthread_create (just an example function) we could be passing a
struct of type1 or a struct of type2 .. i.e. arbitrary length and content
... I am trying to better understand this. I see some of the poke functions
mentioned in the FFI. Which one are you alluding to?
Regards, Vasili
On 2/8/08, Adam Langley [EMAIL PROTECTED] wrote:
On Feb 8, 2008 9:13 AM, Galchin Vasili [EMAIL PROTECTED] wrote:
Let's take a concrete but made up case .. suppose we want to call
through
to pthread_create and pass the (void *) argument to pthread_create
which in
turn gets interpreted by the pthread that is launched. How would one
populate the C struct that is passed to the launched pthread keeping
in mind
that this C struct is variable in length? From the FFI how would one
model
this C struct?
It tough to be helpful with such a generic request. Here are some
options that you can consider:
1) Write a wrapper function in C which has a nicer FFI interface to
call from Haskell. Using cabal this is pretty painless and, if the
interface suits it, it probably the easiest solution.
2) Call pthread_create directly with the FFI. You can give the FFI
function a Haskell type with 'Ptr ()' or 'Ptr X', it doesn't really
matter. However the type system serves you best, do it that way. This
means that you need to populate the struct yourself in Haskell. The
issue with this is that the local system defines lots of things like
padding and alignment which mean that the layout of the structure in
memory is complex and platform specific. Tools like hsc2hs[1] or c2hs
will be very helpful here. Dealing with the variable length probably
isn't an issue. Usually variable length structures have a fixed header
and a variable tail, where the tail is an array of primitives. You can
malloc the correct sized region, use one of the previous tools to fill
in the fixed header and then use poke to complete the tail.
I might be able to be more helpful if you give the actual struct and
function prototype that you're trying to wrap.
Cheers
[1] http://therning.org/magnus/archives/tag/hsc2hs
[2] http://www.cse.unsw.edu.au/~chak/haskell/c2hs/
--
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http://www.imperialviolet.org 650-283-9641
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Re: [Haskell-cafe] Re: threads + IORefs = Segmentation fault?
On Fri, Feb 08, 2008 at 10:46:25AM +, Simon Marlow wrote: (I'm a bit behind with haskell-cafe, sorry for not seeing this sooner...) No problem! Yes, that should all be fine, because the IORef is only modified from one thread, and read from the other(s). If you were modifying the IORef from more than one thread you would need to use atomicallyModifyIORef, or MVars. If I did modify the IORef from more than one thread (e.g. if a bug were introduced), would this cause any trouble other than occasional missed updates or reads of wrong data? -- David Roundy Department of Physics Oregon State University ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Create a list without duplicates from a list with duplicates
As noted, (Data.Set.toList . Data.Set.fromList) is the best traditional solution if you don't care about order (or Data.Set.toAscList for a sorted result). If order is important, the new bijective Data.Bimap class http://code.haskell.org/~scook0/haddock/bimap/Data-Bimap.html may be your best bet (I haven't yet tried it myself). Meanwhile, here is a hand-rolled solution to order-preserving nubbing: import Data.List(groupBy,sortBy,sort) import Data.Maybe(listToMaybe) efficientNub :: (Ord a) = [a] - [a] efficientNub = flip zip [0..]-- carry along index sort -- sort by value, then index groupBy equalFsts -- group adjacent equal values map head -- keep only primus inter pares sortBy compareSnds-- sort by index map fst -- discard index where equalFsts (x1,y1) (x2,y2) = x1 == x2 compareSnds (x1,y1) (x2,y2) = compare y1 y2 x y = y . x There is a hidden proof obligation here: Exercise: Prove that (groupBy equalFsts map head) is a total function, using the defintion of groupBy from Data.List: groupBy :: (a - a - Bool) - [a] - [[a]] groupBy _ [] = [] groupBy eq (x:xs) = (x:ys) : groupBy eq zs where (ys,zs) = span (eq x) xs Felipe Lessa wrote: 2008/2/8 Jed Brown [EMAIL PROTECTED]: Look at Data.List: nub :: (Eq a) = [a] - [a] nub = nubBy (==) nubBy :: (a - a - Bool) - [a] - [a] nubBy eq [] = [] nubBy eq (x:xs) = x : nubBy eq (filter (\ y - not (eq x y)) xs) And then there's also sort :: (Ord a) = [a] - [a] which should have better performance, O(n log n) against O(n²) I guess, but of course will change the order of the elements. If you really don't mind the order at all, you could also use Data.Set in the first place. Cheers, ___ 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] Fwd: [pdxfunc] pdxfunc meeting: Monday, February 11, 7pm, CubeSpace (Portland, OR)
-- Forwarded message -- From: Igal Koshevoy [EMAIL PROTECTED] Date: Feb 8, 2008 12:01 PM Subject: [pdxfunc] pdxfunc meeting: Monday, February 11, 7pm, CubeSpace To: Igal Koshevoy [EMAIL PROTECTED] Join us at the next meeting of pdxfunc, the Portland Functional Programming Study Group. We'll have presentations, demos and discussions. We welcome programmers interested in all functional languages and our meetings have content for coders of all skill levels. If interested, please also subscribe to our mailing list at http://groups.google.com/group/pdxfunc PRESENTATIONS (1) Kevin Scaldeferri: Effortless Concurrent Programming with Erlang Abstract: Erlang is a dynamic functional programming language designed for concurrent programming. After a quick introduction to the syntax and primitives, we'll dive into some code to see example of how you can easily write programs that take advantage of multiple CPUs, and that even scale effortlessly to clusters of machines. (You are highly encouraged to download and install Erlang from http://erlang.org/download.html before the meeting.) Speaker: Kevin Scaldeferri has spent the last 6 years building high-volume, high-reliability systems at Yahoo. His interests include programming languages, the interaction between online and real-life communities, and techniques for making the development process more reliable, more successful, and more fun. (2) Tim Chevalier: Towards a GraphicsMagick Binding for Haskell Abstract: I will discuss my work in progress on implementing a Haskell Foreign Function Interface (FFI) binding for the C-based GraphicsMagick image manipulation library. I will introduce portions of the FFI through examples, as well as tools for simplifying FFI use. I will also explain how I have begun to use Haskell's type system to develop a simplified yet equally powerful interface (as compared to the C version) to the GraphicsMagick library. Given the ongoing nature of my work, I will conclude by soliciting comments on what *you* would like to see in a Haskell image manipulation library. Speaker: Tim Chevalier is a PhD student at Portland State University, where he thinks about alternative back-ends for Haskell and languages like it. He has been programming in Haskell for seven years, the first six of which he spent trying to understand monads. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
Brandon S. Allbery KF8NH wrote: On Feb 8, 2008, at 11:14 , Stefan Monnier wrote: You seem to write 12 as 1 :+ 2 instead of () :+ 1 :+ 2. But I think, the latter representation should probably be prefered. (...) How 'bout treating :+ as similar to `append' rather than similar to `cons'? Basically treat :+ as taking 2 numbers (rather than a number and a digit). Dumb questions department: why not define e.g. D'0 .. D'9 as () :* 0 .. () :* 9? Programmers then get D'1 :* 2, but the library sees () :* 1 :* 2. No, D'0 should be (), not () :* D0. If you allow () :* D0, then you introduce redundant types for the same number: In the first case, D'0 :* D'3 == D'3, and D'0 :* D'0 has no instance. In your example, D'3 and D'0 :* D'3 are equivalent, but no longer unify. Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
Dan Weston wrote: Brandon S. Allbery KF8NH wrote: On Feb 8, 2008, at 11:14 , Stefan Monnier wrote: You seem to write 12 as 1 :+ 2 instead of () :+ 1 :+ 2. But I think, the latter representation should probably be prefered. (...) How 'bout treating :+ as similar to `append' rather than similar to `cons'? Basically treat :+ as taking 2 numbers (rather than a number and a digit). Dumb questions department: why not define e.g. D'0 .. D'9 as () :* 0 .. () :* 9? Programmers then get D'1 :* 2, but the library sees () :* 1 :* 2. No, D'0 should be (), not () :* D0. If you allow () :* D0, then you introduce redundant types for the same number: In the first case, D'0 :* D'3 == D'3, and D'0 :* D'0 has no instance. In your example, D'3 and D'0 :* D'3 are equivalent, but no longer unify. Dan On second thought, how would you write D'3 :* D0 ? I think maybe using the () makes it fundamentally difficult to restrict multiple types for the same number. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] question concerning ANSI void *
On Feb 8, 2008 10:57 AM, Galchin Vasili [EMAIL PROTECTED] wrote: basically I am trying to implement ioctl for the Posix library .. so a possible signtaure would be: fdIoctl :: Fd - Int - Ptr Word 8 - IO( Ptr Word8) Ah, ok. You could cover many of the ioctls (the ones which only take a single primitive) by using the Storable class and the types CInt etc. Define the FFI call to ioctl with a type of CInt - Int - Ptr () - IO CInt and then ioctlCInt :: CInt - CInt - CInt - IO CInt ioctlCInt fd call arg = do allocaBytes $ \ptr - do poke ptr arg result - ioctl fd call (cast ptr) when (result 0) $ fail ioctl error peek ptr (untested, might work ;) ... and likewise for the other C types. However, for those ioctls which take a complex structure (e.g. many of the networking ones), you'll need to marshal yourself: data SomeIOCtlStruct = CInt CInt CInt ioctlSomeIOCtlStruct :: CInt - CInt - SomeIOCtlStruct - IO () ioctlSomeIOCtlStruct = do ... (see the above linked to pointers to hsc2hs and c2hs about how to write this function) AGL -- Adam Langley [EMAIL PROTECTED] http://www.imperialviolet.org 650-283-9641 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Create a list without duplicates from a list with duplicates
Dan Weston wrote: Meanwhile, here is a hand-rolled solution to order-preserving nubbing: import Data.List(groupBy,sortBy,sort) import Data.Maybe(listToMaybe) efficientNub :: (Ord a) = [a] - [a] efficientNub = flip zip [0..]-- carry along index sort -- sort by value, then index groupBy equalFsts -- group adjacent equal values map head -- keep only primus inter pares sortBy compareSnds-- sort by index map fst -- discard index where equalFsts (x1,y1) (x2,y2) = x1 == x2 compareSnds (x1,y1) (x2,y2) = compare y1 y2 x y = y . x I would try something like efficientNub = catMaybes . snd . mapAccumR f empty where f s x | member x s = (s, Nothing) | otherwise = (insert x s, x) that is, threading the Set of already given results through. Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: question concerning ANSI void *
Galchin Vasili wrote: Let's take a concrete but made up case .. suppose we want to call through to pthread_create and pass the (void *) argument to pthread_create which in turn gets interpreted by the pthread that is launched. How would one populate the C struct that is passed to the launched pthread keeping in mind that this C struct is variable in length? From the FFI how would one model this C struct? In this case I'd use Storable a = Ptr a and provide an instance Storable for the actual type you want to marshal. You can allocate the struct with Foreign.Marshal.Alloc.malloc and marshall it from Haskell to C with Foreign.Storable.poke. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mutable arrays
Après avoir un peu manipulé la solution de John pour qu'elle fasse la même chose que la mienne, je peux affirmer qu'elle est légèrement moins rapide (c'est infime et normal vu que ses leftFold passent plus d'informations), mais que les deux solutions ont au moins cet avantage d'être rapides (2s sur 10M de Double) et en mémoire parfaitement constante : import Data.Array.MArray import Control.Monad import Data.Array.IO import System maxArr a = liftM (foldl1' max) (getElems a) foldlA :: (MArray a e m, Ix i) = (r - e - r) - r - a i e - m r foldlA f a arr = getBounds arr = foldM (\a-a `seq` liftM $ f a) a . map (readArray arr) . range foldl1A :: (MArray a e m, Ix i) = (e - e - e) - a i e - m e foldl1A f arr = flip (foldlA f) arr = readArray arr . fst = getBounds arr foldMA :: (MArray a e m, Ix i) = (r - e - m r) - r - a i e - m r foldMA f a arr = getBounds arr = foldM (\a-a `seq` (= f a)) a . map (readArray arr) . range modifyArray :: (MArray a e m, Ix i) = (e - e) - a i e - m () modifyArray f arr = mapM_ (modifyElement f arr) . range = getBounds arr modifyElement :: (MArray a e m, Ix i) = (e - e) - a i e - i - m () modifyElement f arr i = writeArray arr i . f = readArray arr i main = do [n] - getArgs a - (newListArray (0, 10 ^ read n) [1..] :: IO (IOUArray Int Double)) maxE - foldl1A max a modifyArray (* (1/maxE)) a print = readArray a (10 ^ read n) En tout cas il serait agréable d'avoir quelques unes de ces fonctions dans les librairies standards, vu qu'elles sont généralement utiles et très efficace. Je n'utilise pas les langages fonctionnels pour avoir à écrire des boucles explicites sur mes structures de données !! ;-) (et comme on l'a vu, pour un débutant, l'écriture d'une généralisation efficace de ces boucles n'est pas si triviale qu'il y paraît). -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Create a list without duplicates from a list with duplicates
Hallo! Let's suppose I have a list [a,b,c,d,c,d]. I'd like to write a function that returns a new list without duplicates (in the example [a,b,c,d]). How can I do that? What is the most general way? I'd like to use the same function for a list of Int or String or some other user defined data type. Thank for your attention! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Create a list without duplicates from a list with duplicates
On 8 Feb 2008, [EMAIL PROTECTED] wrote: Hallo! Let's suppose I have a list [a,b,c,d,c,d]. I'd like to write a function that returns a new list without duplicates (in the example [a,b,c,d]). How can I do that? What is the most general way? I'd like to use the same function for a list of Int or String or some other user defined data type. Look at Data.List: nub :: (Eq a) = [a] - [a] nub = nubBy (==) nubBy :: (a - a - Bool) - [a] - [a] nubBy eq [] = [] nubBy eq (x:xs) = x : nubBy eq (filter (\ y - not (eq x y)) xs) Jed pgpBXoyoGoA2i.pgp Description: PGP signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Haskell maximum stack depth
Hi Yes, though testing stackGobbler with a large enough data set could be problematic for the very reason we've been discsussing. Yes you are sure, or yes you tested and the results show than neilGobbler is x% slower and consume y% more memory on specific test n? But let's say your hypothesis was correct. My hypothesis isn't that the stack is slow. AFAICT neilGobbler isn't even entirely safe as an implementation of an eager take. There's nothing the Haskell standard to stop it being transformed into.. neilGobbler :: Int - [x] - [x] neilGobbler n xs = length (take n xs) `seq` take n xs Yes, but so much in the Haskell standard is also missing. I think in this case you could reasonably argue that any compiler violating this _is_ violating the Haskell standard as it was intended (albeit not as it was written). You'll also find that the space behaviour of CAF's isn't documented in Haskell, but if people changed it you'd break quite a bit of the nofib suite. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Create a list without duplicates from a list with duplicates
2008/2/8 Jed Brown [EMAIL PROTECTED]: Look at Data.List: nub :: (Eq a) = [a] - [a] nub = nubBy (==) nubBy :: (a - a - Bool) - [a] - [a] nubBy eq [] = [] nubBy eq (x:xs) = x : nubBy eq (filter (\ y - not (eq x y)) xs) And then there's also sort :: (Ord a) = [a] - [a] which should have better performance, O(n log n) against O(n²) I guess, but of course will change the order of the elements. If you really don't mind the order at all, you could also use Data.Set in the first place. Cheers, -- Felipe. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] User groups meeting all over the world
Hi Fun in the afternoonLondon/UKFebruary 12 Fun in the afternoon is great, but its not really a user group - it is still primarily an academic event, although is open to everyone. There is LUG, which is the London Haskell Users Group, which should definately be on this list. Thanks Neil ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
You seem to write 12 as 1 :+ 2 instead of () :+ 1 :+ 2. But I think, the latter representation should probably be prefered. With it, :+ always has a number as its left argument and a digit as its right. Without the () :+ we get ugly exceptional cases. You can see this, for example, in the instance declarations for Compare. With the second representation, we could reduce the number of instances dramatically. We would define a comparison of digits (verbose) and than a comparison of numbers based on the digit comparison (not verbose). Even if () would be preferred from the programmers point of view (I'm not sure how much we could reduce the number of instances though), it makes the representation less attractive on the user-side. Anyone using the library would find it annoying and would wonder why is it neccessary. I wouldn’t wonder. Leaving out the () :* part just works because our type-level “values” are not typed, i.e., there aren’t different kinds Digit and Number but only kind *. If :+ would be a data constructor (on the value level), it would take a number and a digit argument which would forbid using a digit as its left argument. So I consider using a digit on the left as “unclean”. It’s similar to using a number as the second part of a cons cell in LISP. How 'bout treating :+ as similar to `append' rather than similar to `cons'? Basically treat :+ as taking 2 numbers (rather than a number and a digit). Stefan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Mutable arrays
Sorry for the french, I was a little bit confused... On 08/02/08, Chaddaï Fouché [EMAIL PROTECTED] wrote : After I changed John's code so that it worked on the same dataset as mine, I could benchmark both of them : My solution is a bit faster (but that's a very tiny difference and to be expected since John's fold are more general than mine), but in any case, both solution are reasonably fast (2s on a 10M Double array (unboxed)) and don't eat any more memory than necessary : Anyway it would be nice to have some version of those function in the standard library (MArray) since they are pretty useful and efficient. I don't use functional language in order to have to code explicit loops on my data structures !! ;-) (And as we saw, to write an efficient generalisation of those loops isn't as easy as it might seems) -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
On 2008-02-05, Alfonso Acosta [EMAIL PROTECTED] wrote: On Feb 5, 2008 4:10 PM, Henning Thielemann [EMAIL PROTECTED] wrote: On Fri, 1 Feb 2008, Aaron Denney wrote: On 2008-02-01, Bjorn Buckwalter [EMAIL PROTECTED] wrote: If Naturals had been sufficient for me I wouldn't have done my own implementation (I'm unaware of any other implementation of Integers). And there is certainly a lot of value to the clearer error messages from a decimal representation. I did a balanced-base-three (digits are 0, and +- 1) representation to get negative decimals. Nice. In German the digit values are sometimes called eins, keins, meins. :-) I'm almost done with the decimal library but it would be nice to check some Integer implementations for future inclusion. So, Aaron, Björn, are your implementations available somewhere? http://ofb.net/~wnoise/repos/dimensional/ -- Aaron Denney -- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I love purity, but it's killing me.
On 2/8/08, Emil Axelsson [EMAIL PROTECTED] wrote: I know of a few of ways to express sharing in a pure language: 1) Observable sharing, which, in general, is unsafe. 2) Using Template Haskell 3) Matthew Naylor has done some work on expressible sharing, which has 4) Use a monad (but I'm sure this is what you're trying to avoid). Or... 5) Forget embedding the DSL, and write a direct compiler. In addition to the sharing problem, another shortcoming of Haskell DSLs is they can not fully exploit the benefits of algebraic datatypes. Specifically, pattern matching ADTs can only be used to control the compile-time configuration of the target, it can't be used to describe the target's behavior -- at least for DSLs that generate code that executes outside of Haskell's runtime. Writing a real compiler would solve both of these problems. Is there any Haskell implementation that has a clean cut-point, from which I can start from a fully type-checked, type-annotated intermediate representation? And thanks for the link to John's paper describing Hydra's use of Template Haskell. I will definiately consider TH. -Tom ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: problem with collection (container) class
Am Freitag, 8. Februar 2008 22:14 schrieb Ben Franksen: If it's a bug then it is probably in 6.6.1 too, it just gets hidden by the fact that in 6.6.1 the -fglasgow-exts extensions cannot be activated separately. If you enable one of them, you get them all. Thanks for the info, didn't know that. The problem was the error message, which didn't mention that each type variable may appear only once in an instance head, which I had temporarily forgotten. Then the message Leandro.hs:32:0: Illegal instance declaration for `Container (Abb a b) a b' (All instance types must be of the form (T a1 ... an) where a1 ... an are distinct type *variables* Use -XFlexibleInstances if you want to disable this.) In the instance declaration for `Container (Abb a b) a b' looks rather confusing :) Cheers Ben Cheers, Daniel ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I love purity, but it's killing me.
On 2/8/08, Matthew Naylor [EMAIL PROTECTED] wrote: it in for an efficient program. However, to my knowledge, it is an unwritten rule of Haskell compilers that sharing *is* preserved, and that they do perform *graph* reduction. Clean, a similar language to I'm not sure that programmers ought to be relying on this rule. Sure, all Haskell compilers I know of preserve sharing and do graph reduction. But conventional wisdom is not the same thing as an unwritten rule. Someday, someone might come along and write a Haskell compiler that isn't based on graph reduction and doesn't preserve sharing at the implementation level (while still preserving the informal semantics of Haskell). A programmer who had written code that failed to compile correctly under this hypothetical compiler would be a very naughty Haskell programmer indeed. Haskell, indeed has a semantics based on graphs. So I don't believe Haskell doesn't have a semantics, graph-based or not... or at least not a formal one, and if not a formal one, I don't know what you mean :-) Cheers, Tim -- Tim Chevalier * http://cs.pdx.edu/~tjc * Often in error, never in doubt There are no sexist decisions to be made. There are antisexist decisions to be made. And they require tremendous energy and self-scrutiny, as well as moral stamina... -- Samuel R. Delany ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: problem with collection (container) class
Daniel Fischer wrote:
{-# LANGUAGE MultiParamTypeClasses #-}
{-# LANGUAGE FunctionalDependencies #-}
{- # LANGUAGE FlexibleInstances # -}
module Leandro where
data Abb a b = Branch a b (Abb a b) (Abb a b) | Leaf
data ListAssoc a b = Node a b (ListAssoc a b) | Empty
class Container c a b |c - a, c - b where
[...]
instance (Ord a) = Container (Abb a b) a b where
[...]
Note: The FlexibleInstances Language pragma is required by GHC 6.8.1 and
6.8.2, but not by GHC 6.6.1 or hugs, I think that's a bug in 6.8.*
If it's a bug then it is probably in 6.6.1 too, it just gets hidden by the
fact that in 6.6.1 the -fglasgow-exts extensions cannot be activated
separately. If you enable one of them, you get them all.
Cheers
Ben
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[Haskell-cafe] GHC + interactive input/output
$ cat foo.c
#include stdio.h
int
main()
{
char s[1024];
printf(gsi );
gets(s);
printf(%s\n, s);
return 0;
}
$ make foo
cc gsi.c -o gsi
$ ./foo
warning: this program uses gets(), which is unsafe.
gsi hello
hello
$ cat foo.hs
main = do
putStr gsi
s - getLine
putStrLn s
$ ghc foo.hs -o foo
$ ./foo
hello
gsi hello
(This is on MacOS X). It strikes me that GHC is being
extraordinarily unhelpful here. Is there anyone on the planet who
ever actually wants this behavior?
jcc
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Re: [Haskell-cafe] GHC + interactive input/output
On Feb 8, 2008, at 19:41 , Philip Weaver wrote: Your gsi is buffered because there's no newline at the end. To flush the buffer and force it to be printed immediately, use 'hFlush' from the System.IO library, or use 'hSetBuffering' from that same library: http://haskell.org/ghc/docs/latest/html/ libraries/base/System-IO.html I believe you can observe the same behavior in C. Most C stdio libraries in my experience have extra code in the functions that read stdin to flush stdout first, specifically because of lazy people who don't pay attention to buffering. -- brandon s. allbery [solaris,freebsd,perl,pugs,haskell] [EMAIL PROTECTED] system administrator [openafs,heimdal,too many hats] [EMAIL PROTECTED] electrical and computer engineering, carnegie mellon universityKF8NH ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
Your gsi is buffered because there's no newline at the end. To flush
the buffer and force it to be printed immediately, use 'hFlush' from the
System.IO library, or use 'hSetBuffering' from that same library:
http://haskell.org/ghc/docs/latest/html/libraries/base/System-IO.html
I believe you can observe the same behavior in C.
- Phil
On Feb 8, 2008 4:14 PM, Jonathan Cast [EMAIL PROTECTED] wrote:
$ cat foo.c
#include stdio.h
int
main()
{
char s[1024];
printf(gsi );
gets(s);
printf(%s\n, s);
return 0;
}
$ make foo
cc gsi.c -o gsi
$ ./foo
warning: this program uses gets(), which is unsafe.
gsi hello
hello
$ cat foo.hs
main = do
putStr gsi
s - getLine
putStrLn s
$ ghc foo.hs -o foo
$ ./foo
hello
gsi hello
(This is on MacOS X). It strikes me that GHC is being
extraordinarily unhelpful here. Is there anyone on the planet who
ever actually wants this behavior?
jcc
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Re: [Haskell-cafe] I love purity, but it's killing me.
tomahawkins: On 2/8/08, Emil Axelsson [EMAIL PROTECTED] wrote: I know of a few of ways to express sharing in a pure language: 1) Observable sharing, which, in general, is unsafe. 2) Using Template Haskell 3) Matthew Naylor has done some work on expressible sharing, which has 4) Use a monad (but I'm sure this is what you're trying to avoid). Or... 5) Forget embedding the DSL, and write a direct compiler. In addition to the sharing problem, another shortcoming of Haskell DSLs is they can not fully exploit the benefits of algebraic datatypes. Specifically, pattern matching ADTs can only be used to control the compile-time configuration of the target, it can't be used to describe the target's behavior -- at least for DSLs that generate code that executes outside of Haskell's runtime. Writing a real compiler would solve both of these problems. Is there any Haskell implementation that has a clean cut-point, from which I can start from a fully type-checked, type-annotated intermediate representation? Taking the output of GHC's intermediate phase, after optimising leaves you with type checked, optimised, 'Core' -- basically lambda calculus with extras. It's a good start if you then want to hand-compile that down. Extract it with -fext-core -- Don ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 4:50 PM, Brandon S. Allbery KF8NH wrote: On Feb 8, 2008, at 19:41 , Philip Weaver wrote: Your gsi is buffered because there's no newline at the end. To flush the buffer and force it to be printed immediately, use 'hFlush' from the System.IO library, or use 'hSetBuffering' from that same library: http://haskell.org/ghc/docs/latest/html/ libraries/base/System-IO.html I believe you can observe the same behavior in C. Most C stdio libraries in my experience have extra code in the functions that read stdin to flush stdout first, specifically because of lazy people who don't pay attention to buffering. Why can't GHC implement the same thing? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Implementing fixed-sized vectors (using datatype algebra?)
On Feb 6, 2008 8:47 PM, Alfonso Acosta [EMAIL PROTECTED] wrote: On Feb 7, 2008 2:30 AM, Bjorn Buckwalter [EMAIL PROTECTED] wrote: Ok. Is this what people want -- one big hold-all library with everything, as opposed to smaller more specialized packages? I guess I can see advantages (real or perceived) to both approaches. Apart from Dockins' typenats library there are no other user-friendly specific type-level libraries that know, so I cannot really tell if people would prefer a hold-all library or a couple of more granular specialized ones. Right now is not hold-all at all (it is still vaporware actually :)), so I think there's no reason to discuss that at this point. Let's see what people think. Right, of course. I'll be taking a look at your no-longer-vaporware! ;) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Slightly Offtopic in Part
Hi folks The disjunction elimination rule: I've been trying to make sense of it and I think I have had some success; however, it's far from adequate. I wonder, is there a way of demonstrating it in Haskell? A code frag with a jargon-free explanation would be mucho appreciated. Cheers, Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 5:29 PM, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. For performance, the operating system buffers writes until it is ready to write large chunks at a time. If you do not want this behavior, change the buffering mode from its default. To what? BlockBuffering is worse, not better, and the docs *explicitly* say that switching to NoBuffering will break ^D (if it wasn't broken already...) My specification for a working program is `one that works exactly like every other program on my machine'. I don't see how to produce such a program with GHC.(1) jcc (1) Using readline might work (although I'm kind of sceptical given what's preceded it), but I haven't gotten it to link thus far... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slightly Offtopic in Part
I'm assuming you mean the rule described in http://en.wikibooks.org/wiki/Formal_Logic/Sentential_Logic/Inference_Rules type Disj a b = Either a b disj_elim :: Disj a b - (a - c) - (b - c) - c disj_elim (Left a) a2c b2c = a2c a disj_elim (Right b) a2c b2c = b2c b If you know either a is true, or b is true and you know from a, I can prove c, and you know from b, I can prove c, then you can prove c. -- ryan On 2/8/08, PR Stanley [EMAIL PROTECTED] wrote: Hi folks The disjunction elimination rule: I've been trying to make sense of it and I think I have had some success; however, it's far from adequate. I wonder, is there a way of demonstrating it in Haskell? A code frag with a jargon-free explanation would be mucho appreciated. Cheers, Paul ___ 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] GHC + interactive input/output
On 8 Feb 2008, at 6:34 PM, Ryan Ingram wrote: import System.IO myGetLine = hFlush stdout getLine That fixes this issue, certainly (although it's superfluous; my program really does contain only a single call to getLine)... Nevertheless, it would be nice to at least have it in the standard library; it's much more useful than any of the input functions that already exist. jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slightly Offtopic in Part
Out of context (am I missing some earlier part of this thread?) I'm not
entirely sure what you mean.
Are you're talking about the disjunction elim rule in intuitionistic
natural deduction:
Gamma |- A + B Gamma, A |- C Gamma, B |- C
--
Gamma |- C
If so, this is just 'case'. If you annotate the rule with proof terms
(programs in the simply-typed lambda-calculus), you get the typing rule
for case:
Gamma |- e : A + B
Gamma, x1 : A |- e1 : C
Gamma, x2 : B |- e2 : C
--
Gamma |- case e of { Inl x1 - e1 ; Inr x2 - e2 } : C
I.e., when pattern matching on the following type
data Or a b =
Inl a
| Inr b
(this type is isomorphic to Either in the Prelude)
you have two cases to consider, one where you have an 'a' and the other
where you have a 'b'.
E.g., let's prove a simple theorem:
comm :: Or a b - Or b a
comm x = case x of
Inl x1 - Inr x1
Inr x2 - Inl x2
Does that help?
-Dan
On Feb09, PR Stanley wrote:
Hi folks
The disjunction elimination rule:
I've been trying to make sense of it and I think I have had some
success; however, it's far from adequate. I wonder, is there a way of
demonstrating it in Haskell? A code frag with a jargon-free
explanation would be mucho appreciated.
Cheers, Paul
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Re: [Haskell-cafe] Slightly Offtopic in Part
On Fri, Feb 08, 2008 at 06:47:51PM -0800, Ryan Ingram wrote: I'm assuming you mean the rule described in http://en.wikibooks.org/wiki/Formal_Logic/Sentential_Logic/Inference_Rules type Disj a b = Either a b disj_elim :: Disj a b - (a - c) - (b - c) - c disj_elim (Left a) a2c b2c = a2c a disj_elim (Right b) a2c b2c = b2c b If you know either a is true, or b is true and you know from a, I can prove c, and you know from b, I can prove c, then you can prove c. aka: import Data.Either type Disj = Either disj_elim = either Stefan signature.asc Description: Digital signature ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
On 8 Feb 2008, at 6:50 PM, Jonathan Cast wrote: On 8 Feb 2008, at 6:34 PM, Ryan Ingram wrote: import System.IO myGetLine = hFlush stdout getLine That fixes this issue, certainly (although it's superfluous; my program really does contain only a single call to getLine)... Nevertheless, it would be nice to at least have it in the standard library; it's much more useful than any of the input functions that already exist. Also, for some reason, this doesn't seem to be necessary inside an Emacs buffer... Do we not care about performance in that case? jcc ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GHC + interactive input/output
import System.IO myGetLine = hFlush stdout getLine -- ryan On 2/8/08, Jonathan Cast [EMAIL PROTECTED] wrote: On 8 Feb 2008, at 5:29 PM, Philip Weaver wrote: GHC certain *could* do this, but it's arguably not the right thing to do. For performance, the operating system buffers writes until it is ready to write large chunks at a time. If you do not want this behavior, change the buffering mode from its default. To what? BlockBuffering is worse, not better, and the docs *explicitly* say that switching to NoBuffering will break ^D (if it wasn't broken already...) My specification for a working program is `one that works exactly like every other program on my machine'. I don't see how to produce such a program with GHC.(1) jcc (1) Using readline might work (although I'm kind of sceptical given what's preceded it), but I haven't gotten it to link thus far... ___ 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] Slightly Offtopic in Part
For more details, look for a function called orElim in the write-up http://www.thenewsh.com/~newsham/formal/curryhoward/ Dan Ryan Ingram wrote: I'm assuming you mean the rule described in http://en.wikibooks.org/wiki/Formal_Logic/Sentential_Logic/Inference_Rules type Disj a b = Either a b disj_elim :: Disj a b - (a - c) - (b - c) - c disj_elim (Left a) a2c b2c = a2c a disj_elim (Right b) a2c b2c = b2c b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Slightly Offtopic in Part
It should be emphasized that a type needs to be inhabited by (at least one) *total* function to prove a theorem. Otherwise, you could have the following partial function purporting to prove the phony theorem that A or B implies A: phony :: Either a b - a phony (Left a) = a Dan Dan Weston wrote: For more details, look for a function called orElim in the write-up http://www.thenewsh.com/~newsham/formal/curryhoward/ Dan Ryan Ingram wrote: I'm assuming you mean the rule described in http://en.wikibooks.org/wiki/Formal_Logic/Sentential_Logic/Inference_Rules type Disj a b = Either a b disj_elim :: Disj a b - (a - c) - (b - c) - c disj_elim (Left a) a2c b2c = a2c a disj_elim (Right b) a2c b2c = b2c b ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: Finance-Quote-Yahoo 0.5.0
a new version of Finance-Quote-Yahoo has been uploaded to hackage that breaks an api of the previous version for getting bulk historical quote information. specifically, notice this updated type signature: getHistoricalQuote :: QuoteSymbol - Day - Day - QuoteFrequency - IO (Maybe [HistoricalQuote]) the QuoteFrequency can be one of Daily, Weekly, Monthly or Dividend old code using this function will break, which is why i am notifying the list explicitly of this upload. since the versioning is still 0.* and the library is listed as experimental, users should expect changes until a 1.* version is released. brad ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
