Re: [Haskell-cafe] Relaxing atomicity of STM transactions
Clojure has a commute operator whose semantics seem appropriate to your concerns: http://clojure.org/refs http://richhickey.github.com/clojure/clojure.core-api.html#clojure.core/commute Commute in haskell would be roughly :: TVar a - (a - a) - STM a. The TVar touched by commute does not get marked such that the transaction could retry. Nor is the TVar itself even updated at the time. Rather, it is read, and the result of applying some transform to it is returned. Then, when the transaction commits, the tvar is atomically modified by the function and actually updated. This works if the operation commutes with all other operations performed on the TVar anywhere else that may be running concurrently, and if no essential use (i.e. requiring atomicity) is made of the value returned from commute. Both properties can only be enforced by the discipline of the programmer. I don't know how much discussion there's been in the Clojure community about the utility of commute, as a quick google mainly reveals people trying to either figure it out or explain it. Cheers, Sterl. On Sep 28, 2010, at 7:36 PM, Tom Hawkins wrote: Thanks for the responses, but I think I should explain a bit more. I'm not interested in being able to read the live value of a TVar at any arbitrary time (via. unsafeIOToSTM). But rather I would like looslyReadTVar to have exactly the same semantics as readTVar, except that the STM runtime would not reject the transaction if the TVar is modified by another transaction before the atomic commit takes place. Also, as I would be implementing something similar in Atom, I'm not necessarily interested in a Haskell implementation, but rather if the programming experience is elevated by these alternative semantics. For example: incr :: TVar - STM () incr a = looslyReadTVar a = writeTVar a . (+ 1) decr a :: TVar - STM () decr a = readTVar a = writeTVar a . (- 1) If incr and decr where atomically started at the same time with the same TVar, decr would be rejected if incr completed first, but not the other way around. The initial reaction may be that this seriously breaks the atomicity of STM, but there may be cases where this could be useful. For instance, it allow a computationally expensive transactions to complete, even if their inputs are constantly being modified. In the embedded domain, this could be a fault monitor that reads a bunch of constantly changing sensors. -Tom ___ 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] Retargeting Haskell compiler to embedded/hardware
2010/9/29 Tom Hawkins tomahawk...@gmail.com: On Tue, Sep 28, 2010 at 9:20 PM, Shakthi Kannan shakthim...@gmail.com wrote: If you are still at it, you can have a look at Chalmers Lava [1], or Kansas Lava [2]. Feldspar [3] project targets DSP though. These are examples light embedded DSLs, i.e. sophisticated libraries where you compile, then run the program to generate code. This is not what I want. Rather, I am looking for advice on how to splice GHC -- or another implementation -- where I can build a compiler starting from a type checked, simplified Haskell AST; or better yet, an unevaluated call graph. Hi Tom, How much of GHC's Haskell do you want? If you are happy with something *similar* to Haskell, did you consider to implement (or reuse if something exists) your own concrete syntax and type checker? I would think those problems are quite lightweight in regard to writing a new backend. Cheers, Thu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Retargeting Haskell compiler to embedded/hardware
Don Stewart: tomahawkins: A few years ago I attempted to build a Haskell hardware compiler (Haskell - Verilog) based on the Yhc frontent. At the time I was trying to overcome several problems [1] with implementing a hardware description language as a light eDSL, which convinced me a proper compiler may be a better approach. Yhc was recommended as a good starting point since it had a simpler IR compared with GHC -- at least at the time. I am considering restarting this effort, but this time to target hard realtime embedded code. What is the recommended compiler to start from? I need an IR that is post type checking with as much desugaring as possible, and a code base that is relatively easy to splice and build. My other requirement is not to be bound to IO () for 'main'. The top level will be a monad, but with different semantics than IO. I would also like to reuse the standard library, with exception to the values related to IO. What are my options? Have you looked at Clash, the GHC to VHDL compiler? Links are always useful: http://clash.ewi.utwente.nl/ http://hackage.haskell.org/package/clash http://dutchhug.nl/static/dutchhugday-2010/clash.pdf http://wiki.clean.cs.ru.nl/images/8/86/Christiaan-from-haskell-to.pdf Sean ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Relaxing atomicity of STM transactions
Hi Tom, You wrote that you are interested in the programming experience with relaxed atomicity. What you are asking for are the ideas behind Twilight STM, written in these papers: http://proglang.informatik.uni-freiburg.de/projects/syncstm/techreport2010twilight.pdf (brief summary of the underlying ideas + rationale. Newer version available upon request) http://www.cs.uu.nl/research/techreps/repo/CS-2010/2010-020.pdf (about a nicer API for Twilight using Haskell + formalization. Search in the document for twilight) For experimental purposes, we have implementations in C, Java and Haskell. Annette already replied to this thread with a link to our Haskell implementation. The main idea is to change (only) the commit protocol of a transaction. The transaction (speculatively/lockless) executes as always: depending on its semantics, it may restart when it reads a value that has been modified since the start of a transaction, or if you use a multi-versioning STM, perhaps read data from older memory snapshots. What semantics you choose here is of no real concern as long as the transaction reaches its commit-point while having read data from a consistent memory snapshot. At the commit-point, however, we do something special: the programmer can provide code to manually validate the transaction using a special API. At the commit point, we first put the transaction in an irrevocable state. This ensures that at any point the programmer's validation code gives an OK, we can publish the outcome of the transaction. We then validate the transaction (without restarting) to discover inconsistencies. Finally, the validation code is executed to inspect these inconsistencies. To easily inspect these inconsistencies, you can tag all reads in the transactional body with region identifiers. In the validation code, you can then query if this region has become inconsistent, and what the new values are. These new values are again taken from a consistent memory snapshot - important! In the example that you provided, this would mean that the reference that you want to loosely read from, you tag with a special region. In the validation code, you can then easily ignore its inconsistency. Or, more likely: inspect the new value to see if the difference with the actual read value is not too big. Additionally, in the validation code, since the transaction is irrevocable, it is possible to safely do I/O, and you can change the outcome of the transaction slightly based on the new values inspected, i.e. repair the inconsistencies. These ideas provide a more fundamental way to deal with relaxed atomicity, whereas just reading loosely from a variable is not. In the latter case, you have no clue how out-dated the values are that you read, for example. Hope this is useful to you, Arie Thanks for the responses, but I think I should explain a bit more. I'm not interested in being able to read the live value of a TVar at any arbitrary time (via. unsafeIOToSTM). But rather I would like looslyReadTVar to have exactly the same semantics as readTVar, except that the STM runtime would not reject the transaction if the TVar is modified by another transaction before the atomic commit takes place. Also, as I would be implementing something similar in Atom, I'm not necessarily interested in a Haskell implementation, but rather if the programming experience is elevated by these alternative semantics. For example: incr :: TVar - STM () incr a = looslyReadTVar a = writeTVar a . (+ 1) decr a :: TVar - STM () decr a = readTVar a = writeTVar a . (- 1) If incr and decr where atomically started at the same time with the same TVar, decr would be rejected if incr completed first, but not the other way around. The initial reaction may be that this seriously breaks the atomicity of STM, but there may be cases where this could be useful. For instance, it allow a computationally expensive transactions to complete, even if their inputs are constantly being modified. In the embedded domain, this could be a fault monitor that reads a bunch of constantly changing sensors. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inverse of HaskellDB
On 28 sep 2010, at 17:33, Ozgur Akgun wrote: How do you define relationships between data types? Well, why is it any different from other fields? From one of your examples [1], I'd expect you to have a list of questions in the Quiz data type, and if necessary, a quiz field in the Question data type. This might be a bit tricky but certainly achievable [2]. This is really tricky. For example, consider storing a large tree in the database: data Tree = Node Int Tree Tree | Leaf Int This means you need to read the entire tree from the database. Or consider cyclic datastructures (such as the example you gave). How do you store this? The only way to inspect this is using a library like data-reify [1]. I think the problem might be a bit harder than you suspect. Another way to solve it is using Sebastiaan Visser's framework, described in his paper [2], but that's also rather complicated. -chris [1]: http://hackage.haskell.org/package/data-reify [2]: http://github.com/downloads/sebastiaanvisser/msc-thesis/wgp10-genstorage.pdf___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: Re[Haskell-cafe] targeting Haskell compiler to embedded/hardware
If you are really interested in embedded realtime code you may want to have a look at the timber language[1] or bit-c[2]. Another very interesting project is this[3] developing a new Haskell like language called Habit for systems programming. There are also some great papers about systems programming and problems in Haskell. For example Strongly typed memory areas programming systems-level data structures in a functional language. [1] http://www.timber-lang.org/ [2] http://www.bitc-lang.org/ [3] http://hasp.cs.pdx.edu/ [4] http://web.cecs.pdx.edu/~mpj/pubs/bytedata.pdf Tom Hawkins-2 wrote: A few years ago I attempted to build a Haskell hardware compiler (Haskell - Verilog) based on the Yhc frontent. At the time I was trying to overcome several problems [1] with implementing a hardware description language as a light eDSL, which convinced me a proper compiler may be a better approach. Yhc was recommended as a good starting point since it had a simpler IR compared with GHC -- at least at the time. I am considering restarting this effort, but this time to target hard realtime embedded code. What is the recommended compiler to start from? I need an IR that is post type checking with as much desugaring as possible, and a code base that is relatively easy to splice and build. My other requirement is not to be bound to IO () for 'main'. The top level will be a monad, but with different semantics than IO. I would also like to reuse the standard library, with exception to the values related to IO. What are my options? Thanks. -Tom [1] Lack of observable sharing; function definitions, case expressions, ADTs disappear at compile time; etc. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- View this message in context: http://old.nabble.com/Retargeting-Haskell-compiler-to-embedded-hardware-tp29834645p29836816.html 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: Parsec question (new user): unexpected end of input
Am 29.09.2010 09:54, schrieb Christian Maeder: Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. if you want to match a final tag, you could try: manyTill tagOrContent (try (aTag eof)) Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) this also looks like manyTill anyChar tagEnd C. tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inverse of HaskellDB
OK, I am rephrasing it a bit then :) I definitely don't think this would be trivial to implement. However, I'd expect a decent solution to this problem, not to have special combinators to describe relations between data types, but let the user model their data using plain haskell data types, and infer the associated table structure just by looking at the data types. I'll give this a harder thought once I find the time. There is the huge barrier of TH, stopping me from playing with things like this. Anyway, have fun! :) On 29 September 2010 10:41, Chris Eidhof ch...@eidhof.nl wrote: On 28 sep 2010, at 17:33, Ozgur Akgun wrote: How do you define relationships between data types? Well, why is it any different from other fields? From one of your examples [1], I'd expect you to have a list of questions in the Quiz data type, and if necessary, a quiz field in the Question data type. This might be a bit tricky but certainly achievable [2]. This is really tricky. For example, consider storing a large tree in the database: data Tree = Node Int Tree Tree | Leaf Int This means you need to read the entire tree from the database. Or consider cyclic datastructures (such as the example you gave). How do you store this? The only way to inspect this is using a library like data-reify [1]. I think the problem might be a bit harder than you suspect. Another way to solve it is using Sebastiaan Visser's framework, described in his paper [2], but that's also rather complicated. -chris [1]: http://hackage.haskell.org/package/data-reify [2]: http://github.com/downloads/sebastiaanvisser/msc-thesis/wgp10-genstorage.pdf -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Inverse of HaskellDB
I think this approach is not possible without involving some fairly
ugly unsafeInterleaveIO/unsafePerformIO calls. A simple example using
a common web programming example: support I have a multi-user blog
site, where each user can have multiple entries. I would model this
using standard Haskell datatypes as:
data Entry = Entry { title :: String, content :: String }
data Blogger = Blogger { name :: String, entries :: [Entry] }
Obviously we'll need some kind of blogger loading function:
getBloggerByName :: String - IO Blogger
Either this will load up all entries (a potentially incredibly costly
operation) or use unsafe IO down the road. Especially when using
database connections, this can be incredibly bad: the connection could
be closed, the SQL statement could be reused by another request, etc.
My persistent library follows a similar approach to what Chris
describes, though with a very different syntax. You can see a very
similar example on the documentation site[1].
Michael
[1] http://docs.yesodweb.com/book/persistent/#relations
On Wed, Sep 29, 2010 at 12:01 PM, Ozgur Akgun ozgurak...@gmail.com wrote:
OK, I am rephrasing it a bit then :)
I definitely don't think this would be trivial to implement. However, I'd
expect a decent solution to this problem, not to have special combinators to
describe relations between data types, but let the user model their data
using plain haskell data types, and infer the associated table structure
just by looking at the data types.
I'll give this a harder thought once I find the time. There is the huge
barrier of TH, stopping me from playing with things like this.
Anyway, have fun! :)
On 29 September 2010 10:41, Chris Eidhof ch...@eidhof.nl wrote:
On 28 sep 2010, at 17:33, Ozgur Akgun wrote:
How do you define relationships between data types?
Well, why is it any different from other fields? From one of your
examples [1], I'd expect you to have a list of questions in the Quiz data
type, and if necessary, a quiz field in the Question data type. This might
be a bit tricky but certainly achievable [2].
This is really tricky. For example, consider storing a large tree in the
database:
data Tree = Node Int Tree Tree | Leaf Int
This means you need to read the entire tree from the database. Or consider
cyclic datastructures (such as the example you gave). How do you store this?
The only way to inspect this is using a library like data-reify [1].
I think the problem might be a bit harder than you suspect.
Another way to solve it is using Sebastiaan Visser's framework, described
in his paper [2], but that's also rather complicated.
-chris
[1]: http://hackage.haskell.org/package/data-reify
[2]:
http://github.com/downloads/sebastiaanvisser/msc-thesis/wgp10-genstorage.pdf
--
Ozgur Akgun
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Re: [Haskell-cafe] ICFP2010 contest results?
Ryan Ingram wrote: I saw the winner was announced. Is there a highscore table? We were in the top 5, I want to see how well we did. Only the winners were announced at the conference - no highscore table. The organisers may put more detail on the contest website perhaps? Regards, Malcolm ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Am 29.09.2010 11:55, schrieb Christian Maeder: Am 29.09.2010 09:54, schrieb Christian Maeder: Am 29.09.2010 05:35, schrieb Peter Schmitz: [...] Error parsing file: ...\sampleTaggedContent.txt (line 4, column 1): unexpected end of input expecting The input was: [...] -- Parsers: taggedContent = do optionalWhiteSpace aTag many tagOrContent aTag many tagOrContent will consume all tags, so that no tag for the following aTag will be left. if you want to match a final tag, you could try: manyTill tagOrContent (try (aTag eof)) better yet, avoiding backtracking, return different things for aTag and someContents and check if the last entry is a tag. tagOrContent = fmap Left aTag | fmap Right someContent taggedContent = do spaces aTag l - many tagOrContent eof case reverse l of Left _ : _ - return () _ - fail expected final tag before EOF C. Cheers Christian eof return Parse complete. tagOrContent = aTag | someContent ? tagOrContent aTag = do tagBegin xs - many (noneOf [tagEndChar]) this also looks like manyTill anyChar tagEnd C. tagEnd optionalWhiteSpace return () someContent = do manyTill anyChar tagBegin return () optionalWhiteSpace = spaces -- i.e., any of \v\f\t\r\n tagBegin = char tagBeginChar tagEnd = char tagEndChar -- Etc: tagBeginChar = '' tagEndChar = '' ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Web application framework comparison?
On 28 September 2010 21:12, Jeremy Shaw jer...@n-heptane.com wrote: Not sure what that means. But I am only willing to maintain so many wiki pages. So far at least three have come up in this thread. Why? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Announce: lhae-0.0.3
lhae[1] is a spreadsheet program. It features a simple formula language and some basic statistical methods, like descriptive statistics and pivot tables. 0.0.2 - 0.0.3: --- Improvements: - Right click menu at columns/row headers and cells - Insert rows/columns between exisiting rows/columns - Boolean values - New functions: ==,/=,,=,,=,not - If-then-else expressions - New constants: true,false,pi - Filtering of columns/rows - Relative references - Copy formulas into multiple cells Fixed bugs: - Import from csv files - Table updates when deleting/inserting rows/columns - When closing tables: no more Want to save? queries on already saved tables [1] http://hackage.haskell.org/package/lhae ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: collada-output-0.1
A new graphics library: http://hackage.haskell.org/package/collada-output Most of the graphics libraries on hackage use OpenGL to visualize 3d objects. With this library you now have the choice to use an external tool for visualization and enjoy the flexibility of a standard format for 3d data exchange. I.e. one could generate a raytraced animation or load the objects in a game engine. I think that the generation of 3d objects can be much more powerful and elegant than in other languages. Since this library can be an output for some other libraries on hackage, I would agree to various changes to achieve composability of libraries. Cheers, Tillmann ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] I still cannot seem to get a GUI working under Windows.
I still cannot seem to get a GUI working under Windows. For Haskell GUI's is Ubuntu easier to setup. If so, we're losing people if Haskell GUI's are so hard to get working under Windows. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] A parsec question
I have a question about Parsec. The following program
import Control.Applicative ((*),(*))
import Text.Parsec
import Text.Parsec.Char
block p = char '{' * p * char '}'
parser = block (many digit)
main = parseTest parser {123a}
gives the output
parse error at (line 1, column 5):
unexpected a
expecting }
Note the last line mentions only '}'. I would rather like to see
expecting } or digit
since the parser could very well accept another digit here.
(1) What is the reason for this behaviour?
(2) Is there another combinator that behaves as I would like?
(3) Otherwise, how do I write one myself?
BTW, I am using parsec-3.1.0 and ghc-6.12.3.
Cheers
Ben
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[Haskell-cafe] can't find in hayoo
I need the trick to get from ByteString - [GHC.Word.Word8] and Hayoo is not helping. Super simple I expected. I haven't even tried to compile it yet. I am just trying to read in the bytes and encode with base64: import Codec.Binary.Base64 import Data.ByteString import System.Directory import System.Environment main :: do args - getArgs bFileExist - System.Directory.doesFileExist (args !! 0) let bytedata = --ByteString - [GHC.Word.Word8] if bFileExist then putStrLn $ Codec.Binary.Base64.encode bytedata else putStrlLn (File does not exist: ++ (args !! 0)) return () ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] can't find in hayoo
On Wed, Sep 29, 2010 at 11:03 AM, Roderick Ford develo...@live.com wrote: I need the trick to get from ByteString - [GHC.Word.Word8] and Hayoo is not helping. Super simple I expected. I haven't even tried to compile it yet. I am just trying to read in the bytes and encode with base64: import Codec.Binary.Base64 import Data.ByteString import System.Directory import System.Environment main :: do args - getArgs bFileExist - System.Directory.doesFileExist (args !! 0) let bytedata = --ByteString - [GHC.Word.Word8] if bFileExist then putStrLn $ Codec.Binary.Base64.encode bytedata else putStrlLn (File does not exist: ++ (args !! 0)) return () Does 'unpack' do what you want? Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] can't find in hayoo
By and large hayoo is the alta-vista of Haskell search - it has a huge database but isn't well organized or good at prioritizing. Use Hoogle when doing type-based searches for functions in the typical GHC load. http://haskell.org/hoogle/?hoogle=%3A%3A+ByteString+-%3E+[Word8] Also, what's with the non-standard module specification GHC.Word.Word8? You should use Data.Word. Cheers, Thomas On Wed, Sep 29, 2010 at 9:03 AM, Roderick Ford develo...@live.com wrote: ByteString - [GHC.Word.Word8] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] can't find in hayoo
The idea was to go from Prelude :t Data.ByteString.readFile Data.ByteString.readFile :: FilePath - IO Data.ByteString.Internal.ByteString to here Prelude :t Codec.Binary.Base64.encode Codec.Binary.Base64.encode :: [GHC.Word.Word8] - String unless there is another/easier way Roderick Date: Wed, 29 Sep 2010 09:23:37 -0700 Subject: Re: [Haskell-cafe] can't find in hayoo From: thomas.dubuis...@gmail.com To: develo...@live.com CC: haskell-cafe@haskell.org By and large hayoo is the alta-vista of Haskell search - it has a huge database but isn't well organized or good at prioritizing. Use Hoogle when doing type-based searches for functions in the typical GHC load. http://haskell.org/hoogle/?hoogle=%3A%3A+ByteString+-%3E+[Word8] Also, what's with the non-standard module specification GHC.Word.Word8? You should use Data.Word. Cheers, Thomas On Wed, Sep 29, 2010 at 9:03 AM, Roderick Ford develo...@live.com wrote: ByteString - [GHC.Word.Word8] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] can't find in hayoo
In addition to hoogle I suggest you check out hackage too. I think you'll be particularly interested in base64-bytestring: http://hackage.haskell.org/package/base64-bytestring Cheers, Thomas On Wed, Sep 29, 2010 at 9:41 AM, Roderick Ford develo...@live.com wrote: The idea was to go from Prelude :t Data.ByteString.readFile Data.ByteString.readFile :: FilePath - IO Data.ByteString.Internal.ByteString to here Prelude :t Codec.Binary.Base64.encode Codec.Binary.Base64.encode :: [GHC.Word.Word8] - String unless there is another/easier way Roderick Date: Wed, 29 Sep 2010 09:23:37 -0700 Subject: Re: [Haskell-cafe] can't find in hayoo From: thomas.dubuis...@gmail.com To: develo...@live.com CC: haskell-cafe@haskell.org By and large hayoo is the alta-vista of Haskell search - it has a huge database but isn't well organized or good at prioritizing. Use Hoogle when doing type-based searches for functions in the typical GHC load. http://haskell.org/hoogle/?hoogle=%3A%3A+ByteString+-%3E+[Word8] Also, what's with the non-standard module specification GHC.Word.Word8? You should use Data.Word. Cheers, Thomas On Wed, Sep 29, 2010 at 9:03 AM, Roderick Ford develo...@live.com wrote: ByteString - [GHC.Word.Word8] ___ 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] can't find in hayoo
YES!! Thank you so much. And thanks to Thomas also for the suggestion of using Data.ByteString.Base64 ... as the alternative method. Cheers, Roderick Date: Wed, 29 Sep 2010 11:11:01 -0500 Subject: Re: [Haskell-cafe] can't find in hayoo From: aslat...@gmail.com To: develo...@live.com CC: haskell-cafe@haskell.org On Wed, Sep 29, 2010 at 11:03 AM, Roderick Ford develo...@live.com wrote: I need the trick to get from ByteString - [GHC.Word.Word8] and Hayoo is not helping. Super simple I expected. I haven't even tried to compile it yet. I am just trying to read in the bytes and encode with base64: import Codec.Binary.Base64 import Data.ByteString import System.Directory import System.Environment main :: do args - getArgs bFileExist - System.Directory.doesFileExist (args !! 0) let bytedata = --ByteString - [GHC.Word.Word8] if bFileExist then putStrLn $ Codec.Binary.Base64.encode bytedata else putStrlLn (File does not exist: ++ (args !! 0)) return () Does 'unpack' do what you want? Antoine ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: A parsec question
Ben Franksen wrote:
import Control.Applicative ((*),(*))
import Text.Parsec
import Text.Parsec.Char
block p = char '{' * p * char '}'
parser = block (many digit)
main = parseTest parser {123a}
gives the output
parse error at (line 1, column 5):
unexpected a
expecting }
Note the last line mentions only '}'. I would rather like to see
expecting } or digit
since the parser could very well accept another digit here.
(1) What is the reason for this behaviour?
(2) Is there another combinator that behaves as I would like?
(3) Otherwise, how do I write one myself?
I just saw that Christian Maeder answered a similar question recently. I
tried his suggestion of using manyTill and bingo:
{-# LANGUAGE NoMonomorphismRestriction #-}
import Control.Applicative ((*),(*))
import Text.Parsec
block p = char '{' * p * char '}'
parser = block (manyTill digit (char '}'))
main = parseTest parser {123a}
gives
parse error at (line 1, column 5):
unexpected a
expecting } or digit
So far so good. I wonder whether this parser is as efficient as the original
one. Also, this style is less modular, as I have to mention the terminator
in two places. Is there a non-greedy variant of 'many' so that modularity
gets restored and efficiency is not lost?
Cheers
Ben
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[Haskell-cafe] Distribution needs
Hi, on planet.debian.org, there is some ill-tempered discussion about the seemingly bad relationship between the Ruby community and Debian maintainers. The following blog post summarizes the issues quite well and calmly: http://gwolf.org/blog/ruby-dissonance-debian-again With the Haskell community, luckily the relationship is much better. But since the technical situation is similar, i.e. a custom distribution channel via hackage/cabal-install, the possibility to install multiple versions of a package at once, I thought this might still be an interesting read. I hope this improves the understanding of a distribution’s needs and why we don’t like multiple versions of one package or a splitting in too many single small packages. But let me stress that I’m very happy with the interaction of the communities, Greetings, Joachim -- Joachim nomeata Breitner mail: m...@joachim-breitner.de | ICQ# 74513189 | GPG-Key: 4743206C JID: nome...@joachim-breitner.de | http://www.joachim-breitner.de/ Debian Developer: nome...@debian.org signature.asc Description: This is a digitally signed message part ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: A parsec question
On Wednesday 29 September 2010 19:10:22, Ben Franksen wrote:
Note the last line mentions only '}'. I would rather like to see
expecting } or digit
since the parser could very well accept another digit here.
parsec2 did that, I don't know whether that change is intentional or
accidental.
(1) What is the reason for this behaviour?
(2) Is there another combinator that behaves as I would like?
(3) Otherwise, how do I write one myself?
I just saw that Christian Maeder answered a similar question recently. I
tried his suggestion of using manyTill and bingo:
{-# LANGUAGE NoMonomorphismRestriction #-}
import Control.Applicative ((*),(*))
import Text.Parsec
block p = char '{' * p * char '}'
parser = block (manyTill digit (char '}'))
main = parseTest parser {123a}
gives
parse error at (line 1, column 5):
unexpected a
expecting } or digit
So far so good. I wonder whether this parser is as efficient as the
original one.
manyTill p end = scan
where
scan = do{ end; return [] }
|
do{ x - p; xs - scan; return (x:xs) }
I'm not sure, but I suspect it's less efficient.
Perhaps
manyTill' p end = scan []
where
scan acc = do { end; return (reverse acc) }
| do { x - p; scan (x:acc) }
is more efficient (depends on Parsec's bind which is more efficient), you
could test.
Also, this style is less modular, as I have to mention the
terminator in two places.
That's not the main problem. `manyTill' consumes the ending token, so
block (manyTill whatever (char '}')) needs two '}' to succeed.
You would need
block (manyTill digit (lookAhead (char '}'))
to replicate the behaviour of block (many digit).
Is there a non-greedy variant of 'many' so
that modularity gets restored and efficiency is not lost?
Cheers
Ben
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Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
There are issues, yes, and you may need the MinGW tool chain to get the GUI packages to build and install properly, but it does work. I have blogged about some of my experiences, both good and bad, at http://jpmoresmau.blogspot.com/. What GUI tool specifically do you want to use? JP On Wed, Sep 29, 2010 at 5:01 PM, cas...@istar.ca wrote: I still cannot seem to get a GUI working under Windows. For Haskell GUI's is Ubuntu easier to setup. If so, we're losing people if Haskell GUI's are so hard to get working under Windows. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- JP Moresmau http://jpmoresmau.blogspot.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
On 29 September 2010 17:01, cas...@istar.ca wrote: I still cannot seem to get a GUI working under Windows. For Haskell GUI's is Ubuntu easier to setup. If so, we're losing people if Haskell GUI's are so hard to get working under Windows. We're losing people! Charge! I think the problem is lack of Windows developers interested in GUIs, and that Windows is not so POSIXy-development-friendly as Linux or OS X. But mostly lack of people interested in that area, I think. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Monad instance for partially applied type constructor?
Hi,
I have the following code:
{-# LANGUAGE TypeSynonymInstances #-}
data Vect k b = V [(k,b)]
-- vector space over field k with basis b
-- for example, V [(5, E 1), (7, E 2)] would represent the vector 5 e1 + 7 e2
data Monomial v = M [(v,Int)]
-- monomials over variables v
-- for example, M [(A,3), (B,5)] would represent the monomial a^3 b^5
type Poly k v = Vect k (Monomial v)
-- multivariate polynomials over field k and variables v
instance Monad (Poly k) where
return v = V [(1, M [(v,1)])]
p = f = ... -- variable substitution
So my thinking is:
1. The Monad type class is for one parameter type constructors (eg [], IO)
2. Poly is a two-parameter type constructor
3. So Poly k is a one-parameter type constructor
4. What I'm trying to express, that polynomials over field k are a monad,
is true.
However, GHC 6.12.2 complains:
Type synonym `Poly' should have 2 arguments, but has been given 1
In the instance declaration for `Monad (Poly k)'
What is going wrong?
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Re: [Haskell-cafe] Monad instance for partially applied type constructor?
Maybe -XLiberalTypeSynonyms is an option:
http://www.haskell.org/ghc/docs/6.12.2/html/users_guide/data-type-extensions.html#type-synonyms
On 29 September 2010 20:08, DavidA polyom...@f2s.com wrote:
Hi,
I have the following code:
{-# LANGUAGE TypeSynonymInstances #-}
data Vect k b = V [(k,b)]
-- vector space over field k with basis b
-- for example, V [(5, E 1), (7, E 2)] would represent the vector 5 e1 + 7 e2
data Monomial v = M [(v,Int)]
-- monomials over variables v
-- for example, M [(A,3), (B,5)] would represent the monomial a^3 b^5
type Poly k v = Vect k (Monomial v)
-- multivariate polynomials over field k and variables v
instance Monad (Poly k) where
return v = V [(1, M [(v,1)])]
p = f = ... -- variable substitution
So my thinking is:
1. The Monad type class is for one parameter type constructors (eg [], IO)
2. Poly is a two-parameter type constructor
3. So Poly k is a one-parameter type constructor
4. What I'm trying to express, that polynomials over field k are a monad,
is true.
However, GHC 6.12.2 complains:
Type synonym `Poly' should have 2 arguments, but has been given 1
In the instance declaration for `Monad (Poly k)'
What is going wrong?
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Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
On Wed, 29 Sep 2010 20:08:07 +0200, you wrote: I think the problem is lack of Windows developers interested in GUIs, and that Windows is not so POSIXy-development-friendly as Linux or OS X. But mostly lack of people interested in that area, I think. There are lots of Windows developers interested in GUIs. On the whole, I'd say that Windows developers are far more focused on GUIs than non-Windows developers. (See, for example: http://mpt.net.nz/archive/2008/08/01/free-software-usability and http://daringfireball.net/2004/04/spray_on_usability for some discussion of attitudes.) The issue isn't that there aren't a lot of Windows developers who have an interest in Haskell+GUI development. The issue is that nearly every Windows developer who looks into Haskell+GUI says, This stuff sucks, and walks away, because they're interested in developing applications, not wrestling with GUI toolkits. -Steve Schafer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
I imagine that getting Haskell GUI libraries set and playing nice with the native GTK libs is a pain on Windows. That said, I know that Haskell has very nice Lua bindings and Lua has pretty mature GTK bindings. Has anyone tried developing their UI in Lua with Haskell doing all the heavy lifting? -deech On Wed, Sep 29, 2010 at 1:33 PM, Steve Schafer st...@fenestra.com wrote: On Wed, 29 Sep 2010 20:08:07 +0200, you wrote: I think the problem is lack of Windows developers interested in GUIs, and that Windows is not so POSIXy-development-friendly as Linux or OS X. But mostly lack of people interested in that area, I think. There are lots of Windows developers interested in GUIs. On the whole, I'd say that Windows developers are far more focused on GUIs than non-Windows developers. (See, for example: http://mpt.net.nz/archive/2008/08/01/free-software-usability and http://daringfireball.net/2004/04/spray_on_usability for some discussion of attitudes.) The issue isn't that there aren't a lot of Windows developers who have an interest in Haskell+GUI development. The issue is that nearly every Windows developer who looks into Haskell+GUI says, This stuff sucks, and walks away, because they're interested in developing applications, not wrestling with GUI toolkits. -Steve Schafer ___ 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 still cannot seem to get a GUI working under Windows.
On 29 September 2010 20:33, Steve Schafer st...@fenestra.com wrote: There are lots of Windows developers interested in GUIs. [..] The issue isn't that there aren't a lot of Windows developers who have an interest in Haskell+GUI development. Yeah, what do you think I meant? We're talking about the state of Haskell GUI libraries, naturally I'm talking about Haskell GUI developers. Of course Windows developers are obsessed with GUIs, I can't get anything done in a terminal on Windows. (I'm exaggerating.) The issue is that nearly every Windows developer who looks into Haskell+GUI says, This stuff sucks, and walks away, because they're interested in developing applications, not wrestling with GUI toolkits. Yeah, but not liking wrestling with libraries isn't peculiar to Haskell developers. There just needs to be enough people that the probability of there being a person who will bother to wrestle with it is high enough. Hence, the issue is lack of interest. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Monad instance for partially applied type constructor?
On Wed, Sep 29, 2010 at 11:08 AM, DavidA polyom...@f2s.com wrote:
Hi,
I have the following code:
{-# LANGUAGE TypeSynonymInstances #-}
data Vect k b = V [(k,b)]
-- vector space over field k with basis b
-- for example, V [(5, E 1), (7, E 2)] would represent the vector 5 e1 + 7 e2
data Monomial v = M [(v,Int)]
-- monomials over variables v
-- for example, M [(A,3), (B,5)] would represent the monomial a^3 b^5
type Poly k v = Vect k (Monomial v)
-- multivariate polynomials over field k and variables v
instance Monad (Poly k) where
return v = V [(1, M [(v,1)])]
p = f = ... -- variable substitution
So my thinking is:
1. The Monad type class is for one parameter type constructors (eg [], IO)
2. Poly is a two-parameter type constructor
3. So Poly k is a one-parameter type constructor
4. What I'm trying to express, that polynomials over field k are a monad,
is true.
However, GHC 6.12.2 complains:
Type synonym `Poly' should have 2 arguments, but has been given 1
In the instance declaration for `Monad (Poly k)'
What is going wrong?
Haskell doesn't have true type functions; what you are really saying is
instance Monad (\v - Vect k (Monomial v))
TypeSynonymInstances just lets you write stuff like this
type Foo = [Int]
instance C Foo where ...
instead of
type Foo = [Int]
instance C [Int] where ...
But it doesn't let you partially apply the type synonym.
On the other hand, if you did this:
newtype Compose f g a = O { unO :: f (g a) }
type Poly k = Compose (Vect k) Monomial
instance Monad (Poly k) where ...
would work, but now you have to wrap/unwrap Compose in the instance definition.
-- ryan
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Re: [Haskell-cafe] Monad instance for partially applied type constructor?
On 29 September 2010 20:48, Ryan Ingram ryani.s...@gmail.com wrote:
But it doesn't let you partially apply the type synonym.
On the other hand, if you did this:
newtype Compose f g a = O { unO :: f (g a) }
type Poly k = Compose (Vect k) Monomial
instance Monad (Poly k) where ...
would work, but now you have to wrap/unwrap Compose in the instance
definition.
LiberalTypeSynonyms lets you partially apply type synonyms.
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Re: [Haskell-cafe] Monad instance for partially applied type constructor?
On Wednesday 29 September 2010 2:52:21 pm Christopher Done wrote: LiberalTypeSynonyms lets you partially apply type synonyms. Not in general. LiberalTypeSynonyms only allows synonyms to be partially applied when expansions of other type synonyms will eventually cause them to become fully applied (or discarded, probably). So, for instance: type Foo a = (a, a) type Bar f = f Int Bar Foo == Foo Int == (Int, Int) -- valid It does not make partially applied synonyms first class, such that they'd be able to be made instances, or parameters to datatypes, etc. -- Dan ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
On Wed, 29 Sep 2010 20:44:22 +0200, you wrote: Yeah, but not liking wrestling with libraries isn't peculiar to Haskell developers. There just needs to be enough people that the probability of there being a person who will bother to wrestle with it is high enough. Hence, the issue is lack of interest. No, it isn't peculiar to Haskell developers; the problem is the one that is discussed in more detail in the two references I gave in my previous message: For the most part, developers who are attracted to open-source projects (and this certainly includes the majority of Haskell developers) simply don't think much of GUIs, and are consequently willing to release software with half-baked GUI support (at best). This is an attitude that just doesn't fly in the Windows world. Which is unfortunate, because the Windows market is HUGE compared to OS X, and STUNNINGLY HUGE compared to everything else. The fix isn't going to be to find a developer who's willing to do the work to make Haskell+GUI more seamless under Windows. The fix is for the Haskell community--as a whole--to wake up and realize what the wxWidgets folks did a while ago: Hey, you know what? This GUI stuff is _important_ if we want people to pay any attention to the software that we write! -Steve Schafer ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Help to create a function to calculate a n element moving average ??
S. Doaitse Swierstra schrieb: Avoiding repeated additions: movingAverage :: Int - [Float] - [Float] movingAverage n l = runSums (sum . take n $l) l (drop n l) where n' = fromIntegral n runSums sum (h:hs) (t:ts) = sum / n' : runSums (sum-h+t) hs ts runSums _ _ [] = [] Moving average can be interpreted as convolution (*): [1/n,1/n,1/n,...,1/n] * xs You may drop the first (n-1) values, since they average over initial padding zeros. Convolution is associative and you can decompose the first operand into simpler parts: 1/n · [1,1,1,...] * [1,0,0,,0,0,-1] * xs = 1/n · integrate ([1,0,0,,0,0,-1] * xs) Convolution is commutative, thus you could also write = 1/n · [1,0,0,,0,0,-1] * integrate xs but then integration of xs will yield unbounded values and thus higher rounding errors. This yields: movingAverage :: Int - [Float] - [Float] movingAverage n = drop (n-1) . map (/ fromIntegral n) . scanl1 (+) . (\xs - zipWith (-) xs (replicate n 0 ++ xs)) This should be the same as the implementation above, but maybe a bit nicer. :-) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Coding conventions for Haskell?
On 29/09/2010 02:18 PM, Henning Thielemann wrote: Andrew Coppin wrote: Tastes do indeed vary. To me, both of these are incorrect, and the correct way is data Foo a b = Fooa | Bar b | Foobar a b deriving (Eq, Ord) The truth is: Given the separator style of constructor definition, there is no correct way to format those declarations. :-) The correct way would be to allow terminator style. Well, yes, there is that. (And this isn't the only place in the syntax where it applies either. Tried editing export lists lately? Or Cabal module lists?) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Re: A parsec question
Daniel Fischer wrote:
On Wednesday 29 September 2010 19:10:22, Ben Franksen wrote:
Note the last line mentions only '}'. I would rather like to see
expecting } or digit
since the parser could very well accept another digit here.
parsec2 did that, I don't know whether that change is intentional or
accidental.
This looks more like a bug than a feature to me. I checked parsec-3.0.1 and
it behaves like parsec-2, i.e. behaves as I expected.
(1) What is the reason for this behaviour?
(2) Is there another combinator that behaves as I would like?
(3) Otherwise, how do I write one myself?
I just saw that Christian Maeder answered a similar question recently. I
tried his suggestion of using manyTill and bingo:
{-# LANGUAGE NoMonomorphismRestriction #-}
import Control.Applicative ((*),(*))
import Text.Parsec
block p = char '{' * p * char '}'
parser = block (manyTill digit (char '}'))
main = parseTest parser {123a}
You would need
block (manyTill digit (lookAhead (char '}'))
to replicate the behaviour of block (many digit).
Right, so it gets even more complicated.
Is there a non-greedy variant of 'many' so
that modularity gets restored and efficiency is not lost?
So many questions...
Cheers
Ben
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Re: [Haskell-cafe] Help to create a function to calculate a n element moving average ??
On 29 sep 2010, at 00:58, o...@cs.otago.ac.nz wrote: Avoiding repeated additions: movingAverage :: Int - [Float] - [Float] movingAverage n l = runSums (sum . take n $l) l (drop n l) where n' = fromIntegral n runSums sum (h:hs) (t:ts) = sum / n' : runSums (sum-h+t) hs ts runSums _ _ [] = [] Doaitse I very very carefully avoided doing any such thing in my example code. For each output result, my code does two additions and one division. Yours does one addition, one subtraction, and one division, for the required case n = 3. The way I formulated it, each calculation is independent. The way you've formulated it, the error in one calculation accumulates into the next. NOT a good idea. If this an issue then: module MovingAverage where movingAverage :: [Float] - [Float] movingAverage (x:y:l) = movingAverage' x y l where movingAverage' x y (z:zs) = (x+y+z)/3:movingAverage' y z zs movingAverage' _ _ _ = [] movingAverage _ = [] has far fewer pattern matches, Doaitse ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
On 29/09/2010 07:33 PM, Steve Schafer wrote: The issue isn't that there aren't a lot of Windows developers who have an interest in Haskell+GUI development. The issue is that nearly every Windows developer who looks into Haskell+GUI says, This stuff sucks, and walks away, because they're interested in developing applications, not wrestling with GUI toolkits. Yep, that's the one. If you want to build a GUI application in Tcl, it's going to take a couple of minutes to throw together some Tk commands and you're done. In Java, you'll have to write a mile of boilerplate, but there are wizzy tools that will write it for you. And I gather that if you've coding in C or C++ or C#, you can use VisualStudio to throw a complex GUI together in a couple of minutes. How do you do that in Haskell? Well, you can either install and configure a complete Unix emulator and then compile wxHaskell from source (?!), or you can use Gtk2hs, which still requires you to manually install and configure GTK+ and compile the entire library from source code. And even then, your developed application will only run on Windows boxes that have GTK+ installed (i.e., none of them). All of which is a far cry from install IDE, click some buttons, run the wizzard, job done. Then again, let us not claim that this is only a problem for GUI stuff. If you want to access a database, or run compression algorithms, or play sound, or do absolutely anything else which requires talking to C-land, you've going to have to face a world of pain on Windows. It seems that because this stuff is such a PITA on Windows, nobody uses Haskell on Windows. And since nobody uses Haskell on Windows, nobody is fixing these problems. So they just stay here, forever. So anyway, that's the problem. The solution is... ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Retargeting Haskell compiler to embedded/hardware
Hi Tom, The Utrecht Haskell Compiler (UHC) is internally organized as a set of compilers, for which you can configure the aspects you want. It is relatively easy to extract such a particular combination and use it as a starting point. Or you might install UHC itself and use the installed libraries, which include abstract syntax, parser, etc. There is some variation depending on what you need, so check out http://www.cs.uu.nl/wiki/UHC for initial reading, and let me know whether you need more info. regards, On 29 Sep, 2010, at 16:49 , S. Doaitse Swierstra wrote: Begin forwarded message: From: Tom Hawkins tomahawk...@gmail.com Date: 29 september 2010 03:58:11 GMT+02:00 To: haskell-cafe haskell-cafe@haskell.org Subject: [Haskell-cafe] Retargeting Haskell compiler to embedded/hardware A few years ago I attempted to build a Haskell hardware compiler (Haskell - Verilog) based on the Yhc frontent. At the time I was trying to overcome several problems [1] with implementing a hardware description language as a light eDSL, which convinced me a proper compiler may be a better approach. Yhc was recommended as a good starting point since it had a simpler IR compared with GHC -- at least at the time. I am considering restarting this effort, but this time to target hard realtime embedded code. What is the recommended compiler to start from? I need an IR that is post type checking with as much desugaring as possible, and a code base that is relatively easy to splice and build. My other requirement is not to be bound to IO () for 'main'. The top level will be a monad, but with different semantics than IO. I would also like to reuse the standard library, with exception to the values related to IO. What are my options? Thanks. -Tom [1] Lack of observable sharing; function definitions, case expressions, ADTs disappear at compile time; etc. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe - Atze - Atze Dijkstra, Department of Information and Computing Sciences. /|\ Utrecht University, PO Box 80089, 3508 TB Utrecht, Netherlands. / | \ Tel.: +31-30-2534118/1454 | WWW : http://www.cs.uu.nl/~atze . /--| \ Fax : +31-30-2513971 | Email: a...@cs.uu.nl / |___\ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Monad instance for partially applied type constructor?
Ryan Ingram ryani.spam at gmail.com writes: Haskell doesn't have true type functions; what you are really saying is instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. It appears that GHC won't let you use partially applied type synonyms as type constructors for instance declarations. Is this simply because the GHC developers didn't think anyone would want to, or is there some theoretical reason why it's hard, or a bad idea? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
On Wednesday 29 September 2010 23:02:02, Andrew Coppin wrote: So anyway, that's the problem. The solution is... Two obvious solutions. - stop using Windows and migrate to an OS where stuff works pretty much out of the box (not going to happen a lot) - start helping to make things work on Windows (maybe someday that will happen) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Monad instance for partially applied type constructor?
On Wednesday 29 September 2010 23:15:14, DavidA wrote: Ryan Ingram ryani.spam at gmail.com writes: Haskell doesn't have true type functions; what you are really saying is instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. It appears that GHC won't let you use partially applied type synonyms as type constructors for instance declarations. Is this simply because the GHC developers didn't think anyone would want to, or is there some theoretical reason why it's hard, or a bad idea? I think there was a theoretical reason why that isn't allowed (making type inference undecidable? I don't remember, I don't recall ...). For your problem, maybe data Vect k m b = Vect [(k, m b)] instance Monad (Vect k Monomial) where ... is an option? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Monad instance for partially applied type constructor?
It's hard. Here's a simple example: type Foo f = f Int class C (f :: (* - *) - *) where thingy :: f [] - f IO -- Should this ever typecheck? I would say no; there's no way to unify f [] with [Int]. callThingy :: [Int] - IO Int callThingy = thingy -- but what if you say this? instance C Foo where -- thingy :: Foo [] - Foo IO -- therefore, -- thingy :: [Int] - IO Int thingy (x:_) = return x Basically, allowing instances for type functions requires you to *un-apply* any type functions to attempt to do instance selection. -- ryan On Wed, Sep 29, 2010 at 2:15 PM, DavidA polyom...@f2s.com wrote: Ryan Ingram ryani.spam at gmail.com writes: Haskell doesn't have true type functions; what you are really saying is instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. It appears that GHC won't let you use partially applied type synonyms as type constructors for instance declarations. Is this simply because the GHC developers didn't think anyone would want to, or is there some theoretical reason why it's hard, or a bad idea? ___ 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] Re: Monad instance for partially applied type constructor?
On Wed, Sep 29, 2010 at 11:15 PM, DavidA polyom...@f2s.com wrote: Ryan Ingram ryani.spam at gmail.com writes: Haskell doesn't have true type functions; what you are really saying is instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. It appears that GHC won't let you use partially applied type synonyms as type constructors for instance declarations. Is this simply because the GHC developers didn't think anyone would want to, or is there some theoretical reason why it's hard, or a bad idea? The version of the lambda calculus (System Fc) GHC uses for its internal representation doesn't support lambdas at the type level. I've bumped up against this limitation myself, and don't know of any way to 'cheat' it (which makes sense, given that it's so fundamental). You can use newtypes, and recursive definitions (sometimes with overlap and/or fundeps) work for some cases, though they can get quite nasty in the harder ones. I have to assume upgrading the type system to support this would highly nontrivial, though I don't know exactly how high, nor what drawbacks there might be. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Work is punishment for failing to procrastinate effectively. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: I still cannot seem to get a GUI working under Windows.
Andrew Coppin wrote: On 29/09/2010 07:33 PM, Steve Schafer wrote: The issue isn't that there aren't a lot of Windows developers who have an interest in Haskell+GUI development. The issue is that nearly every Windows developer who looks into Haskell+GUI says, This stuff sucks, and walks away, because they're interested in developing applications, not wrestling with GUI toolkits. Yep, that's the one. If you want to build a GUI application in Tcl, it's going to take a couple of minutes to throw together some Tk commands and you're done. Right. In Java, you'll have to write a mile of boilerplate, but there are wizzy tools that will write it for you. And I gather that if you've coding in C or C++ or C#, you can use VisualStudio to throw a complex GUI together in a couple of minutes. Not so, at least with C++. I have used VS and C++, it is horrible. Never again. How do you do that in Haskell? Well, you can either install and configure a complete Unix emulator and then compile wxHaskell from source (?!), or you can use Gtk2hs, which still requires you to manually install and configure GTK+ and compile the entire library from source code. And even then, your developed application will only run on Windows boxes that have GTK+ installed (i.e., none of them). Can you not statically link the gtk libraries? All of which is a far cry from install IDE, click some buttons, run the wizzard, job done. I never found that this actually works. Yea, you can get *something* running pretty fast, but as soon as you start to do stuff that is not 100% standard off-the-shelf, you are screwed. *This* is when things become *really* difficult. All this compiling and installing libraries stuff is harmless, compared to the problems caused by stupidly broken APIs and crippled languages. Cheers Ben ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
RE: [Haskell-cafe] I still cannot seem to get a GUI working under Windows.
These were enough to get me started: http://www.haskell.org/haskellwiki/Opengl http://haskell.forkio.com/com-examples http://darcs.haskell.org/packages/Win32/examples/ Roderick Date: Wed, 29 Sep 2010 11:01:50 -0400 From: cas...@istar.ca To: haskell-cafe@haskell.org Subject: [Haskell-cafe] I still cannot seem to get a GUI working under Windows. I still cannot seem to get a GUI working under Windows. For Haskell GUI's is Ubuntu easier to setup. If so, we're losing people if Haskell GUI's are so hard to get working under Windows. ___ 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] Re: ICFP2010 contest results?
The organisers may put more detail on the contest website perhaps? Will do, after I get home from ICFP. - Best, Johannes. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] When I change the cabal file to say preference: base = 4
When I change the cabal file to say preference: base = 4 I still get, you are using base 3.0 which is deprecated. When I change the overall cabal profile, the error message still comes up. It seems like some other part of the install process is controlling the base version, besides the *.cabal and cabal profile file. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] When I change the cabal file to say preference: base = 4
On Thursday 30 September 2010 00:56:56, cas...@istar.ca wrote: When I change the cabal file to say preference: base = 4 In the .cabal file of a package, that would belong in the build-depends. I still get, you are using base 3.0 which is deprecated. When I change the overall cabal profile, the error message still comes up. Which cabal version? Perhaps it doesn't know preferences yet. It seems like some other part of the install process is controlling the base version, besides the *.cabal and cabal profile file. Did you verify that none of the build-depends requires base == 3.* ? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] When I change the cabal file to say preference: base = 4
On Wed, Sep 29, 2010 at 3:56 PM, cas...@istar.ca wrote: When I change the cabal file to say preference: base = 4 I still get, you are using base 3.0 which is deprecated. When I change the overall cabal profile, the error message still comes up. It seems like some other part of the install process is controlling the base version, besides the *.cabal and cabal profile file. When you run install or configure, try passing -v to see the verbose output. This can often help you see why the wrong package is picked. With base it's a bit trickier. In theory, constraints should override preferences. Base has a special thing where the preference overrides constraints when the upper bound is missing. Does the package in question have an upper bound on the version of base? Something like, base == 4.*, or base 3 base 5 ? Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Parsec question (new user): unexpected end of input
Antoine and Christian: Many thanks for your help on this thread. (I am still digesting it; much appreciated; will post when I get it working.) -- Peter ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Monad instance for partially applied type constructor?
On 09/29/2010 02:15 PM, DavidA wrote: instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. Why not: instance Monad ((-) Vect k (Monomial v)) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Monad instance for partially applied type constructor?
On 09/29/2010 09:13 PM, Alexander Solla wrote: On 09/29/2010 02:15 PM, DavidA wrote: instance Monad (\v - Vect k (Monomial v)) Yes, that is exactly what I am trying to say. And since I'm not allowed to say it like that, I was trying to say it using a type synonym parameterised over v instead. Why not: instance Monad ((-) Vect k (Monomial v)) Sorry, I guess this is a bit off. I don't think you really want a monad. I think you want something like the dual to the reader monad (i.e, a comonad) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Monad instance for partially applied type constructor?
David, Ryan Ingram wrote: Haskell doesn't have true type functions; what you are really saying is instance Monad (\v - Vect k (Monomial v)) Daniel Fischer wrote: I think there was a theoretical reason why that isn't allowed (making type inference undecidable? I don't remember, I don't recall ...). Indeed: type inference in the presence of type-level lambdas requires higher-order unification, which is undecidable [1]. Cheers, Stefan [1] Gérard P. Huet: The Undecidability of Unification in Third Order Logic Information and Control 22(3): 257-267 (1973) ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Problem with a sample from RWH
Hi, I was going over the Error Handling chapter in RWH and tried out this sample - Prelude :m Control.Exception Prelude Control.Exception let x=5 `div` 0 Prelude Control.Exception let y=5 `div` 1 Prelude Control.Exception handle (\_ - putStrLn Text) (print x) interactive:1:0: Ambiguous type variable `e' in the constraint: `Exception e' arising from a use of `handle' at interactive:1:0-39 Probable fix: add a type signature that fixes these type variable(s) Prelude Control.Exception Could someone please tell me what the problem is and how to resolve it? -- Regards, Kashyap ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with a sample from RWH
On 30 September 2010 15:23, C K Kashyap ckkash...@gmail.com wrote:
Hi,
I was going over the Error Handling chapter in RWH and tried out this sample -
Prelude :m Control.Exception
Prelude Control.Exception let x=5 `div` 0
Prelude Control.Exception let y=5 `div` 1
Prelude Control.Exception handle (\_ - putStrLn Text) (print x)
interactive:1:0:
Ambiguous type variable `e' in the constraint:
`Exception e'
arising from a use of `handle' at interactive:1:0-39
Probable fix: add a type signature that fixes these type variable(s)
Prelude Control.Exception
Could someone please tell me what the problem is and how to resolve it?
RWH was written before GHC 6.10 came out, and thus is using old-style
exceptions. As of GHC 6.10.1 with base-4, the old-style exceptions
were replaced with extensible exceptions. As such, you have two
options:
* Keep using old-style exceptions. With GHC 6.10 and 6.12, import
Control.OldException instead of Control.Exception
* Manually migrate the RWH code to new-style exceptions; there are two
ways of doing this:
- For production code, you should add explicit type signatures, etc.
for your exception-handling functions passed to handle, etc.
- For just playing around, use SomeException: e.g.: handle (\
SomeException{} - putStrLn Text) (print x)
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
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