Re: [Haskell-cafe] Ideas
Evan Laforge wrote: Indeed, you can write certain DSP algorithms beautifully in Haskell. Now, if only it could talk to the audio hardware... (Or just use common file formats even.) Oh, that's easy. I wrote an FFI interface to portaudio a while back to write a delay-looping type utility in haskell. It was pretty trivial. You could do the same for libsndfile or whatever. Well, since I can't do C... (What I typically end up doing in these situations is to write a small server program in some language that *does* have the feature I want, and then talk to it over TCP from the language that *doesn't* have the feature. But it's typically quite a lot of typing... and the only language I know of that supports sound (other than C) is Java. And it's *very* complicated...) The only thing I'm uncertain about is whether it would have good enough time and space performance. All the real work is writing yet another set of basic envelope, oscillator, and fft primitives. You *should* be able to go all the way down to the samples in pure haskell though, which would be more elegant than those other languages :) Heh. FFT is tricky. But I got it to work one time... ;-) Reaktor has abstraction. You can build a gizmo that does something useful, call it a macro, and then use it whereever you want. Well, except that if you then change your macro you have re-copy it into every instrument or ensemble or other macro that uses it. So I consider the macros basically a copy and paste mechanism. True, true... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec is being weird at me
Chris Casinghino wrote: On 8/25/07, Andrew Coppin [EMAIL PROTECTED] wrote: I thought the whole *purpose* of the endBy combinator was to keep applying one parser until the other one succeeds? I don't think this is a lookahead problem, but rather just a misreading of the spec of endBy. Here it is: (endBy p sep) parses zero or more occurrences of p, seperated and ended by sep. Returns a list of values returned by p. The key text is seperated and ended by sep. Not just ended by. ...so then what does sepEndBy do? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec is being weird at me
Chris Casinghino wrote: On 8/25/07, Chris Casinghino [EMAIL PROTECTED] wrote: I'm not sure there is a built in combinator for what you want, I guess I should have looked harder. What you want is manyTill: manyTill :: GenParser tok st a - GenParser tok st end - GenParser tok st [a] (manyTill p end) applies parser p zero or more times until parser end succeeds. Returns the list of values returned by p. Yeah, OK, that looks good... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
Evan Laforge wrote: The only thing I'm uncertain about is whether it would have good enough time and space performance. All the real work is writing yet another set of basic envelope, oscillator, and fft primitives. You *should* be able to go all the way down to the samples in pure haskell though, which would be more elegant than those other languages :) I've been playing with using Arrows as stream processors for audio, and the dataflow syntax of arrows is quite nice for sample manipulation: -- low pass filter (1-zero) lop i = proc (x, f) - do sr - readState - SampleRate let c = clip (2 * pi * f / sr) 0 1 rec y - delay i - o let o = x * c + (1 - c) * y returnA - o lop :: (ArrowCircuit a, ArrowReader b a, Floating b, Ord b) = b - a (b, b) b Unfortunately it's *very* slow - to render a 5s sine oscillator sweep from 20Hz to 2Hz through a low pass filter at 44100Hz sampling rate takes around 17s. Admittedly 40% of the time is spent outputting the numbers to a text file, but it's still far far from realtime, and churns through 7GB of memory in the process (the total memory usage at any one time is constant and small, however). Claude -- http://claudiusmaximus.goto10.org ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Files for Hugs on Zaurus
Hi Phillipa, Hugs is fast enough for me to work on the Zaurus. I packed together all the files which belong to Hugs on my Zaurus and I hope that I didnt miss something. Unpack them to /, the files will stay in usr/local/bin, usr/local/lib and usr/local/share. If you want to use Hugs not only under the console, but with pdaxqtrom (which includes a X-Server, a gcc-Compiler and tons of other stuff), go to http://www.users.on.net/~hluc/myZaurus/custom.html Please tell me, whether Hugs is working for you. Regards, Ulrich ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Style
Bjorn Bringert wrote: Here's a much more inefficient version, but it has the merit of being very easy to understand: tm_silly n = length $ takeWhile (=='0') $ reverse $ show $ product [1..n] Be careful with types - use Data.List.genericLength here instead of length. Otherwise, tm_silly n is wrong for n = 13 (on my 32-bit machine) due to round-off error in the Int type. Here is another implementation: base5 n | n 1 = [] | otherwise = let (q, r) = n `divMod` 5 in r : base5 q tm6 = sum . zipWith (*) [(5^k-1)`div`4 | k - [0..]] . base5 Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Text.Xhtml.Strict
On Sat, 25 Aug 2007, Marco Túlio Gontijo e Silva wrote: Hello there. I don't know if it's off topic, but I don't know where else to ask. I've been using Text.Xhtml.Strict, and I'm wondering why the functions are mostly Html - Html and not HTML a = a - Html, or something similar. If they were like this, and toHtml would be not needed, what would make it simpler to call the functions with arguments that are not Html. The question is specific to this library, but I think it's a very general one: isn't it better to have more generic functions with type changing inside? It seems to me that it would make things better from the users point of view. What do you think? The disadvantage of more generic types is that they reduce the possibilities of type inference by the compiler. In the case of HTML generation it might still work well, that is, you could live without type annotations.___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Converting CTime - Int
[ Sorry for the *extremely* slow response, but I'm currently working through my backlog of 6000 mails... :-P ] On Wednesday 16 May 2007 09:35, Tomasz Zielonka wrote: I wonder why CTime is not Integral - maybe there is no such guarantee for time_t? If so, then you shouldn't rely on Enum. The safest bet seems to be toRational - CTime is Real. The Single Unix Specification has the answer: http://www.opengroup.org/onlinepubs/95399/basedefs/sys/types.h.html#tag_13_67 time_t and clock_t shall be integer or real-floating types. CTime's Enum instance is as debatable as the ones for Float and Double, but for consistency reasons we included it in the FFI spec. Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
On Sat, 25 Aug 2007, Andrew Coppin wrote: Would be nice if I could build something in Haskell that overcomes these. OTOH, does Haskell have any way to talk to the audio hardware? Maybe a JACK interface? http://haskell.org/haskellwiki/Applications_and_libraries/Music_and_sound ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] :, infix operator, infix constructor, et cetera
Andrew Coppin wrote: Daniel C. Bastos wrote: But that won't compile, because it doesn't obey the syntax rules of Haskell. You could, however, write data List x = x : (List x) | End and it would work. 1 : (2 : (3 : End)) Except that (for no particularly good reason) : is a reserved symbol that always refers to the Prelude list version. You could define a similar name like: data List x = x :- (List x) | End 1 :- (2 :- (3 :- End)) Isaac ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
On Sat, 25 Aug 2007, Evan Laforge wrote: Reaktor has a few limitations though. 1. It's virtually impossible to debug the thing! (I.e., if your synth doesn't work... good luck working out why.) 2. It lacks looping capabilities. For example, you cannot build a variable-size convolution block - only a fixed-size one. (If you want to draw *a lot* of wires!) If you look through the standard library, you'll find no end of instruments that use a hack of using voice polyphony to crudely simulate looping... but it's not too hot. Would be nice if I could build something in Haskell that overcomes these. OTOH, does Haskell have any way to talk to the audio hardware? ... To get this back to haskell, at the time I wondered if a more natural implementation might be possible in haskell, seeing as it was more naturally lazy. Not sure how to implement the behaviours though (which were simply macros around a let of *dynamic-something*). I'm sure people have done plenty of signal processing, and there's always haskore... but what about a sound generation language like csound or clm or nyquist? It could fit in nicely below haskore. I'm playing around with Haskore controlling signal synthesis implemented in pure Haskell for some time now: http://darcs.haskell.org/synthesizer/src/Haskore/Interface/Signal/ It works, but it's still slow and hard to install. This discussion is certainly also of interest for the haskell-art mailing list. http://lists.lurk.org/mailman/listinfo/haskell-art ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Audio output (Was: Re: Ideas)
On Sat, 25 Aug 2007, Andrew Coppin wrote: Evan Laforge wrote: To get this back to haskell, at the time I wondered if a more natural implementation might be possible in haskell, seeing as it was more naturally lazy. Not sure how to implement the behaviours though (which were simply macros around a let of *dynamic-something*). I'm sure people have done plenty of signal processing, and there's always haskore... but what about a sound generation language like csound or clm or nyquist? It could fit in nicely below haskore. Indeed, you can write certain DSP algorithms beautifully in Haskell. Now, if only it could talk to the audio hardware... (Or just use common file formats even.) I invoke a variety of sound converters/players (sox, alsaplayer, ecasound) in order to fix this problem. Writing and playing this way is easy. Reading files is problematic because the converters cannot output header information. 'http://darcs.haskell.org/synthesizer/src/Sox/File.hs' 'http://darcs.haskell.org/synthesizer/src/Sox/Play.hs' 'http://darcs.haskell.org/dafx/src/Presentation.hs' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
On Sat, 25 Aug 2007, Andrew Coppin wrote: How easy would it be to make / would anybody care / has somebody already made ... in Haskell? - An interactive function plotter. (GNUplot is nice, but it can't plot recursive functions...) I'm be interested to use such a library. - A graphical programming tool. (You add boxes and put in lines, it constructs a program that you can run.) Would be nice for editing signal processing that is coded in Haskell. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
On Sun, 26 Aug 2007, Andrew Coppin wrote: The only thing I'm uncertain about is whether it would have good enough time and space performance. All the real work is writing yet another set of basic envelope, oscillator, and fft primitives. You *should* be able to go all the way down to the samples in pure haskell though, which would be more elegant than those other languages :) Heh. FFT is tricky. But I got it to work one time... ;-) There's already an extensive FFT implementation in Haskell by Matt Donadio: http://haskelldsp.sourceforge.net/ (I'm working on some clean up at http://darcs.haskell.org/dsp/Numeric/Transform/Fourier/ ) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Style
2007/8/26, Yitzchak Gale [EMAIL PROTECTED]: Bjorn Bringert wrote: Here's a much more inefficient version, but it has the merit of being very easy to understand: tm_silly n = length $ takeWhile (=='0') $ reverse $ show $ product [1..n] Be careful with types - use Data.List.genericLength here instead of length. Otherwise, tm_silly n is wrong for n = 13 (on my 32-bit machine) due to round-off error in the Int type. Are you sure you really tested tm_silly ? length is perfectly enough to count the 0 in n! since the number of zeros don't go over the Int limit before n = 8_589_934_615 (though this solution will stack overflow due to the product much sooned than that). -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] :, infix operator, infix constructor, et cetera
Isaac Dupree wrote: Andrew Coppin wrote: Daniel C. Bastos wrote: But that won't compile, because it doesn't obey the syntax rules of Haskell. You could, however, write data List x = x : (List x) | End and it would work. 1 : (2 : (3 : End)) Except that (for no particularly good reason) : is a reserved symbol that always refers to the Prelude list version. You could define a similar name like: Really? That's interesting... AFAIK, according to the Report, it shouldn't be. I just tested. GHC won't let me, WinHugs will. Hmm... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Norvig's Sudoku Solver in Haskell
Hello,
After reading Peter Norvig's take on writing a Sudoku solver (http://
norvig.com/sudoku.html)
I decided that I would port his program to Haskell, without changing
the algorithm, that'll make a nice exercise I thought
and should be fairly easy... Boy, was I wrong !
Anyway, I eventually managed to tiptoe around for loops, mutable
state, etc...
However, when I run my program against the test data provided (http://
norvig.com/top95.txt),
I find it takes around 1m20 s to complete (compiled with -fvia-C and -
O2, on a MacBook Pro 2.33GHz Intel Core 2 Duo).
That's roughly 8 times longer than Norvig's Python script. That's not
what I expected !
My program is also longer than the Python version.
Being a beginner, I am convinced my implementation is super naive and
non idiomatic. A seasonned Haskeller would do much shorter and much
faster. I don't know how to improve it though !
Should I introduce more strictness ? replace lists with more
efficient data structures (ByteStrings, Arrays) ?
Here is my program, and part of the profiling (memory allocation
looks huge !)
I hope this post wasn't too long. Thanks for any advice !
Emmanuel.
{-
This is an attempt to implement in Haskell, Peter Norvig's sudoku
solver :
Solving Every Sudoku Puzzle (http://norvig.com/sudoku.html)
In Norvig's program, methods which change a grid return either a new
grid, either False (failure).
Here I use Maybe, and return Just grid or Nothing in case of failure
-}
module Main where
import Prelude hiding (lookup)
import Data.List hiding (lookup)
import qualified Data.Map as M
import Control.Monad
import Maybe
import System.IO
--
-- Types
type Digit = Char
type Square = String
type Unit = [Square]
-- We represent our grid as a Map
type Grid = M.Map Square [Digit]
--
-- Setting Up the Problem
rows = ABCDEFGHI
cols = 123456789
digits = 123456789
cross :: String - String - [String]
cross rows cols = [ r:c:[] | r - rows, c - cols ]
squares :: [Square]
squares = cross rows cols -- [A1,A2,A3,...]
unitlist :: [Unit]
unitlist = [ cross rows [c] | c - cols ] ++
[ cross [r] cols | r - rows ] ++
[ cross rs cs | rs - [ABC,DEF,GHI], cs -
[123,456,789]]
units :: M.Map Square [Unit]
units = M.fromList [ (s, [ u | u - unitlist, elem s u ]) | s -
squares ]
peers :: M.Map Square [Square]
peers = M.fromList [ (s, set [[ p | p - e, p /= s ] | e - lookup s
units ]) | s - squares ]
where set = nub . concat
--
-- Wrapper around M.lookup used in list comprehensions
lookup :: (Ord a, Show a) = a - M.Map a b - b
lookup k v = case M.lookup k v of
Just x - x
Nothing - error $ Error : key ++ show k ++ not
in map !
-- lookup k m = fromJust . M.lookup k m
--
-- Parsing a grid into a Map
parsegrid :: String - Maybe Grid
parsegrid g= do regularGrid g
foldM assign allPossibilities (zip squares g)
where allPossibilities :: Grid
allPossibilities = M.fromList [ (s,digits) | s - squares ]
regularGrid :: String - Maybe String
regularGrid g = if all (\c - (elem c 0.-123456789)) g
then (Just g)
else Nothing
--
-- Propagating Constraints
assign:: Grid - (Square, Digit) - Maybe Grid
assign g (s,d) = if (elem d digits) then do -- check that we are
assigning a digit and not a '.'
let toDump = delete d (lookup s g)
res - foldM eliminate g (zip (repeat s) toDump)
return res
else return g
eliminate :: Grid - (Square, Digit) - Maybe Grid
eliminate g (s,d) = let cell = lookup s g in
if not (elem d cell) then return g -- already
eliminated
-- else d is deleted from s' values
else do let newCell = delete d cell
newV = M.insert s newCell g --
newV2 - case length newCell of
-- contradiction :
Nothing terminates the computation
0 - Nothing
-- if there is only one
value (d2) left in square, remove it from peers
1 - do let peersOfS =
[ s' | s' - lookup s peers ]
res - foldM
eliminate newV (zip peersOfS (cycle newCell))
return res
-- else : return the new
grid
_ - return newV
-- Now check
Re: [Haskell-cafe] is there a way to run tests at compile time using TH
Alex Jacobson [EMAIL PROTECTED] writes: I'd like to have code not compile if it doesn't pass the tests. Is there a way to use TH to generate compiler errors if the tests don't pass? What about something like this? import Language.Haskell.TH import Tests -- this should export testsPass :: Bool -- don't bother trying to call this function. check = $( if testsPass then [| () |] else error test failed ) main = print hi If testsPass returns False, the compiler will throw an exception during compilation, like this: Exception when trying to run compile-time code: test failed [...] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] :, infix operator, infix constructor, et cetera
On Sun, Aug 26, 2007 at 01:35:33PM +0100, Andrew Coppin wrote:
Isaac Dupree wrote:
Except that (for no particularly good reason) : is a reserved symbol
Really? That's interesting... AFAIK, according to the Report, it
shouldn't be.
It is; from http://haskell.org/onlinereport/syntax-iso.html
consym - (: {symbol | :})reservedop
reservedop - .. | : | :: | = | \ | | | - | - | @ | ~ | =
I just tested. GHC won't let me, WinHugs will. Hmm...
Sounds like a WinHugs bug if you haven't enabled extensions.
Thanks
Ian
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Re: [Haskell-cafe] is there a way to run tests at compile time using TH
On Sun, Aug 26, 2007 at 01:20:52AM -0700, Alex Jacobson wrote: I'd like to have code not compile if it doesn't pass the tests. Is there a way to use TH to generate compiler errors if the tests don't pass? This should do it, in a different module to that which defines runtests: $( case runtests of Success - return [] Failure - error Tests failed ) Thanks Ian ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] renderString problems
On Wednesday 01 August 2007 18:30, Dave Tapley wrote: I'm having a lot of trouble using renderString from Graphics.UI.GLUT.Fonts. All my attempts to render a StrokeFont have so far failed. Using a BitmapFont I can get strings to appear but they demonstrate the odd behaviour of translating themselves a distance equal to their length every time my displayCallback function is evaluated. This is actually not a bug, but a feature. :-) From the Haddock docs for renderString: Render the string in the named font, without using any display lists. Rendering a nonexistent character has no effect. If the font is a bitmap font, renderString automatically sets the OpenGL unpack pixel storage modes it needs appropriately and saves and restores the previous modes before returning. The generated call to bitmap will adjust the current raster position based on the width of the string. If the font is a stroke font, translate is used to translate the current model view matrix to advance the width of the string. The rational behind this is that you set a position once, and subsequent multiple renderString calls will render the individual strings one after the other, just like printf appends strings on the output. If this is not clear from the documentation, any suggestions how to improve the docs? And another hint: On usual consumer graphic cards, stroke fonts are normally faster than bitmapped fonts. The fastest, most flexible (scaling, filtering, ...) and visually nicest option would be textured quads, but this is not supported by GLUT. My requests are: * Does anyone know how to keep the position fixed? For bitmapped fonts, explicitly set the currentRasterPosition. For stroke fonts, you can use the normal modelview machinery (loadIdentity/preservingMatrix/...). * Are there any good examples of (working) GLUT code available on the web, I'm finding it very hard to make any progress at the moment. Certainly not at Haskell speed :( Depending on the distribution you use, you probably have the example already somewhere on your disk or you can directly have a look at the repository: http://darcs.haskell.org/packages/GLUT/examples/ Cheers, S. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] renderString problems
On 8/26/07, Sven Panne [EMAIL PROTECTED] wrote: This is actually not a bug, but a feature. :-) From the Haddock docs for renderString: Render the string in the named font, without using any display lists. Rendering a nonexistent character has no effect. If the font is a bitmap font, renderString automatically sets the OpenGL unpack pixel storage modes it needs appropriately and saves and restores the previous modes before returning. The generated call to bitmap will adjust the current raster position based on the width of the string. If the font is a stroke font, translate is used to translate the current model view matrix to advance the width of the string. The rational behind this is that you set a position once, and subsequent multiple renderString calls will render the individual strings one after the other, just like printf appends strings on the output. If this is not clear from the documentation, any suggestions how to improve the docs? Why not add the rationale to the docs too? Invoking printf should make the thing jump into focus for anyone who hasn't got it. martin ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec is being weird at me
On 8/26/07, Andrew Coppin [EMAIL PROTECTED] wrote: ...so then what does sepEndBy do? With endBy, the sequence must end with the separator, with sepEndBy, the final occurrence of the separator is optional. The documentation here is very good: http://legacy.cs.uu.nl/daan/parsec.html --Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Style
I wrote: Be careful with types - use Data.List.genericLength here instead of length. Otherwise, tm_silly n is wrong for n = 13 (on my 32-bit machine) due to round-off error in the Int type. Are you sure you really tested tm_silly ? length is perfectly enough to count the 0 in n! since the number of zeros don't go over the Int limit True, that is not the problem. Using length forces the result to be Int, which is different than all of the other tm's so far. So for example, try this: [n | n - [0..25], tm_silly n /= tm n] -Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] nested datatypes
Hi there.
recently I was trying to represent complex data by defining several
datatypes and nesting them, such as
data Foo = Foo { foo :: Bar }
deriving (Eq,Show)
data Bar = Bar { bar :: Int }
deriving (Eq,Show)
To change only a part of the data, syntactic sugar is quite convenient. But
it seems to be quite painful with nested datatypes.
b = Bar 10
f = Foo b
foobar :: Int - Foo - Foo
foobar i f =
let nb = (foo f){bar = i}
in f{foo = nb}
So, my question is : is there a nifty way to modify data within a nested
datatype, similar to the f{foo = bar} style ? If not, anyone is using some
kind of workaround for this ?
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Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
On Sun, 2007-08-26 at 14:50 +0200, manu wrote: Hello, After reading Peter Norvig's take on writing a Sudoku solver (http:// norvig.com/sudoku.html) I decided that I would port his program to Haskell, without changing the algorithm, that'll make a nice exercise I thought and should be fairly easy... Boy, was I wrong ! Anyway, I eventually managed to tiptoe around for loops, mutable state, etc... However, when I run my program against the test data provided (http:// norvig.com/top95.txt), I find it takes around 1m20 s to complete (compiled with -fvia-C and - O2, on a MacBook Pro 2.33GHz Intel Core 2 Duo). That's roughly 8 times longer than Norvig's Python script. That's not what I expected ! My program is also longer than the Python version. Being a beginner, I am convinced my implementation is super naive and non idiomatic. A seasonned Haskeller would do much shorter and much faster. I don't know how to improve it though ! Should I introduce more strictness ? replace lists with more efficient data structures (ByteStrings, Arrays) ? Yes. Treating lists like arrays is always a recipe for heartbreak. If you did want to try to match the python code exactly there are mutable arrays and such. http://www.haskell.org/haskellwiki/Sudoku has a bunch of different implementations going for different things. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
manu [EMAIL PROTECTED]: After reading Peter Norvig's take on writing a Sudoku solver (http:// norvig.com/sudoku.html) I decided that I would port his program to Haskell Your program was wrapped by your mail client, so you may want to hpaste your program for easier digestion. Being a beginner, I am convinced my implementation is super naive and non idiomatic. A seasonned Haskeller would do much shorter and much faster. I don't know how to improve it though ! Disclaimer: I'm not an experienced Haskeller either, and I haven't had a real look at your code at all. The following is only what stroke me by a quick look. Gurus may eventually reduce your code into a thirty-line version that also runs quickly. -- Types type Digit = Char type Square = String type Unit = [Square] -- We represent our grid as a Map type Grid = M.Map Square [Digit] Your profiling output suggests that much time is consumed by the lookup function. Since you're using (fromJust . lookup) everywhere anyway, a data structure not envolving the Maybe type is probably a more succint choice. And why bother with characters and strings? So I propose type Square = (Int,Int) type Grid = Array Square Int -- or [Int], if the algorithm requires that Where the array's bound are (0,0), (8,8) or (1,1), (9,9), according to your taste. newV2 - case length newCell of 0 - Nothing 1 - do let peersOfS = [ s' | s' - lookup s peers ] res - foldM eliminate newV (zip peersOfS (cycle newCell)) return res _ - return newV The use of “length” here is not an actual performance problem, but unnecessary. Simply write: case newCell of [] - ... [_] - ... _ - ... The same is valid for your other use of length. Malte ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Ideas
+++ Andrew Coppin [Aug 25 07 12:50 ]: How easy would it be to make / would anybody care / has somebody already made ... in Haskell? - A wiki program. (Ditto.) I wrote a simple wiki using HAppS and pandoc. See demonstration #15 on the pandoc web page: http://sophos.berkeley.edu/macfarlane/pandoc/examples.html It's by no means a finished product, but might serve as a good base if you decide to work on a wiki. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Hugs on Zaurus
2007/8/26, Ulrich Vollert [EMAIL PROTECTED]: Haskell could run on such a platform. Ofcourse this is completly other way around in terms of power and memory. :) But anyway, did anyone do it? I compiled Hugs for my Sharp Zaurus SL-C3200 (http://www.trisoft.de) which is a PDA with an ARM processor. (System: Lineo uLinux , CPU: Intel(r) XScale™ (PXA270, 416 MHz)) Hugs was compiled by gcc 2.95.3 and can be used in the console, additionally under a special X/Qt-Environment called pdaXqtrom (http://www.users.on.net/~hluc/myZaurus/). So, it is possible to use graphics on the Zaurus, too. I didnt dare to port ghc or Yhc - which would be great to use on the Zaurus, too. This is so cool. Unfortunatly I own Treo 650 and running Linux here is a lot of hackery. It would be awsomely cool to use Hugs on it. Cheers, Radek. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Ideas
John MacFarlane wrote: +++ Andrew Coppin [Aug 25 07 12:50 ]: I wrote a simple wiki using HAppS and pandoc. See demonstration #15 on the pandoc web page: http://sophos.berkeley.edu/macfarlane/pandoc/examples.html o Hey ! that s exactly whatI had in mind.. cool indeed, I am toying with the idea to - produce book, nicely (automatically) typeset with Latex or docbook - out of a wiki as interface ( as wikibook for instance) - with either free and informal text , - or formally ( automatically produced) sets or reference or docs ( a bit like literate programming embed code into the text), but these table would be more and more refined set of requirement.. This last point was with a software ingeniering backgroud in mind, ie to produce the requirement, and specification of software, , imagine a lot of reference and cross reference to manage, and to establish tracability..( if you heard about Cleanroom, just to examplify ) may i ask you what did you had in mind as an application when you started that ? -- View this message in context: http://www.nabble.com/Ideas-tf4327747.html#a12337130 Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: nested datatypes
(Note that the term nested data type also/already carries the meaning
non-regular data type, an example being
data PerfectBinaryTree a = One a | Succ (PerfectBinaryTree (a,a))
)
Thomas Girod wrote:
recently I was trying to represent complex data by defining several
datatypes and nesting them, such as
data Foo = Foo { foo :: Bar }
deriving (Eq,Show)
data Bar = Bar { bar :: Int }
deriving (Eq,Show)
To change only a part of the data, syntactic sugar is quite convenient. But
it seems to be quite painful with nested datatypes.
b = Bar 10
f = Foo b
foobar :: Int - Foo - Foo
foobar i f =
let nb = (foo f){bar = i}
in f{foo = nb}
So, my question is : is there a nifty way to modify data within a nested
datatype, similar to the f{foo = bar} style ? If not, anyone is using some
kind of workaround for this ?
There is a nifty way, called functional references. They're a pair of
get and set functions
data Ref s a = Ref { get :: s - a, set :: a - s - s }
The nice thing about them is that we can compose them like functions
o :: Ref b c - Ref a b - Ref a c
f `o` g = Ref (get f . get g) (\c a - set (set c f $ get g a) g a)
The example becomes
data Foo = Foo Bar
data Bar = Bar Int
foo :: Ref Foo Bar
foo = Ref (\(Foo x) - x) (\x (Foo _) - Foo y)
bar :: Ref Bar Int
bar = Ref (\(Bar x) - x) (\x (Bar _) - Bar x)
foobar :: Ref Foo Int
foobar = bar `o` foo
See also
http://luqui.org/blog/archives/2007/08/05/
haskell-state-accessors-second-attempt-composability/
and
Sander Evers, Peter Achten, and Jan Kuper. A Functional Programming
Technique for Forms in Graphical User Interfaces.
http://www.st.cs.ru.nl/papers/2005/eves2005-FFormsIFL04.pdf
Writing getter and setter functions by hand can be tedious but somebody
already automated this with Template Haskell or other other
preprocessing tools.
Regards,
apfelmus
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[Haskell-cafe] Re: Ideas
may i ask you what did you had in mind as an application when you started that ? This was just recreational programming: I wanted to see what writing a web application in Haskell would be like. I think it would be great to have a fully featured wiki program in Haskell, but I don't have time to do it myself. Your idea sounds very interesting. Feel free to extend pandocwiki if that works for you; it's GPL. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Parsec is being weird at me
Chris Casinghino wrote: On 8/26/07, Andrew Coppin [EMAIL PROTECTED] wrote: ...so then what does sepEndBy do? With endBy, the sequence must end with the separator, with sepEndBy, the final occurrence of the separator is optional. Oh. I see... *sigh* Another wetware error. :-/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
Hi Manu, You wrote: After reading Peter Norvig's take on writing a Sudoku solver (http:// norvig.com/sudoku.html) I decided that I would port his program to Haskell, without changing the algorithm, that'll make a nice exercise I thought and should be fairly easy... Boy, was I wrong ! Welcome to the Haskell Sudoku club! http://haskell.org/haskellwiki/Sudoku Please add your solver there. I enjoyed reading your solver, and comparing it to the Python version. It was a nice idea to port the imperitive parts of this algorithm using the Maybe monad. The algorithm of your solver is essentially identical to the solver I posted on the wiki page; even the data structures are more or less the same. But mine is written in a more native Haskell style (happens to be based on a State monad). When I run my program against the test data provided (http://norvig.com/top95.txt), I find it takes around 1m20 s to complete I just ran mine against that file, also on a MacBook like yours, but only 2Ghz. It took about 28s, only about double Norvig's claim. There are other solvers on the wiki page that claim to be considerably faster. (compiled with -fvia-C The GHC gurus can correct me, but I understand that there isn't likely to be any advantage to -fvia-C nowadays. My program is also longer than the Python version. Yes, but for porting foreign code I think you did great. The use of strings, copied from the Python, looks a bit arcane in Haskell, but it shouldn't hurt anything. Perhaps you would gain something if you used Data.Map.! instead of your lookup. Other than that, I'm not sure why your code runs slower than mine. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
Manu wrote: Should I introduce more strictness ? replace lists with more efficient data structures (ByteStrings, Arrays) ? Derek wrote: Yes. Treating lists like arrays is always a recipe for heartbreak. Here it costs very little - the lists are all short, mostly of length exactly 9. If you did want to try to match the python code exactly there are mutable arrays and such. I think Manu's code is about as exact as you can get for a direct translation into pure Haskell. You could emulate Python using imperitive-style Haskell, but that would be a different sort of port. If speed is really important for you, there are many ways to optimize a Haskell program - the techniques Derek mentioned, and many more, all the way down to low-level bit fiddling on the bare metal. There are some great people on this list who are very, very good at that. But I personally find that for my own purposes, pure, simple, clear Haskell is almost always more than fast enough. And it saves truckloads of debugging time. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
From: Malte Milatz [EMAIL PROTECTED] Subject: Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell Your program was wrapped by your mail client, so you may want to hpaste your program for easier digestion. here it is : http://hpaste.org/2452 Your profiling output suggests that much time is consumed by the lookup function. Since you're using (fromJust . lookup) everywhere anyway, a data structure not envolving the Maybe type is probably a more succint choice. And why bother with characters and strings? no rationale except that's what the original Python script did use newV2 - case length newCell of 0 - Nothing 1 - do let peersOfS = [ s' | s' - lookup s peers ] res - foldM eliminate newV (zip peersOfS (cycle newCell)) return res _ - return newV The use of “length” here is not an actual performance problem, but unnecessary. Simply write: case newCell of [] - ... [_] - ... _ - ... The same is valid for your other use of length. Malte I see, thanks ! E.D ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] arrows-.02 fails when rebuilding ghc 6.6.1
I try download and build 6.6.1 ( as ubntu has just 6.6 on package) and most went ok ( compiler and most libs) but arrows i tried and download arrow 0.2 from hackage but no more success any ideas ? ( knowing 6.6 is also on the machine if that matters) [EMAIL PROTECTED]:~/src/arrows-0.2$ runghc Setup.hs build Preprocessing library arrows-0.2... Building arrows-0.2... [ 1 of 13] Compiling Data.Stream ( Data/Stream.hs, dist/build/Data/Stream.o ) [ 2 of 13] Compiling Control.Arrow.Transformer ( Control/Arrow/Transformer.hs, dist/build/Control/Arrow/Transformer.o ) [ 3 of 13] Compiling Control.Arrow.Operations ( Control/Arrow/Operations.hs, dist/build/Control/Arrow/Operations.o ) [ 4 of 13] Compiling Control.Arrow.Transformer.CoState ( Control/Arrow/Transformer/CoState.hs, dist/build/Control/Arrow/Transformer/CoState.o ) [ 5 of 13] Compiling Control.Arrow.Internals ( Control/Arrow/Internals.hs, dist/build/Control/Arrow/Internals.o ) [ 6 of 13] Compiling Control.Arrow.Transformer.Automaton ( Control/Arrow/Transformer/Automaton.hs, dist/build/Control/Arrow/Transformer/Automaton.o ) Control/Arrow/Transformer/Automaton.hs:98:0: Illegal instance declaration for `ArrowWriter w (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowWriter w (Automaton a)' Control/Arrow/Transformer/Automaton.hs:104:0: Illegal instance declaration for `ArrowError r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowError r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:115:0: Illegal instance declaration for `ArrowReader r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowReader r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:120:0: Illegal instance declaration for `ArrowState s (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowState s (Automaton a)' Control/Arrow/Transformer/Automaton.hs:126:0: Illegal instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowAddWriter w (Automaton a) (Automaton a')' I discovered recently that my ubuntu package were providing only 6.6 and the latest cabal needs 6.6.1. when rebuilding this one from the tar ( not the head on darcs) most went ok but the arrows lib. I also tried to get it from hackage, but idem: ( I also have 6.6 on the machaine dos it matters ?) here is the build from hacakge with runghc : [EMAIL PROTECTED]:~/src/arrows-0.2$ runghc Setup.hs build Preprocessing library arrows-0.2... Building arrows-0.2... [ 1 of 13] Compiling Data.Stream ( Data/Stream.hs, dist/build/Data/Stream.o ) [ 2 of 13] Compiling Control.Arrow.Transformer ( Control/Arrow/Transformer.hs, dist/build/Control/Arrow/Transformer.o ) [ 3 of 13] Compiling Control.Arrow.Operations ( Control/Arrow/Operations.hs, dist/build/Control/Arrow/Operations.o ) [ 4 of 13] Compiling Control.Arrow.Transformer.CoState ( Control/Arrow/Transformer/CoState.hs, dist/build/Control/Arrow/Transformer/CoState.o ) [ 5 of 13] Compiling Control.Arrow.Internals ( Control/Arrow/Internals.hs, dist/build/Control/Arrow/Internals.o ) [ 6 of 13] Compiling Control.Arrow.Transformer.Automaton ( Control/Arrow/Transformer/Automaton.hs, dist/build/Control/Arrow/Transformer/Automaton.o ) Control/Arrow/Transformer/Automaton.hs:98:0: Illegal instance declaration for `ArrowWriter w (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowWriter w (Automaton a)' Control/Arrow/Transformer/Automaton.hs:104:0: Illegal instance declaration for `ArrowError r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowError r (Automaton a)' Control/Arrow/Transformer/Automaton.hs:115:0: Illegal instance declaration for `ArrowReader r (Automaton a)' (the Coverage Condition fails for one of the functional dependencies; Use -fallow-undecidable-instances to permit this) In the instance declaration for `ArrowReader r (Automaton a)'
Re: [Haskell-cafe] arrows-.02 fails when rebuilding ghc 6.6.1
On Sun, Aug 26, 2007 at 11:16:17PM +0200, Luc TAESCH wrote: I try download and build 6.6.1 ( as ubntu has just 6.6 on package) and most went ok ( compiler and most libs) but arrows i tried and download arrow 0.2 from hackage but no more success You need to change the Extensions line in arrows.cabal to Extensions: MultiParamTypeClasses, UndecidableInstances ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Ideas
thanks John for replying... when building , i cannot find the lcs mentionned in the cabal file not on hasckage nor on goggle. could you help? ( your papers on philosophy looks quite serious .. impressive you are in haskell too .. math backgroud ? logics ?) 2007/8/26, John MacFarlane [EMAIL PROTECTED]: may i ask you what did you had in mind as an application when you started that ? This was just recreational programming: I wanted to see what writing a web application in Haskell would be like. I think it would be great to have a fully featured wiki program in Haskell, but I don't have time to do it myself. Your idea sounds very interesting. Feel free to extend pandocwiki if that works for you; it's GPL. John ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Norvig's Sudoku Solver in Haskell
I wrote: Perhaps you would gain something if you used Data.Map.! instead of your lookup. Manu wrote: I'm not sure I understand, do you mean I should have use a strict Map constructor ? like : Map !key !value ? No, there is an operator in Data.Map called !. how can it replace the lookup function ? Use import qualified Data.Map as M import Data.Map (!) Then, instead of lookup k m use m ! k. Other than that, I'm not sure why your code runs slower than mine. Malte Milatz wrote: MM The use of length here is not an actual MM performance problem... Maybe not there, but I think Malte's suggestion might actually improve performance if you do the same thing a few lines further down, where you wrote: case length dPlaces of By using Malte's idea there instead of length, you might allow some calculations inside dPlaces to be lazily skipped. Regards, Yitz ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Ideas
lcs can be found at http://urchin.earth.li/darcs/igloo/lcs/ +++ Luc TAESCH [Aug 26 07 23:45 ]: when building , i cannot find the lcs mentionned in the cabal file not on hasckage nor on goggle. could you help? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Style
2007/8/26, Yitzchak Gale [EMAIL PROTECTED]: True, that is not the problem. Using length forces the result to be Int, which is different than all of the other tm's so far. So for example, try this: [n | n - [0..25], tm_silly n /= tm n] You mean to say that tm_silly returns Int, which means we can't use it directly in a comparison but have to use toInteger or fromInteger ? Ok, in this case, but it's still a nice test for our more optimized functions (and using genericLength is much slower than toInteger . length, though of course the results differ for really long list) $ [n | n - [1..1000], toInteger (tm_silly n) /= tm n] [] -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Help understanding a partial application
Hi, I was browsing through the source code for Data.Foldable and having trouble comprehending it (which was kind of the point of browsing the code, so I could learn something ;) ) I'm looking at foldl foldl :: (c - d - c) - c - t d - c foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z But, I haven't got very far. I'm still trying to follow: Endo . flip f f is of type c-d-c, so this makes flip f of type d-c-c. I think the Endo constructor is of type (a-a)-Endo a I think a is binding to a function type here, but can not work out what. (From memory) ghci reports :t Endo . flip (+) Num a = a - Endo a So, this looks like a partial application of the constructor? But, this still isn't helping me understand. Any thoughts or pointers that might help me comprehend what's happening? Thanks, Levi lstephen.wordpress.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Geometry
-BEGIN PGP SIGNED MESSAGE- Hash: SHA1 I went camping on the weekend and a friend of mine who is a builder asked me many questions on geometry as they apply to his every day work - - most of which I could answer. However, there was one that I couldn't and I am having trouble googling a solution (for lack of keywords?). I'm hoping a fellow Haskeller could help me out (in Haskell of course). The problem is finding the unknown x from the two knowns a and b in the given image below (excuse my Microsoft Paintbrush skills). I may have misunderstood his problem (we were drawing in dirt) and actually, it is the straight line between the two points on the circumference that are known and not the specified 'b', but I figure I could derive one solution from another if I have misunderstood him. Here is my image: http://tinyurl.com/2kgsjy Thanks for any tips or keywords with which to google! - -- Tony Morris http://tmorris.net/ -BEGIN PGP SIGNATURE- Version: GnuPG v1.4.6 (GNU/Linux) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFG0iM6mnpgrYe6r60RAqfDAJ4gFAdr7zP1ehLl8H2MaCzCNfAvhQCgmL8D 4nrxrK13O9EBNv/ojPIMJXI= =eaxX -END PGP SIGNATURE- ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Geometry
Hi Tony, x is called the sagitta. At least when making a telescope mirror it is[1]. By bisecting your angle with another radius, you'll see that you have a right triangle with hypotenuse a, and legs of length (b/2) and (a-x). Then sagitta a b = a - sqrt (a*a - b*b/4) Considered as a function of half the angle subtended by the points on the circumference, this is called the versine. http://en.wikipedia.org/wiki/Versine [1] http://www.stellafane.com/atm/atm_grind/atm_measure_sag.htm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Geometry
You've got a which is the radius of the circle, and b which is the length of the arc, thus you've got the angle between the two red radiuses : u = b / a So with basic trigonometry, we can deduce a - x = a * cos(u/2) x = a *( cos(u/2) - 1) -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Geometry
On Mon, Aug 27, 2007 at 11:04:58AM +1000, Tony Morris wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 I went camping on the weekend and a friend of mine who is a builder asked me many questions on geometry as they apply to his every day work - - most of which I could answer. However, there was one that I couldn't and I am having trouble googling a solution (for lack of keywords?). I'm hoping a fellow Haskeller could help me out (in Haskell of course). The problem is finding the unknown x from the two knowns a and b in the given image below (excuse my Microsoft Paintbrush skills). I may have misunderstood his problem (we were drawing in dirt) and actually, it is the straight line between the two points on the circumference that are known and not the specified 'b', but I figure I could derive one solution from another if I have misunderstood him. Here is my image: http://tinyurl.com/2kgsjy This is a fairly simple exercise in trigonometry. Call the angle subtended by b, θ. Then: b = a sin(θ/2) a - x = a cos(θ/2) by the relation between circles and trig functions. From this we can (algebraicly) derive: sin(θ/2) = b / a x = a - a cos(θ/2) x = a - a (1 - b² / a²)^½ (nb, I'm assuming θ is less than 180° here) And as you request: problem a b = a - a * sqrt (1 - b*b / a*a) 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] Geometry
2007/8/27, Chaddaï Fouché [EMAIL PROTECTED]: You've got a which is the radius of the circle, and b which is the length of the arc, thus you've got the angle between the two red radiuses : u = b / a So with basic trigonometry, we can deduce a - x = a * cos(u/2) x = a *( cos(u/2) - 1) -- Jedaï Actually that would be x = a * (1 - cos (b/(2a))) Ooops o_O -- Jedaï ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Geometry
On Mon, 27 Aug 2007 11:04:58 +1000, you wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 I went camping on the weekend and a friend of mine who is a builder asked me many questions on geometry as they apply to his every day work - - most of which I could answer. However, there was one that I couldn't and I am having trouble googling a solution (for lack of keywords?). I'm hoping a fellow Haskeller could help me out (in Haskell of course). The problem is finding the unknown x from the two knowns a and b in the given image below (excuse my Microsoft Paintbrush skills). I may have misunderstood his problem (we were drawing in dirt) and actually, it is the straight line between the two points on the circumference that are known and not the specified 'b', but I figure I could derive one solution from another if I have misunderstood him. Here is my image: http://tinyurl.com/2kgsjy Thanks for any tips or keywords with which to google! So a is the radius of the circle, and b is half the length of the chord. From basic trigonometry: b = a * sin @ where @ is half of the angle between the two radii as drawn in the picture. Then: x = a * (1 - cos @) Using the trigonometric identity sin^2 @ + cos^2 @ = 1 and rearranging, we get: x = a - sqrt(a^2 - b^2) I don't know offhand if there's a straightforward way to arrive at this result without using trigonometry. By the way, I found http://www.1728.com/circsect.htm by Googling height chord. Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Geometry
On Sun, 26 Aug 2007 21:30:30 -0400, you wrote: I don't know offhand if there's a straightforward way to arrive at this result without using trigonometry. Duh. Of course there is Steve Schafer Fenestra Technologies Corp. http://www.fenestra.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Help understanding a partial application
Just expand out the function composition: Dual . Endo . flip f = (\x - Dual (Endo (flip f x))) which has the type d - Dual (Endo c). -- ryan On 8/26/07, Levi Stephen [EMAIL PROTECTED] wrote: Hi, I was browsing through the source code for Data.Foldable and having trouble comprehending it (which was kind of the point of browsing the code, so I could learn something ;) ) I'm looking at foldl foldl :: (c - d - c) - c - t d - c foldl f z t = appEndo (getDual (foldMap (Dual . Endo . flip f) t)) z But, I haven't got very far. I'm still trying to follow: Endo . flip f f is of type c-d-c, so this makes flip f of type d-c-c. I think the Endo constructor is of type (a-a)-Endo a I think a is binding to a function type here, but can not work out what. (From memory) ghci reports :t Endo . flip (+) Num a = a - Endo a So, this looks like a partial application of the constructor? But, this still isn't helping me understand. Any thoughts or pointers that might help me comprehend what's happening? Thanks, Levi lstephen.wordpress.com ___ 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] Help understanding a partial application
Ryan Ingram wrote: Just expand out the function composition: Dual . Endo . flip f = (\x - Dual (Endo (flip f x))) which has the type d - Dual (Endo c). -- ryan Aha. I didn't get this straight away, but once I looked at the type signature for function composition, it became clear. Thanks, Levi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
