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: [Haskell-cafe] Inverse of HaskellDB
Hey Jonathan, I've done some work on this. The hard part is defining relationships between datatypes: how do you model this in Haskell? I've some code on github: http://github.com/chriseidhof/persist, you might be interested in that. -chris On 25 sep 2010, at 21:31, Jonathan Geddes wrote: Cafe, HaskellDB takes a database schema and produces Haskell data structures (plus some other query-related stuff for its EDSL query language). What I'm looking for is the inverse of this functionality. I want to create tables based on a Haskell data structure with a few simple rules. These rules include: if a field is not of the form `Maybe a' then it can't be nullable in the database. If a field is not a primitive (in the database) then it is actually stored in another table and a reference id is stored in the table. Tables are produced recursively, unless they already exist, etc. The HaskellDB approach is great for interfacing with existing tables, but in my case I already have data structures and now I would like a quick way to create tables to persist them. Does such a thing exist? If not, would you find it useful? I may take this up as a side project if it does not already exist and others would find it useful. Thanks, --Jonathan ___ 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] record update
For completeness, using fclabels (yet another record package) you can write it
like this:
{-# LANGUAGE TemplateHaskell #-}
module Records where
import Data.Record.Label
data MyRecord = MyRecord { _field1 :: String, _field2 :: Int, _field3 :: Bool
}
$(mkLabels [''MyRecord])
modifyThree f g h = modL field1 f
. modL field2 g
. modL field3 h
-chris
On 11 sep 2010, at 19:21, Jonathan Geddes wrote:
I know that record updates is a topic that has become a bit of a dead
horse, but here I go anyway:
I find that most of the record updates I read and write take the form
someUpdate :: MyRecord - MyRecord
someUpdate myRecord = myRecord
{ field1 = f $ field1 myRecord
, field2 = g $ field2 myRecord
, field3 = h $ filed3 myRecord
}
I find myself wishing I could write something more like
someUpdate :: MyRecord - MyRecord
someUpdate myRecord = myRecord
{ field1 = f
, field2 = g
, field3 = h
}
with equivalent semantics. Here = reads is transformed by. Operator
= could still be used for assignment as in current record updates.
The best part about such an extension, in my opinion, is that it would
open the door for anonymous lambda record updates. Something like:
someUpdate :: MyRecord - MyRecord
someUpdate = \{field1 = f, field2 = g, field3 = h}
again, with the same semantics. This becomes possible because you no
longer need to refer to the record within the {} part of the update.
This would be useful, for example, in the State monad. We could write:
someStateTransform :: State MyRecord ()
someStateTransform = do
modify $ \{field1 = (++!)}
...
where currently we see code like
someStateTransform :: State MyRecord ()
someStateTransform = do
modify $ \record-record{field1 = (++!) $ field1 record}
...
which repeats the record name 3 times and the field name twice. The
repetition just feels out of place next to all the other terse,
readable Haskell code in the program.
So what do my fellow haskellers think? Is this idea worth writing up a
proposal for?
Alternatively, can you offer me some advice on writing code in Haskell
2010 that avoids the ugly, repetitive style of record update?
--Jonathan
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Re: [Haskell-cafe] help me evangelize haskell.
On 5 sep 2010, at 09:28, Ben Lippmeier wrote: On 05/09/2010, at 2:38 AM, Michael Litchard wrote: I'll be starting a new job soon as systems tool guy. The shop is a perl shop as far as internal automation tasks go. But I am fortunate to not be working with bigots. If they see a better way, they'll take to it. So please give me your best arguments in favor of using haskell for task automation instead of perl, or awk or any of those scripting lanugages. Try to avoid religious arguments like by using Perl you're living in a state of sin, and focus on look how much easier it is to do X in Haskell. Grandiose, hand-wavy assertions like strong typing leads to shorter development times and more reliable software don't work on people that haven't already been there and done that. When you try to ram something down someone's throat they tend to resist. However, if you can provide something tasty and appealing they'll eat it themselves. Write a nice program, show it to your Perl programmer, and if they also think it's nice -- then you've already won. I've had success in situations with tight deadlines: the only way I got it done quickly and without bugs is by using Haskell (as opposed to PHP). Another place where you might have success is by writing a small compiler or interpreter for an internal language. Start small (in a niche, if you will) and expand upon that. -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Statically tracking validity - suggestions?
On 31 aug 2010, at 08:24, strejon wrote:
Hello. I'm using Haskell to write a specification for some software. The
software uses certificates (standard X.509 certificates) and stores user
name information in the Subject's CommonName field.
The X.509 standard doesn't actually require the presence of a CommonName
field so the contents of the Subject section (with the rest of the fields
omitted) are just represented by a Maybe User_Name.
import Data.List (find, concat)
import Data.Maybe (fromJust, isJust)
type User_Name= String
type Public_Key = Integer
data Subject_Name = Subject_Name (Maybe User_Name) deriving (Show, Eq)
data Certificate = Certificate {
certificate_subject :: Subject_Name,
certificate_key :: Public_Key,
certificate_issuer :: String,
certificate_serial :: Integer
} deriving (Show, Eq)
This is all well and good, but the problem is that the validity of
certificates isn't tracked statically and I have to use the following
as guards on all functions that only expect valid certificates (and
inevitably handle cases that I know can't actually happen but
have to be handled in pattern matching and the like, bloating
the specification):
user_name :: Subject_Name - Maybe User_Name
user_name (Subject_Name name) = name
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
I'm aware of phantom types and the like, but I've been unable to
work out how to use them (or another type system extension)
to properly track validity on the type level. I'd want something
like:
validate :: Certificate Possibly_Valid - Maybe (Certificate Valid)
With later functions only accepting values of type Certificate Valid.
Is there a simple way to do this?
Yes. Introduce a wrapper datatype, ValidCertificate. Create a module and export
only the wrapper datatype and a way to construct ValidCertificates in a safe
way:
module ValidateCertificate
( ValidCertificate,
fromValidCertificate,
createValidCertificate
) where
data ValidCertificate = ValidCertificate {fromValidCertificate :: Certificate}
createValidCertificate :: Certificate - Maybe ValidCertificate
createValidCertificate c | is_valid c = Just (ValidCertificate c)
| otherwise = Nothing
is_valid :: Certificate - Bool
is_valid = isJust . user_name . certificate_subject
The trick is not to export the constructor, but only a verified way to
construct values of ValidCertificate.
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Re: [Haskell-cafe] ANNOUNCE: DSTM 0.1.1
This looks very cool! It would be nice to put the pdf online somewhere, and add a link from the package documentation. Also, the chat client seems to have some problems with output buffering on my system (OS X, GHC 6.12). -chris On 3 aug 2010, at 10:35, Frank Kupke wrote: Hi, DSTM is an implementation of a robust distributed Software Transactional Memory (STM) library for Haskell. Many real-life applications are distributed by nature. Concurrent applications may profit from robustness added by re-implementation as distributed applications. DSTM extends the STM abstraction to distributed systems and presents an implementation efficient enough to be used in soft real-time applications. Further, the implemented library is robust in itself, offering the application developer a high abstraction level to realize robustness, hence, significantly simplifying this, in general, complex task. The DSTM package consists of the DSTM library, a name server application, and three sample distributed programs using the library. Provided are a simple Dining Philosophers, a Chat, and a soft real-time Bomberman game application. Distributed communication is transparent to the application programmer. The application designer uses a very simple name server mechanism to set up the system. The DSTM library includes the management of unavailable process nodes and provides the application with abstract error information thus facilitating the implementation of robust distributed application programs. For usage please look into the documentation file: DSTMManual.pdf. The package including the documentation can be found on: http://hackage.haskell.org/package/DSTM-0.1.1 Best regards, Frank Kupke ___ 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] Software architecture
I think the general process is the same. You define your components, try to decouple them as much as possible and implement them. One thing that is different from other languages: try to write as much pure code as possible. This is great for creating composable components. There are several different ways to structure your programs. The Utrecht Haskell Compiler is structured using attribute grammars, which is (similar to) aspect-oriented programming. Another architectural pattern you see a lot is that a program is provided as a library and a very small main function. A very good example of this is XMonad. You could also look at http://www.haskell.org/haskellwiki/Haskell_in_industry, which gives some pointers to commercial projects and how they are structured. -chris On 4 aug 2010, at 13:07, Charles-Pierre Astolfi wrote: Hey there, I'm searching for software designs in Haskell ; for example, I have a pretty good ideo of how I would arrange my modules/classes (in ocaml/(java/c++)) and how they would all fit together to create, say, a website aspirator. But I don't have any clue of the right way to do it with Haskell. I don't need a solution for this example, I'd just like to see how to manage non-trivial code. I haven't found any pointers on the interwebs. On an unrelated note, what is the simplest way to get the llvm bitcode? I understand I can compile myself ghc but it there an easier way? Thanks a lot! -- Cp ___ 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] [C Binding] Turning the mutable to immutable?
On 5 jul 2010, at 23:48, Yves Parès wrote: Hello, I don't know if some of you are familiar with the SFML library (stands for Simple and Fast Multimedia Library) -- http://sfml-dev.org As SDL, SFML is a 2D graphics library, but conversely to SDL it provides a hardware-accelerated drawing, through OpenGL. Well, I'm currently writing its Haskell binding, and I'm stuck with design issues. What I'm heading to is a full IO binding, and that's what I'd like to avoid. Have you considered writing a low-level binding and building a high-level library on top of that? -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] [C Binding] Turning the mutable to immutable?
I think it might influence performance, but it doesn't have to be that much. There are some optimization tricks you can apply to deal with this. Premature optimization is the root of all evil ;) -chris On 7 jul 2010, at 11:40, Yves Parès wrote: That's indeed an advice I've read [1]. But wouldn't it damage the performances, since code will have to go through an extra layer? [1] http://blog.ezyang.com/2010/06/principles-of-ffi-api-design 2010/7/7 Chris Eidhof ch...@eidhof.nl On 5 jul 2010, at 23:48, Yves Parès wrote: Hello, I don't know if some of you are familiar with the SFML library (stands for Simple and Fast Multimedia Library) -- http://sfml-dev.org As SDL, SFML is a 2D graphics library, but conversely to SDL it provides a hardware-accelerated drawing, through OpenGL. Well, I'm currently writing its Haskell binding, and I'm stuck with design issues. What I'm heading to is a full IO binding, and that's what I'd like to avoid. Have you considered writing a low-level binding and building a high-level library on top of that? -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] learning advanced haskell
On 14 jun 2010, at 07:42, Aran Donohue wrote: Hi Cafe, I've been doing Haskell for a few months, and I've written some mid-sized programs and many small ones. I've read lots of documentation and many papers, but I'm having difficulty making the jump into some of the advanced concepts I've read about. How do people build intuitions for things like RankNTypes and arrows? (Is the answer Get a PhD in type theory?) Normally I learn by coding up little exercise programs, but for these I don't have good intuitions about the kinds of toy problems I ought to try to solve that would lead me to understand these tools better. I learned my advanced stuff in two ways: 1. I followed excellent courses at Utrecht University, where they teach (among other things) advanced functional programming. 2. I just read a lot, which is a lot slower than 1. 3. By building my own programs, I inevitably find my self stuck and while searching for a solution, sometimes these concepts are the answer. For example, once I had a monadic program and I wanted to serialize/inspect the program, which turned out to be impossible in my case. The solution was to write it down using arrows (thus I had to learn arrows and also arrow-notatation). I think (for me) this is the most powerful way to learn new advanced concepts. I need practical problems to keep myself motivated. For systems like Template Haskell and SYB, I have difficulty judging when I should use Haskell's simpler built-in semantic abstractions like functions and typeclasses and when I should look to these other mechanisms. Sometimes Template Haskell or SYB is the answer, and it's a matter of style, but I try to avoid them as much as possible. I find that generic programming in the style of regular [1] or emgm [2] is often much simpler. Some more tips: subscribe to planet haskell, if you haven't done that already. Try to find ICFP/JFP/etc papers online that interest you. -chris [1]: http://hackage.haskell.org/package/regular [2]: http://hackage.haskell.org/package/emgm___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Steven S. Skiena of The Algorithm Design Manual, Second Edition, 2008 has sent me a message that if there is a Haskell page of algorithms he will link to it.
Nhe most important reference in literature might be Okasaki's Purely functional
data structures:
@book{okasaki1999purely,
title={{Purely functional data structures}},
author={Okasaki, C.},
year={1999},
publisher={Cambridge Univ Pr}
}
-chris
On 28 mei 2010, at 05:23, Casey Hawthorne wrote:
Hi:
Steven S. Skiena of The Algorithm Design Manual, Second Edition,
2008 has sent me a message that if there is a Haskell page of
algorithms he will link to it.
So, is there such a page and/or is there some collection(s) of
algorithms and data structures some where that I can massage into the
shape of his book?
:)
--
Regards,
Casey
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Re: [Haskell-cafe] [ANNOUNCE] First Public Release of the Snap Framework
Awesome! Congratulations on the first release, I look forward to working with it. Also, the web design is great, possibly the best designed Haskell library website I've seen so far. -chris On 22 mei 2010, at 07:25, Gregory Collins wrote: Hello all, To coincide with Hac Phi 2010 (http://www.haskell.org/haskellwiki/Hac_%CF%86), the Snap team is happy to announce the first public release of the Snap Framework, a simple and fast Haskell web programming server and library for unix systems. For installation instructions, documentation, and more information, see our website at http://snapframework.com/. Snap is well-documented and has a test suite with a high level of code coverage, but it is early-stage software with still-evolving interfaces. Snap is therefore most likely to be of interest to early adopters and potential contributors. Snap is BSD-licensed and currently only runs on Unix platforms; it has been developed and tested on Linux and Mac OSX Snow Leopard. Snap Features: * A simple and clean monad for web programming, similar to happstack's but simpler. * A *fast* HTTP server library with an optional high-concurrency backend (using libev). * An XML-based templating system for generating xhtml that allows you to bind Haskell functionality to XML tags in your templates. * Some useful utilities for web handlers, including gzip compression and fileServe. * Iteratee-based I/O, allowing composable streaming in O(1) space without any of the unpredictable consequences of lazy I/O. If you have questions or comments, please contact us on our mailing list (http://mailman-mail5.webfaction.com/listinfo/snap) or in the #snapframework channel on the freenode IRC network. Cheers, G -- Gregory Collins g...@gregorycollins.net ___ 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] cabal problem on OS X
I have a different problem (also after doing a cabal update): I get a bus error. I just created this ticket for it: http://hackage.haskell.org/trac/hackage/ticket/691 -chris On 22 mei 2010, at 13:20, Bill Atkins wrote: When I run cabal update on my Mac (Snow Leopard, Intel), I get: % cabal update Downloading the latest package list from hackage.haskell.org cabal: Codec.Compression.Zlib: incompatible zlib version Anyone else seeing this? Reinstalling the Haskell Platform hasn't helped. Thanks! ___ 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] polyvariadic function for Applicative instances
Maybe this is what you are looking for: http://www.haskell.org/haskellwiki/Idiom_brackets -chris On 9 mei 2010, at 18:39, Xiao-Yong Jin wrote: Hi, Is it possible to have a function accept variable number of arguments, such that 'f' can be instantiated to different concrete types as f :: Applicative a = (e1 - f) - a e1 - A f f g a = pure g * a f :: Applicative a = (e1 - e2 - f) - a e1 - a e2 - A f f g a b = pure g * a * b Thanks, Xiao-Yong -- Jc/*__o/* X\ * (__ Y*/\ ___ 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] How efficient is read?
There is the ChristmasTree package (http://hackage.haskell.org/package/ChristmasTree) which provides a very fast read alternative by deriving grammars for each datatype. If you want to know the speed differences, see http://www.cs.uu.nl/wiki/bin/view/Center/TTTAS for more information (it's in the Haskell Do You Read Me paper, see section 5 for a comparison of efficiency). -chris On 9 mei 2010, at 05:32, Tom Hawkins wrote: I have a lot of structured data in a program written in a different language, which I would like to read in and analyze with Haskell. And I'm free to format this data in any shape or form from the other language. Could I define a Haskell type for this data that derives the default Read, then simply print out Haskell code from the program and 'read' it in? Would this be horribly inefficient? It would save me some time of writing a parser. -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] Re: lhs2TeX - lhs2TeX.fmt missing
I've generated large LaTeX documents with several modules without too much hassle. The key was to use %include a lot, as well as conditionals. Lots of %if False around import statements. -chris On 5 mei 2010, at 20:18, Pierre-Etienne Meunier wrote: By the way, if someone on this list has got too much time, he could write something that would fulfill the goals of literate programming -- à la web and cweb. Knuth was able to make books with his source code. I believe that lhs2tex is great for classes about haskell or fp, but I never found it satisfying for programs with several modules, for instance. El 05/05/2010, a las 12:42, Ozgur Akgun escribió: OK, I've found them! They were under /Users/username/.cabal/share/lhs2tex-1.15 and this path was not in the search path of lhs2TeX. I'm using Snow Leoprad. This might be a bug I guess? Anyway, problem solved for me. Best, On 5 May 2010 16:03, Ozgur Akgun ozgurak...@gmail.com wrote: Hi all, I am trying to get lhs2TeX to work. I installed the package using cabal, and now I try to run it on a very simple *.lhs file. But it blames me and says user error, cannot find lhs2TeX.fmt: lhs2TeX: user error (File `lhs2TeX.fmt' not found in search path: And, when I check the search path, there really is no lhs2TeX.fmt file. Should I download it separately or something like that? PS: Thanks for the great package to the authors! Best, Ozgur Akgun -- Ozgur Akgun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Cabal-install: bus error
Hey everyone, After I upgraded to a newer cabal-install my cabal-install broke again: I get a Bus Error when doing cabal update or cabal install something. The version that was bundled with the Haskell platform worked fine, but now it's broken again. I'm not sure what it was that went wrong or how to debug this. The previous time I had Bus Errors I upgraded to the newest available Haskell Platform release and started from scratch. I would prefer not to do that again. However, I don't really know how to solve the Bus Error. Does anyone have a clue where to start? Or is there a way to undo my cabal-install upgrade? -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: FRP for game programming / artifical life simulation
I agree. This would be an extremely useful feature, not only for game development, but also for web development. We often use continuations as a way to add state to the web, but this fails for two reasons: whenever the server restarts, or when we scale to multiple machines. However, I think it is not easy to do this: traversing the heap should be relatively simple, however: what if a function implementation changes? An interesting approach is taken by the Clean guys: they use dynamics, which can store a function, a type representation and the heap to disk. See also this old thread: http://www.mail-archive.com/haskell-cafe@haskell.org/msg34054.html -chris On 28 apr 2010, at 19:50, Peter Verswyvelen wrote: Interesting topic. I find it a bit annoying that Haskell doesn't provide support to save functions. I understand this is problematic, but it would be very nice if the Haskell runtime provided a way to serialize (part of) the heap, making sure that pointers to compiled functions get resolved correctly. On Wed, Apr 28, 2010 at 6:42 PM, Christopher Lane Hinson l...@downstairspeople.org wrote: On Wed, 28 Apr 2010, Ben wrote: I want to save the state of the system to disk, I want to be able to play the game, pick a point to stop, freeze it and turn off the computer, and then come back later and resume. Why is that unwise? What are the alternatives? B On Tue, 27 Apr 2010, Ben wrote: slightly off topic, but how does one handle pausing / saving / restarting in the FRP framework, especially the arrowized version? If we're about Arrow FRP, remember that the arrow typeclass includes a function, 'arr', that admits any function as a parameter, and these are in general impossible to serialize to disk. Since Arrow FRP ends up roughly in a form of: FRP a b c = a b (c, FRP a b c), an Arrow instance is actually the state of the system. There are a few tactics that would get us around this limitation, but they are rather severe. You could render 'arr' useless in several ways, or you could save all the input to a system and replay it. But I would argue that even if you wanted to do this, saving an FRP system is, to me, like saving a system in the IO monad, (which, there are tactics that would let you do this, too). It's probablematic in part because the FRP system probably has active hooks into the user interface, such as windows and other widgits that it owns, and possibly other devices (such as physical rocket engines). Even if the FRP system is completely pure and can be referenced by a single pointer, it is easily and rightfully aware of specific details of the hardware it is embedded in. So it seems to me that what we actually want, to do complex simulations with persistance, is not an FRP system that interacts with the outside world, but a self-contained, self-interacting, differential equation hairball. Such a system would be very cool, but I think that the numerical algorithms needed exceed what an FRP system should try to provide. Friendly, --Lane ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] GSOC idea: Haskell JVM bytecode library
We've used this library to generate a prototype JVM backend for UHC about a year ago, and it Just Worked. That was probably on 6.10 or 6.8. -chris On 26 mrt 2010, at 21:33, Brian Alliet wrote: On Fri, Mar 26, 2010 at 08:01:57PM +, Alexandru Scvortov wrote: I'm thinking of writing a library for analyzing/generating/manipulating JVM bytecode. To be clear, this library would allow one to load and work with JVM classfiles; it wouldn't be a compiler, interpretor or a GHC backend. I wrote a JVM classfile library as part of LambdaVM (which is actually a JVM backend for GHC, it is a bit bit-rotted though, I need to get back into it): http://darcs.brianweb.net/hsjava/ It requires my hsutils library (also available on darcs.brianweb.net). I haven't touched the code in a while and it might need a tweak or two with recent GHC versions. Drop me a line if you have any trouble getting it working (and patches are certainly welcome). There isn't much documentation, besides the code and a few example programs that dump a pretty printed version of the data structure. I'd be more than happy to give anybody who is interested in using it some pointers though. -Brian ___ 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] GSOC idea: Haskell JVM bytecode library
On 26 mrt 2010, at 22:37, Alexandru Scvortov wrote: How stable is it? I don't know. I remember that we didn't have to change anything and that everything just worked. Was it easy to use? Actually yes, because: Did it have enough documentation? I think we used the Java documentation. The nice thing about the hsjava library is that it provides datatypes that closely match assembly. Do you think it could use a rewrite? If so, what should be done differently? Could it be extended into something more? I guess it could be double-checked and released on hackage. Maybe add tail-call support to the library? (sorry for the barrage of questions, but you're the one person I've seen so far, apart from the original programmer, that has experience with this) Only very little experience. It was a project of a couple of weeks. -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] derivable type classes
No. A solution for this (depending on the type class you want to derive) is Generic Programming. Using Generic Programming, you can define functions that work on the structure of the type. For example, take a look at the regular package [1]. It provides all the functionality to write your own generic functions. -chris [1]: http://hackage.haskell.org/package/regular On 23 mrt 2010, at 11:52, Ozgur Akgun wrote: Can a user define a derivable type class of her own? If yes, how? Cheers, -- Ozgur Akgun ___ 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] ANN: Salvia-1.0.0
On 23 mrt 2010, at 14:27, Bas van Dijk wrote: On Tue, Mar 23, 2010 at 2:13 PM, Sebastiaan Visser sfvis...@cs.uu.nl wrote: Nice! This is certainly worth it. BTW What's the git equivalent of 'darcs send -o filename' which saves the patches to filename? I would rather send my patches as email attachements instead of copying my repository to my webserver. (Note this is the first time I used git) The way I like to work is forking the repository on github (you need an account for that, though). Then you can push the changes to your forked repository and the original author will see it. Have a look at http://book.git-scm.com/5_git_and_email.html to see how you can send changes by email. -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] ANN: regular-web 0.1 | generic web programming in Haskell
From the ZuriHac hackathon, I am happy to announce the first release of the regular-web package [1]. The package contains functions for generic web programming: generating HTML, JSON and Formlets. It is based on the regular generic programming library [2]. Generic HTML and forms are often not sufficient for real purposes, so we encourage the use of regular-web in combination with the fclabels package [3]. There is an example in the documentation of the Formlets module. Furthermore, there is a slightly larger example [4] on github that shows off some more features of the package. This is a preliminary release and the API will probably change. I am interested to see what other people think of this. So please send me your comments or fork the project on github. [1]: http://hackage.haskell.org/package/regular-web [2]: http://hackage.haskell.org/package/regular [3]: http://hackage.haskell.org/package/fclabels [4]: http://github.com/chriseidhof/regular-web/blob/master/Example.lhs ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Code that doesn't compile - but should :)
What about this?
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies, FlexibleInstances,
UndecidableInstances, FlexibleContexts, EmptyDataDecls, ScopedTypeVariables,
TypeOperators, TypeSynonymInstances #-}
data Data k = Pair Integer (() - k)
data RecData = RecData (Data RecData)
mk_data x = RecData(Pair x (\() - mk_data (x+1)))
The I had to change the type of the Converter typeclass
class Converter a f where convert :: f a - a
-- instance Converter RecData Data where
-- convert (RecData r) = r
class Selector s a where select :: s - a
And explicitly quantify the type variables:
f :: forall f s a . (Selector s (a-f a), Converter a f) = s - (a-a)
f s =
let method = select s :: a - f a
in (\x -
let res = method x
in convert res)
-chris
On 16 mrt 2010, at 10:36, Giuseppe Maggiore wrote:
The error message (obtained by loading the file with ghci) is:
GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main (
C:\Users\pulcy\Desktop\Papers\Monads\Objec
tiveMonad\HObject\Experiments\FunctorsProblems.hs, interpreted )
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Experiments\Functors
Problems.hs:18:15:
Could not deduce (Selector s (f a - a))
from the context (Selector s (a1 - f1 a1), Converter a1 f1)
arising from a use of `select'
at
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObjec
t\Experiments\FunctorsProblems.hs:18:15-22
Possible fix:
add (Selector s (f a - a)) to the context of
the type signature for `f'
or add an instance declaration for (Selector s (f a - a))
In the expression: select s
In the definition of `method': method = select s
In the expression:
let method = select s in (\ x - let res = ... in convert res)
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Experiments\Functors
Problems.hs:21:11:
Couldn't match expected type `a1' against inferred type `f a'
`a1' is a rigid type variable bound by
the type signature for `f'
at
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Expe
riments\FunctorsProblems.hs:16:18
In the expression: convert res
In the expression: let res = method x in convert res
In the expression: (\ x - let res = method x in convert res)
Failed, modules loaded: none.
Prelude
On Tue, Mar 16, 2010 at 2:31 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
Giuseppe Maggiore giuseppe...@gmail.com writes:
Hi! Can anyone tell me why this code does not work? I cannot seem to
figure why it is broken...
The error message (and how you got it) would help...
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances,
UndecidableInstances, FlexibleContexts, EmptyDataDecls,
ScopedTypeVariables,
TypeOperators, TypeSynonymInstances #-}
You sure you have enough language extensions there? ;-)
Barely :)
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
--
Giuseppe Maggiore
Ph.D. Student (Languages and Games)
Microsoft Student Partner
Mobile: +393319040031
Office: +390412348444
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Re: [Haskell-cafe] Code that doesn't compile - but should :)
On 16 mrt 2010, at 10:58, Giuseppe Maggiore wrote:
Well, first of all thanks!
Second, why the need for explicit quantification?
I'm not sure, but I think it has to do with ambiguity. I think it's similar to
the problem:
readShow :: (Read a, Show a) - String - String
readShow = show . read
We need to explicitly quantify over the type variables so that we can give an
explicit type signature on the following line:
let method = select s :: a - f a
There might be an easier way to do this, but I'm not sure how exactly.
-chris
On Tue, Mar 16, 2010 at 2:39 AM, Chris Eidhof ch...@eidhof.nl wrote:
What about this?
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances,
UndecidableInstances, FlexibleContexts, EmptyDataDecls,
ScopedTypeVariables,
TypeOperators, TypeSynonymInstances #-}
data Data k = Pair Integer (() - k)
data RecData = RecData (Data RecData)
mk_data x = RecData(Pair x (\() - mk_data (x+1)))
The I had to change the type of the Converter typeclass
class Converter a f where convert :: f a - a
-- instance Converter RecData Data where
-- convert (RecData r) = r
class Selector s a where select :: s - a
And explicitly quantify the type variables:
f :: forall f s a . (Selector s (a-f a), Converter a f) = s - (a-a)
f s =
let method = select s :: a - f a
in (\x -
let res = method x
in convert res)
-chris
On 16 mrt 2010, at 10:36, Giuseppe Maggiore wrote:
The error message (obtained by loading the file with ghci) is:
GHCi, version 6.10.4: http://www.haskell.org/ghc/ :? for help
Loading package ghc-prim ... linking ... done.
Loading package integer ... linking ... done.
Loading package base ... linking ... done.
[1 of 1] Compiling Main (
C:\Users\pulcy\Desktop\Papers\Monads\Objec
tiveMonad\HObject\Experiments\FunctorsProblems.hs, interpreted )
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Experiments\Functors
Problems.hs:18:15:
Could not deduce (Selector s (f a - a))
from the context (Selector s (a1 - f1 a1), Converter a1 f1)
arising from a use of `select'
at
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObjec
t\Experiments\FunctorsProblems.hs:18:15-22
Possible fix:
add (Selector s (f a - a)) to the context of
the type signature for `f'
or add an instance declaration for (Selector s (f a - a))
In the expression: select s
In the definition of `method': method = select s
In the expression:
let method = select s in (\ x - let res = ... in convert res)
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Experiments\Functors
Problems.hs:21:11:
Couldn't match expected type `a1' against inferred type `f a'
`a1' is a rigid type variable bound by
the type signature for `f'
at
C:\Users\pulcy\Desktop\Papers\Monads\ObjectiveMonad\HObject\Expe
riments\FunctorsProblems.hs:16:18
In the expression: convert res
In the expression: let res = method x in convert res
In the expression: (\ x - let res = method x in convert res)
Failed, modules loaded: none.
Prelude
On Tue, Mar 16, 2010 at 2:31 AM, Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com wrote:
Giuseppe Maggiore giuseppe...@gmail.com writes:
Hi! Can anyone tell me why this code does not work? I cannot seem to
figure why it is broken...
The error message (and how you got it) would help...
{-# LANGUAGE MultiParamTypeClasses, FunctionalDependencies,
FlexibleInstances,
UndecidableInstances, FlexibleContexts, EmptyDataDecls,
ScopedTypeVariables,
TypeOperators, TypeSynonymInstances #-}
You sure you have enough language extensions there? ;-)
Barely :)
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
IvanMiljenovic.wordpress.com
--
Giuseppe Maggiore
Ph.D. Student (Languages and Games)
Microsoft Student Partner
Mobile: +393319040031
Office: +390412348444
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Ph.D. Student (Languages and Games)
Microsoft Student Partner
Mobile: +393319040031
Office: +390412348444
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Re: [Haskell-cafe] references for compiler optimizations for functional languages
I'd like to add Urban Boquist's thesis to that list: http://www.cs.chalmers.se/~boquist/phd/index.html (I've added it to the wiki page as well). -chris On 1 mrt 2010, at 22:26, Don Stewart wrote: mvanier42: Hi everyone, I'm interested in collecting good references for compiler optimizations for functional languages (lazy, strict, statically-typed or not). Any suggestions? There's lots for what GHC implements on SimonPJ's site: http://www.research.microsoft.com/~simonpj/Papers/inlining/index.htm http://research.microsoft.com/en-us/um/people/simonpj/papers/cpr/index.htm http://research.microsoft.com/en-us/um/people/simonpj/papers/usage-types/usage.htm http://research.microsoft.com/en-us/um/people/simonpj/papers/comp-by-trans-scp.ps.gz http://research.microsoft.com/en-us/um/people/simonpj/papers/andy-thesis.ps.gz http://research.microsoft.com/en-us/um/people/simonpj/papers/deforestation-short-cut.ps.Z http://www.cse.unsw.edu.au/~dons/papers/CLS07.html :) I've collected many of them here: http://haskell.org/haskellwiki/Research_papers/Compilation#Compiler_Analyses -- Don ___ 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] using haskell to serve with apache
We run a couple of Happstack processes with FastCGI, and it works like a charm. We even wrote a module for it: http://hackage.haskell.org/package/happstack-fastcgi -chris On 1 mrt 2010, at 20:19, Yitzchak Gale wrote: brad clawsie wrote: should i just try out something based on fastcgi? Obviously it depends on exactly what you want to do. For a simple very low volume page, even cgi should be just fine. I use it all the time. Regards, Yitz ___ 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] Two GET HTTP requests
Hi nwn,
I had the following error:
Run: Network/Socket/Internal.hsc:(298,2)-(314,60): Non-exhaustive patterns in
case. The code for those lines look like this:
peekSockAddr p = do
family - (#peek struct sockaddr, sa_family) p
case family :: CSaFamily of
#if defined(DOMAIN_SOCKET_SUPPORT)
(#const AF_UNIX) - do
str - peekCString ((#ptr struct sockaddr_un, sun_path) p)
return (SockAddrUnix str)
#endif
(#const AF_INET) - do
addr - (#peek struct sockaddr_in, sin_addr) p
port - (#peek struct sockaddr_in, sin_port) p
return (SockAddrInet (PortNum port) addr)
#if defined(IPV6_SOCKET_SUPPORT)
(#const AF_INET6) - do
port - (#peek struct sockaddr_in6, sin6_port) p
flow - (#peek struct sockaddr_in6, sin6_flowinfo) p
addr - (#peek struct sockaddr_in6, sin6_addr) p
scope - (#peek struct sockaddr_in6, sin6_scope_id) p
return (SockAddrInet6 (PortNum port) flow addr scope)
#endif
Thanks for all your help. I'll first upgrade to a new GHC and then try again.
-chris
On 9 feb 2010, at 06:41, Yusaku Hashimoto wrote:
Try to reinstall HTTP package also. I think your HTTP package is still
linked with old broken network package.
HTTP depends on network. And network is a binding for network API of
OS. These API is for C-language. When ghc builds such binding
packages, It runs gcc for some purpose. gcc thinks you need 64bit
binary (from SL, I believe.) and works for 64bit environment. But ghc
on Mac can only build 32bit binaries. So it causes the problem.
You can check if network package was correctly built by running this.
This takes a host name, and gets the root document of the host via
HTTP using a socket. Build and try `./this_program haskell.org`
import Network.Socket
import System.IO
import System.Environment
getAddr :: HostName - IO AddrInfo
getAddr host = head `fmap`
(getAddrInfo (Just defaultHints { addrSocketType = Stream })
(Just host)
(Just http))
connected :: HostName - IO Socket
connected host = do
addrinfo - getAddr host
sock - socket (addrFamily addrinfo)
(addrSocketType addrinfo)
(addrProtocol addrinfo)
connect sock (addrAddress addrinfo)
return sock
httpGet :: HostName - IO String
httpGet host = do
h - flip socketToHandle ReadWriteMode = connected host
hSetBuffering h NoBuffering
hPutStr h GET / HTTP/1.0\r\n\r\n
hGetContents h
main = fmap head getArgs = httpGet = putStr
I should have mentioned them in my last mail. Sorry.
By the way, ghc-6.12 on Mac still can not build 64bit binaries. So
upgrading ghc won't solve it.
--nwn
On Mon, Feb 8, 2010 at 12:50 AM, Chris Eidhof ch...@eidhof.nl wrote:
Thanks. Unfortunately, it didn't help. The thing that frustrates me is that
it's quite hard to debug. I guess I'll upgrade my GHC to 6.12, hopefully
that'll solve it.
-chris
On 7 feb 2010, at 16:07, Yusaku Hashimoto wrote:
Hello,
On Sat, Feb 6, 2010 at 2:51 AM, Chris Eidhof ch...@eidhof.nl wrote:
Approach 3: I used the simpleHTTP function from the HTTP package. This
crashed, after I dug a little deeper into the code, it threw an error on
calling the parseURI function (openFile: no such file exists). I installed
the latest network package and upgraded my HTTP package, and the parseURI
error went away. I felt like I was almost there, and tried the following:
simpleHTTP (getRequest http://haskell.org;)
This failed with just the text Bus error. I searched the HTTPBis git
repository, but couldn't find the text Bus error. I don't have a clue of
how to fix this.
Try reinstall network package with `cabal install --reinstall
--hsc2hs-options=--cflag=-m32 --lflag=-m32`.
See also: http://hackage.haskell.org/trac/ghc/ticket/3681
Hope this helps.
--nwn
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Re: [Haskell-cafe] Lazy language on JVM/CLR
I don't think it's pure. I would definitely use a pure language on the JVM, but IIRC Open Quark / Cal is an impure language. For example, from the library documentation: printLine :: String - (). -chris On 9 feb 2010, at 15:31, Tim Wawrzynczak wrote: Perhaps this is similar to what you're looking for. http://openquark.org/Open_Quark/Welcome.html It's a pure, lazy language for the JVM. I haven't used it myself, but I would imagine that it would have a Java FFI. Cheers, - Tim On Mon, Feb 8, 2010 at 6:42 PM, Tony Morris tonymor...@gmail.com wrote: I have hypothesised a pure, lazy language on the JVM and perhaps the .NET CLR with FFI to .NET/Java libraries. I foresee various problems but none that are catastrophic; just often requiring a compromises, sometimes very unattractive compromises. I have authored several libraries in the same vain as pure, lazy programming to run on the JVM in Java and Scala programming languages. I expect others have forethought and perhaps even experimented with such a language. Are there any dangers to be wary of that undo the entire endeavour? Thanks for any insights. -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Two GET HTTP requests
On 7 feb 2010, at 19:52, Lars Viklund wrote: On Sun, Feb 07, 2010 at 05:12:23PM +, Ben Millwood wrote: This failed with just the text Bus error. I searched the HTTPBis git repository, but couldn't find the text Bus error. I don't have a clue of how to fix this. Bus error is a message generated by the operating system. On OS X, it can mean a null dereference, which is very unusual. You did not mention whether the machine running your OS X was a PowerPC or an Intel machine. On non-x86 platforms, a bus error is usually caused by misaligned memory accesses. Unlike the x86 which silently and expensively fixes any misaligned accesses, sane processors kick and scream, resulting in a bus error. Such things tend to happen quite often when development of a software mainly takes place on x86 family chips, and are revealed when some poor soul on an UltraSparcIII tries to run them. I'm on X86, Snow Leopard. I'm running GHC 6.10.2. -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Two GET HTTP requests
I should add that I was able to work around the issue by using Michael Snoyman's http-wget [1] package. It uses the command-line version of wget, which does work on my machine. -chris [1]: http://hackage.haskell.org/package/http-wget On 7 feb 2010, at 16:50, Chris Eidhof wrote: Thanks. Unfortunately, it didn't help. The thing that frustrates me is that it's quite hard to debug. I guess I'll upgrade my GHC to 6.12, hopefully that'll solve it. -chris On 7 feb 2010, at 16:07, Yusaku Hashimoto wrote: Hello, On Sat, Feb 6, 2010 at 2:51 AM, Chris Eidhof ch...@eidhof.nl wrote: Approach 3: I used the simpleHTTP function from the HTTP package. This crashed, after I dug a little deeper into the code, it threw an error on calling the parseURI function (openFile: no such file exists). I installed the latest network package and upgraded my HTTP package, and the parseURI error went away. I felt like I was almost there, and tried the following: simpleHTTP (getRequest http://haskell.org;) This failed with just the text Bus error. I searched the HTTPBis git repository, but couldn't find the text Bus error. I don't have a clue of how to fix this. Try reinstall network package with `cabal install --reinstall --hsc2hs-options=--cflag=-m32 --lflag=-m32`. See also: http://hackage.haskell.org/trac/ghc/ticket/3681 Hope this helps. --nwn ___ 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] Two GET HTTP requests
Thanks. Unfortunately, it didn't help. The thing that frustrates me is that it's quite hard to debug. I guess I'll upgrade my GHC to 6.12, hopefully that'll solve it. -chris On 7 feb 2010, at 16:07, Yusaku Hashimoto wrote: Hello, On Sat, Feb 6, 2010 at 2:51 AM, Chris Eidhof ch...@eidhof.nl wrote: Approach 3: I used the simpleHTTP function from the HTTP package. This crashed, after I dug a little deeper into the code, it threw an error on calling the parseURI function (openFile: no such file exists). I installed the latest network package and upgraded my HTTP package, and the parseURI error went away. I felt like I was almost there, and tried the following: simpleHTTP (getRequest http://haskell.org;) This failed with just the text Bus error. I searched the HTTPBis git repository, but couldn't find the text Bus error. I don't have a clue of how to fix this. Try reinstall network package with `cabal install --reinstall --hsc2hs-options=--cflag=-m32 --lflag=-m32`. See also: http://hackage.haskell.org/trac/ghc/ticket/3681 Hope this helps. --nwn ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Two GET HTTP requests
Hi everyone, I'm trying to do a number of successive HTTP requests in one program. Here's what I tried: Approach 1: I used the 'download' package, which failed to install on OS X. It fails with error: libio.h: No such file or directory. Approach 2: I installed the 'download-curl' package, and tried again. This seems to fail on the following example: import Network.Curl.Download main = do x - openURI http://haskell.org; y - openURI http://haskell.org/hoogle; return () If I put a print statement around the second line of the do-statement it looks like openURI never returns. Approach 3: I used the simpleHTTP function from the HTTP package. This crashed, after I dug a little deeper into the code, it threw an error on calling the parseURI function (openFile: no such file exists). I installed the latest network package and upgraded my HTTP package, and the parseURI error went away. I felt like I was almost there, and tried the following: simpleHTTP (getRequest http://haskell.org;) This failed with just the text Bus error. I searched the HTTPBis git repository, but couldn't find the text Bus error. I don't have a clue of how to fix this. I'm a bit stuck here, I would love to help fix the errors, but don't know what would be the best place to begin. If anyone can point me in the right direction, I will try to patch at least one of these packages. Thanks, -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Determining application directory
Hi Matveev, You might be interested in the System.Directory module: http://hackage.haskell.org/packages/archive/directory/1.0.0.3/doc/html/System-Directory.html HTH, -chris On 27 jan 2010, at 18:06, Matveev Vladimir wrote: Hi, I'm writing cross-platform application in Haskell which should be running under Windows and Linux. Under Linux configuration is stored in the /etc directory, and under Windows configuration is meant to be in the application directory. So, is there a way to get an application directory path under Windows? I remember that there is a way to do this using WinAPI, but how to do this Haskell? ___ 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] HTML - based GUIs - follow up
Formlets themselves don't require a server. You can use them from the commandline. However, formlets do have a limitation: they are not interactive. I would really like a library that does something like formlets (compositional web forms) but with a FRP-style of writing. A contrived example: Suppose I have a page with a label that displays a number, and a slider. When I change the slider, the number in the label has to change accordingly. The example above is currently not possible with formlets. -chris On 20 jan 2010, at 18:30, Colin Paul Adams wrote: Günther == Günther Schmidt gue.schm...@web.de writes: Günther My question is: do formlets only work server based or is it Günther also possible to use formlet sans happs? Yes (I think) and yes. -- Colin Adams Preston Lancashire ___ 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] Compiling a shared library on MacOS X
I'm not sure if it is of any help, but at the haskell-wiki there's an article about how to communicate between Haskell and Objective-C using XCode: http://haskell.org/haskellwiki/Using_Haskell_in_an_Xcode_Cocoa_project -chris On 4 jan 2010, at 00:36, Ivan Miljenovic wrote: If I recall correctly, dynamic linking/shared library support is not yet available for OSX, as the Industrial Haskell Group does not have any knowledge of OSX (but is willing to pay someone who does to do the work). 2010/1/4 Jean-Denis Koeck jdko...@gmail.com: Hello, I'm using the following cabal file to build a shared library with ghc: Build-Type:Simple Executable libmylibrary.dll If os(windows) CPP-Options:-DWIN32 Extensions: ForeignFunctionInterface Build-Depends:... Main-Is: libmylibrary.hs Ghc-Options: -W --make -no-hs-main -optl-shared -optl-s -O2 The resulting library is called from a C++ graphical user interface (using Qt), which worked great so far on Windows and Linux. However, the compilation fails on MacOS X: Undefined symbols: _ZCMain_main_closure, referenced from: _ZCMain_main_closure$non_lazy_ptr in libHSrts.a(Main.o) ___stginit_ZCMain, referenced from: ___stginit_ZCMain$non_lazy_ptr in libHSrts.a(Main.o) ld: symbol(s) not found collect2: ld returned 1 exit status I don't know much about shared libraries, even less about them on MacOS X :( Any idea ? Jean-Denis Koeck ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Ivan Lazar Miljenovic ivan.miljeno...@gmail.com IvanMiljenovic.wordpress.com Joan Crawford - I, Joan Crawford, I believe in the dollar. Everything I earn, I spend. - http://www.brainyquote.com/quotes/authors/j/joan_crawford.html ___ 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] diff implementation in haskell
Also, there is a paper about doing a type-safe diff in Agda, http://portal.acm.org/citation.cfm?id=1596614.1596624 I heard rumors that the library will be ported to Haskell. -chris On 8 dec 2009, at 15:20, Bayley, Alistair wrote: From: haskell-cafe-boun...@haskell.org [mailto:haskell-cafe-boun...@haskell.org] On Behalf Of Ketil Malde Don Stewart d...@galois.com writes: http://hackage.haskell.org/package/Diff Wherein we can read: | This is an implementation of the O(ND) diff algorithm [...]. It is O(mn) | in space. At first I thought 'N' and 'M' would be the lengths of the lists, and 'D' is the number of differences, but then the space bound doesn't make sense. I tried to find the reference, but Citeseer is down (again. sigh). Anybody know what the bounds really are? I think the space bounds are O(M+N). Section 4b. A Linear Space Refinement concludes with Unfortunately, the input sequences A and B must be kept in memory, implying that a total of O(M+N) space is needed. BTW, there is a minor improvement to this algorithm (claims to be faster, same space usage): http://research.janelia.org/myers/Papers/np_diff.pdf found via: http://scholar.google.com/scholar?q=%22An+O(NP)+Sequence+Comparison+Algo rithm.%22 I thought this paper was easier to understand. Alistair * Confidentiality Note: The information contained in this message, and any attachments, may contain confidential and/or privileged material. It is intended solely for the person(s) or entity to which it is addressed. Any review, retransmission, dissemination, or taking of any action in reliance upon this information by persons or entities other than the intended recipient(s) is prohibited. If you received this in error, please contact the sender and delete the material from any computer. * ___ 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] Bulding a library for C users on OS X
On 2 nov 2009, at 03:30, Manuel M T Chakravarty wrote: Chris Eidhof: I'm trying to call a Haskell function from C, on OS X. There's an excellent post [1] by Tomáš Janoušek that explains how to do this on Linux. However, on OS X, it's different. First of all, it looks like the -no-hs-main flag is ignored, because I get the following error: ghc -O2 --make -no-hs-main -optl '-shared' -optc '- DMODULE=Test' -o Test.so Test.hs module_init.c [1 of 1] Compiling Main ( Test.hs, Test.o ) Test.hs:1:0: The function `main' is not defined in module `Main''' The flag -no-hs-main is a link-time flag that allows you to link without a main function, but you are getting a compile time error. It's as if you try to export main, but don't define it. Have you had a look at http://www.haskell.org/ghc/docs/latest/html/users_guide/ffi-ghc.html#foreign-export-ghc ? Interesting! I didn't see that section before, thanks a lot. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [solved] Re: [Haskell-cafe] Calling Haskell from C, Linking with gcc?
I can confirm that, if you follow the steps on the wiki, you'll end up with a working Mac application. Excellent work John, thanks very much! -chris On 30 okt 2009, at 00:53, John Velman wrote: It's taken 21 days with interruptions, but I finally posted a tutorial with details of what I did on the Haskel Wiki. Category:Tutorials, title: Using Haskell in an Xcode Cocoa project Hope it's clear. Please send comments and suggestions. John V. On Thu, Oct 08, 2009 at 10:34:07AM +0200, Wouter Swierstra wrote: On 7 Oct 2009, at 23:39, John Velman wrote: For anyone following this: The XCode ld script is complex, and has mac specific defaults early in the search path specification, and I probably don't want to change these. A library in a default path is the wrong libgmp.[dylib | a]. Is there any chance you'll write up exactly what you needed to do on a blog/TMR article/Haskell wiki page? I've tried doing something similar, ran into linking problems, and gave up my fight with XCode. I think this would be a really useful resource for both Obj-C programmers looking into Haskell and Haskell programmers who want to have a fancy Cocoa GUI. Thanks! Wouter ___ 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] Bulding a library for C users on OS X
Hey all, I'm trying to call a Haskell function from C, on OS X. There's an excellent post [1] by Tomáš Janoušek that explains how to do this on Linux. However, on OS X, it's different. First of all, it looks like the -no-hs-main flag is ignored, because I get the following error: ghc -O2 --make -no-hs-main -optl '-shared' -optc '- DMODULE=Test' -o Test.so Test.hs module_init.c [1 of 1] Compiling Main ( Test.hs, Test.o ) Test.hs:1:0: The function `main' is not defined in module `Main' Second, I learned [2] that I have to pass in different flags on OS X, but unfortunately, GHC still wants me to have main. I'm probably doing something wrong here, is there anyone who can give me some pointers? (no pun intended). I'm running GHC 6.10.2 on Leopard. Thanks, -chris [1]: http://blog.haskell.cz/pivnik/building-a-shared-library-in-haskell/ [2]: http://www.mail-archive.com/haskell-cafe@haskell.org/msg51303.html___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] dsl and gui toolkit
That sounds really interesting, it would be great if you could share some of your work by putting it on hackage or posting a link to the repository! -chris On 5 okt 2009, at 12:42, Andrew U. Frank wrote: writing a gui is a mess (independent of wx or gtk) - too much detail is shown and not enough abstraction is done. haskell can help. i have written an experimental way of producing the GUI automatically with a description of the semantics of the types and operations involved (a la ontology, evnetually comparable what protege produces). the input is a descriptionof the entity ypes, the fields used, the functional dependencies between the fiels, plus the operations used. the division in screens and their layout. the rest ist automatic. the result is a GUI (with preferably gtk but i had also a wx version running). the ideas were inspired by eliot conal's work and wxgeneric, which seemed for administrative applications either too restricted or to specific. if somebody wants to try it out for his application, please write fr...@geoinfo.tuwien.ac.at (there is not much documentation and the code is not yet completely clean - testing by somebody else would be very valuable!) andrew ___ 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: Multiple-selection formlet?
Hey Colin, Currently, I don't think this is supported. It would help a lot if you could send me a dumbed-down version of your code, I'll file an issue for it on github. Thanks, -chris On 23 sep 2009, at 14:35, Colin Adams wrote: Just in case you missed it on the cafe. -- Forwarded message -- From: Colin Adams colinpaulad...@googlemail.com Date: 2009/9/21 Subject: Multiple-selection formlet? To: Haskell Cafe haskell-cafe@haskell.org I can't work out how to get multiple selections delivered from a formlet. I can add the multiple attribute to get the formlet to allow the user to make multiple selections, but I only get a single answer back. This seems inevitable from the type of rawSelect (or select) - since the list of values to select from is of type [(a, h)] and the result type is a. Am I missing something? -- Colin Adams Preston, Lancashire, ENGLAND -- Colin Adams Preston, Lancashire, ENGLAND ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with Text.XHtml.Strict.Formlets.file on Mac OSX
Hey Colin, The code looks OK to me. Are you sure you are setting the right method for your form? It's the third component of the tuple returned by the runFormState. Thanks, -chris On 22 sep 2009, at 08:56, Colin Adams wrote: I'm writing a form that involves picking a file to upload, and so uses Text.XHtml.Strict.Formlets.file. The form displays OK, but when I click the Browse button, and select a file from the dialog (no matter what the file type), and then click on the Submit button, I get an error: fval[2] is not a file I haven't added any validation yet. The generated html looks ok to me: input type=file name=fval[2] id=fval[2] This is on my laptop running Mac OSX. I can't test it on Linux until I get home at the weekend, so I don't know if I've made a silly error in my coding, but it is very simple: imageInputForm = F.plug (\xhtml - X.p (X.label Image file:) +++ xhtml) F.file Are there any known problems with the file formlet? Might it be OSX specific? -- Colin Adams Preston, Lancashire, ENGLAND ___ 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] Problem with Text.XHtml.Strict.Formlets.file on Mac OSX
OK, the trick is to set the attribute enctype=multipart/form-data on the form whenever your form contains a file upload item. Using the third parameter you can detect if this is the case. This is typical of using file-upload fields in web programming and independent of the formlets. It's also covered in the Happstack tutorial [1] and in the HTML form spec [2]. Good luck, -chris [1] http://tutorial.happstack.com/tutorial/file-uploads [2] http://www.w3.org/TR/html401/interact/forms.html#h-17.13.4 On 23 sep 2009, at 15:35, Colin Adams wrote: I'm not sure, but the other components of the form work (before I added the file bit, that is), so they will all be using the same method. I'm using a generic form-handling function named withForm that I got from one of the examples - this code appears to ignore the third component of the tuple. Note that I don't really understand all of this yet. 2009/9/23 Chris Eidhof ch...@eidhof.nl: Hey Colin, The code looks OK to me. Are you sure you are setting the right method for your form? It's the third component of the tuple returned by the runFormState. Thanks, -chris On 22 sep 2009, at 08:56, Colin Adams wrote: I'm writing a form that involves picking a file to upload, and so uses Text.XHtml.Strict.Formlets.file. The form displays OK, but when I click the Browse button, and select a file from the dialog (no matter what the file type), and then click on the Submit button, I get an error: fval[2] is not a file I haven't added any validation yet. The generated html looks ok to me: input type=file name=fval[2] id=fval[2] This is on my laptop running Mac OSX. I can't test it on Linux until I get home at the weekend, so I don't know if I've made a silly error in my coding, but it is very simple: imageInputForm = F.plug (\xhtml - X.p (X.label Image file:) +++ xhtml) F.file Are there any known problems with the file formlet? Might it be OSX specific? -- Colin Adams Preston, Lancashire, ENGLAND ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe -- Colin Adams Preston, Lancashire, ENGLAND ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Problem with monadic formlets
Hey everybody, I've just uploaded formlets 0.6.1 to Hackage, which should fix this bug. Thanks for letting me know! -chris On 29 aug 2009, at 13:22, Jeremy Shaw wrote: Hello, Yeah, it seems that checkM in formlets 0.6 broken. I reported the bug to MightByte as well. - jeremy At Fri, 28 Aug 2009 12:49:08 +0100, Colin Paul Adams wrote: Colin == Colin Paul Adams co...@colina.demon.co.uk writes: Jeremy == Jeremy Shaw jer...@n-heptane.com writes: Colin apparent data corruprion is occurring. I am suspecting a Colin bug in the formlets library (I have version 0.6). Colin So I have created a slightly cut-down (no database Colin involved) complete working program. Can you see if this Colin works ok with your version of formlets: I managed to uninstall formlets-0.6 myself, and then installed 0.5 instead. After adding the necessary extra argument to runFormletState (an empty string), the test program works fine. So this seems to be a bug in formlets-0.6. -- Colin Adams Preston Lancashire ___ 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] [ann] formlets 0.6
Hey everyone, I wanted to let you know that the formlets team has released a new version of the formlets [1] on hackage, a library to build type-safe, composable web forms. Most notably, Mightybyte and I worked on the massInput functionality, which is now ready for use! Mightybyte has an excellent article [2] on how to use the massInput to build dynamic forms on the client side. If you're building web apps with Haskell, make sure you check it out. -chris [1]: http://hackage.haskell.org/package/formlets [2]: http://softwaresimply.blogspot.com/2009/08/dynamic-list-formlets-in-haskell.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Are GADTs what I need?
Hey Kev, The types are thrown away during compile time. Therefore, if you have a constructor VWrapper :: a - Value nothing is known about that a when you scrutinize it. What you could do, however, is something like this: data Value a where VInt :: Integer - Value Integer ... VWrapper :: a - Value a And then you can write a function doSomething: doSomething :: Value String - String doSomething (VWrapper s) = s HTH, -chris On 13 jul 2009, at 12:41, Kev Mahoney wrote: Hi there, I'm currently writing an interpreter that I would like to be able to use with other haskell programs. I would like to be able to pass along arbitrary types though the interpreter. I've seen hints that GADTs can do this, but I am having trouble understanding them. So far, I've learnt you can do this: data Value where VInt :: Integer - Value ... VWrapper :: a - Value which can let you encode arbitrary 'dynamic' types into Value. I was hoping to be able to pattern match to get the value out again e.g. doSomething :: Value - doSomething (VWrapper String s) = . Also, anything that can help me out with GADTs in general will be much appreciated. Thanks, Kevin. ___ 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] Are GADTs what I need?
Then you could add a specific constructor for String. The main point is: the case construct only works for values, not for types. There is no typecase construct. If you want to have certain restrictions on the 'a', such as the Show class, you could also do something like this: data Value where VWrapper :: (Show a) = a - Value If you could elaborate a bit on what you're trying to accomplish (from a higher viewpoint) then maybe we can help you some more. -chris On 13 jul 2009, at 17:42, Kev Mahoney wrote: Thanks, that helps. I was hoping to not have to parametrize Value as there is a fair bit of code to change, and it cascades down through the data structures (maybe a forall a . Value a will help here?) I will have a go at this approach. In case anyone is interested the code is at http://github.com/KMahoney 2009/7/13 Chris Eidhof ch...@eidhof.nl: Hey Kev, The types are thrown away during compile time. Therefore, if you have a constructor VWrapper :: a - Value nothing is known about that a when you scrutinize it. What you could do, however, is something like this: data Value a where VInt :: Integer - Value Integer ... VWrapper :: a - Value a And then you can write a function doSomething: doSomething :: Value String - String doSomething (VWrapper s) = s HTH, -chris On 13 jul 2009, at 12:41, Kev Mahoney wrote: Hi there, I'm currently writing an interpreter that I would like to be able to use with other haskell programs. I would like to be able to pass along arbitrary types though the interpreter. I've seen hints that GADTs can do this, but I am having trouble understanding them. So far, I've learnt you can do this: data Value where VInt :: Integer - Value ... VWrapper :: a - Value which can let you encode arbitrary 'dynamic' types into Value. I was hoping to be able to pattern match to get the value out again e.g. doSomething :: Value - doSomething (VWrapper String s) = . Also, anything that can help me out with GADTs in general will be much appreciated. Thanks, Kevin. ___ 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] DHUG: meeting tomorrow (July 7th) in Utrecht
Hi everyone, The Dutch HUG [1] will meet again tomorrow. This time we'll meet in Utrecht again, at the Stairway To Heaven. The meeting will start at 19h. The venue is a sometimes a bit noisy, but there's beer and nice big tables. If you want to hear everything about the Dutch HUG straight from the horse's mouth: make sure you're at the meetings and subscribed to the mailing list [2]. We already have more than 40 members after two meetings! See you tomorrow! -chris [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] How to pretty print code efficiently
On 4 jul 2009, at 05:13, Alexander Dunlap wrote:
On Fri, Jul 3, 2009 at 6:45 PM, John Kynewho...@gmail.com wrote:
Hi,
Currently I'm pretty printing code by building arrays of strings
and calling
indent. For example:
instance JavaPrintableNamed AST.EnumeratedType where
javaLinesNamed parentName (AST.EnumeratedType memberDefinitions) =
[ public enum ++ asJavaId(parentName)
, {
] ++ memberCodeLines ++
[ }
,
]
where
memberCodeLines = indent $ javaLines memberDefinitions
The indent function takes a list of strings and adds an indent to the
beginning of every line.
I can imagine this to be very inefficient as it builds many strings
and
concatenates them.
In Ruby, I might do the same thing like this:
class EnumeratedType JavaPrintableNamed
def writeTo(writer)
writer.print public enum
writer.puts self.asJavaId
writer.puts {
writer.indent do
self.memberDefinitions.writeTo(writer)
writer.puts
end
where above, the writer.indent takes care of the indent, and
everything is
appended to a stream, which doesn't seem so bad in terms of
efficiency.
I'm looking for a way to do something similar in Haskell.
Anyone can give me a hand?
Thanks
-John
___
You may want to investigate the standard module
Text.PrettyPrint.HughesPJ, which contains a number of (I assume fairly
efficient) combinators for pretty printing.
I second that. Also, there is uulib which has a pretty printing module
that's quite similar:
http://hackage.haskell.org/packages/archive/uulib/0.9.10/doc/html/UU-PPrint.html
I think both packages are based on the paper The Design of a Pretty-
printing Library which can be found at http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps
Not only do they provide abstractions for things like indentation,
concatenation in different forms, etc., but they also are more
efficient than a naive implementation using lists.
-chris
-chris
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Re: [Haskell-cafe] ORM for haskell?
On 3 jul 2009, at 11:28, Jochem Berndsen wrote:
Chris Eidhof wrote:
I've something working that sort of does this. You define your
model in
the following way:
data User = User {name :: String, password :: String, age :: Int,
post
:: BelongsTo Post}
data Post = Post {title :: String, body :: String}
Then there's some boilerplate code (that ultimately will be
generated by
TH), and from that moment on you can do things like this:
test = do
conn - connectSqlite3 example.sqlite3
runDB conn $ do
user - fromJust $ find typeUser 1
user' - fillBelongsTo user relPost
return (post user')
By default, no relations will be fetched, but by doing the
fillBelongsTo
the user will be updated. I currently have support for new, update
and
find. All of this code is very alpha, and only works using HDBC and
Sqlite3, but still.
So in this example, both user and user' are of type User, but if I ask
for post user, this is undefined?
I have done something similar as you, except that I filled the related
field with an unsafePerformIO fetching the related data from the
database.
No, it will never be undefined. The BelongsTo datatype is defined as
following:
data BelongsTo a = BTNotFetched | BTId Int | BTFetched (Int, a)
So either there is no information available (BTNotFetched), we know
the id (the foreign key, BTId) or we know the id and the value
(BTFetched). It is currently just a proof of concept, but for me, an
extend version of this will do. I think that almost every mapping from
Haskell datatypes to a RDBMS will be slightly awkward, this is my way
to find a balance ;)
-chris
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Re: [Haskell-cafe] ORM for haskell?
Hey Marc,
On 30 jun 2009, at 19:52, Marc Weber wrote:
Is there anyone interested in helping building a library which
a) let's you define kind of model of you data
b) let's you store you model in any backend (maybe a relational
database)
c) does static checking of your queries at compilation time?
[...]
Maybe this does already exist and I've missed it?
I've something working that sort of does this. You define your model
in the following way:
data User = User {name :: String, password :: String, age :: Int,
post :: BelongsTo Post}
data Post = Post {title :: String, body :: String}
Then there's some boilerplate code (that ultimately will be generated
by TH), and from that moment on you can do things like this:
test = do
conn - connectSqlite3 example.sqlite3
runDB conn $ do
user - fromJust $ find typeUser 1
user' - fillBelongsTo user relPost
return (post user')
By default, no relations will be fetched, but by doing the
fillBelongsTo the user will be updated. I currently have support for
new, update and find. All of this code is very alpha, and only works
using HDBC and Sqlite3, but still.
You can find and fork my code on http://github.com/chriseidhof/
generics. I'll be happy to answer any questions about the code or the
ideas behind it.
-chris
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Re: [Haskell-cafe] Logo
Hey all, On 15 jun 2009, at 08:39, Ashley Yakeley wrote: Thomas Davie wrote: We had a lot of fun deciding Haskell's new logo, and while I don't agree with the final result, it would be nice if we could now start consistently using it. With that in mind, I realised that the Haskell Platform's logo is totally different, and did a quick mock up of a version reflecting the current Haskell logo. It needs someone with the original vector graphics to have a play and improve it a little bit, but hopefully you'll se a concept you like. I rather like the fact that the Haskell Platform logo is distinct from the Haskell logo. I think it helps prevent confusion (even though the Platform logo is based on one of the Haskell logo competition entrants). For new users, when they install Haskell they will install the Haskell Platform. I don't think we need to have a big distinction between that. Therefore, I think that the Haskell Platform should share the Haskell logo. I think the Haskell platform is an excellent name for internal communication, but to the outside world, it *is* Haskell. This is what you get when you install Haskell. Otherwise it will probably only confuse users. I think a typical new user would do something along the following lines: I want to play around with Haskell. I'll google for install Haskell or download Haskell (here, the Haskell Platform download page should be the #1 hit). There, the user sees the Haskell logo and doesn't have to know *anything* about the platform effort, cabal, ghc or whatever. Therefore, I think it should have the Haskell logo, not the platform logo. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Dutch HUG meeting tonight in Amsterdam
Hi everyone, Tonight there will be another meeting of the Dutch Haskell Users' Group! This time we'll meet in Amsterdam, in the library. On the wiki [1] you can find the details of how to reach it. We'll be at the top floor and shouldn't be hard to recognize. The meeting is set to begin at 19:30. Everybody's welcome, from beginners to advanced haskellers. Even if you never programmed in Haskell before it'll probably be a lot of fun. See you tonight! There are a lot of international people joining, so no knowledge of Dutch is necessary. If you're joining, also be sure to subscribe to our mailinglist [2]. See you tonight! -chris [1]: http://www.haskell.org/haskellwiki/Dutch_HUG [2]: http://groups.google.com/group/dutch-hug ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: ANNOUNCE: gitit 0.2 release - wiki using HAppS, git, pandoc
If anyone else has problems installing gitit, try updating your cabal- install (and cabal). I had old versions on my computer, and updating them solved my gitit build-problems. -chris On 9 nov 2008, at 22:41, John MacFarlane wrote: I've just uploaded a new version (0.2.1) that requires HAppS = 0.9.3 0.9.4. (There are small API changes from 0.9.2 to 0.9.3, so I thought it best not to allow 0.9.2.x, even though it still compiles with a warning.) +++ Hugo Pacheco [Nov 09 08 20:41 ]: a new HAppS version [1]0.9.3.1 has been released, and gitit requires HApps==[2]0.9.2.1. should ti be ok just to relax the dependency? On Sat, Nov 8, 2008 at 8:32 PM, John MacFarlane [EMAIL PROTECTED] wrote: I've uploaded an early version of gitit, a Haskell wiki program, to HackageDB. Gitit uses HAppS as a webserver, git for file storage, pandoc for rendering the (markdown) pages, and highlighting- kate for highlighted source code. Some nice features of gitit: - Pages and uploaded files are stored in a git repository and may be added, deleted, and modified directly using git. - Pages may be organized into subdirectories. - Pandoc's extended version of markdown is used, so you can do tables, footnotes, syntax-highlighted code blocks, and LaTeX math. (And you can you pandoc to convert pages into many other formats.) - Math is rendered using jsMath (which must be installed separately). - Source code files in the repository are automatically rendered with syntax highlighting (plain/text version is also available). You can check it out on my webserver: [4]http://johnmacfarlane.net:5001/ Or try it locally: cabal update cabal install pandoc -fhighlighting cabal install gitit gitit # note: this will create two subdirectories in the working directory # then browse to [5]http://localhost:5001. There's a git repository at [6]http://github.com/jgm/gitit/tree/master . Comments and patches are welcome. John ___ Haskell-Cafe mailing list [EMAIL PROTECTED] [8]http://www.haskell.org/mailman/listinfo/haskell-cafe -- [9]www.di.uminho.pt/~hpacheco References Visible links 1. http://0.9.3.1/ 2. http://0.9.2.1/ 3. mailto:[EMAIL PROTECTED] 4. http://johnmacfarlane.net:5001/ 5. http://localhost:5001/ 6. http://github.com/jgm/gitit/tree/master 7. mailto:Haskell-Cafe@haskell.org 8. http://www.haskell.org/mailman/listinfo/haskell-cafe 9. http://www.di.uminho.pt/~hpacheco ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: [Haskell] Probably a trivial thing for people knowing Haskell
I think it might be more appropriate to move this discussion to haskell-cafe. On 19 okt 2008, at 17:24, Friedrich wrote: Learn to love types: one of the neat things about Haskell is that if you can write down the type of a function then you have usually done 90% of the work of writing the code for it. Well I disagree. But that's another story. Well, it's definitely not true when you're starting out with Haskell. The thing is: once you start to think in types it does work like this. You just think: what do I need as my input and what's my output. That's what you write down as your type and you're almost done! It's very similar to test-driven development; the point with TDD is not so much about making sure your program is correct: the big win (for me) is that it helps you think about the design of your program. The same holds for types. Another is that in general, if you can't express the type of a function, it means you haven't thought through what you're trying to do. No that's not true. The use implies that. However I'm not advice resistant and will see if I use types. But IMHO that's should be job of the environment to figure out correctly and most of the time Haskell does guess right. And I surely can ask for the types. I agree. However, sometimes, when things get really complex, you can't figure out a way to write down the code. That's when it can be handy to start out from the types and slowly work towards the definition. At first, you'll think that types are there to make your life harder. After a while, you'll start to love them and to be honest: I feel quite uncomfortable programming in an untyped language these days ;). -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Updated formlets sample?
Ah yes, I just adjusted the code until it compiled, I must confess I didn't check whether it actually worked ;). Thanks for the wiki-update! -chris On 22 sep 2008, at 09:47, Martin Huschenbett wrote: Hi Chris, you're absolutely right. The mistake was in the where-part of withForm. The function handleOk' gets an environment d as argument but uses an extractor that was created without passing d to runFormState. I've put a corrected version on hpaste [1] and also posted it to the wiki on haskell.org [2]. Hope this is ok for you? Regards, Martin. [1] http://hpaste.org/10568#a1 [2] http://haskell.org/haskellwiki/Formlets Chris Eidhof schrieb: That means that you don't have input0 in your environment, maybe you're passing in an empty environment? -chris On 21 sep 2008, at 12:11, Martin Huschenbett wrote: Hi Chris, thanks for the updated example. Compiling works now. But when I try to run it I alway get error messages like [input0 is not in the data,input1 is not in the data] Regards, Martin. Chris Eidhof schrieb: Hey Martin, On 19 sep 2008, at 04:14, Martin Huschenbett wrote: I found a blog post concerning formlets [1] in the web. Since looks very interesting I tried to compile the sample code with recent versions of HAppS and formlets from hackage. But this didn't work as the API of formlets has changed since this post. I tried to adopt the code to the new API but I was unable to finish this since there is a new monadic context I don't know to handle in the right way. So my question is, is there an updated version of this sample code in the web or has anybody tried to adopt it and can send me the results? Yes, I'm sorry for that. The API is still very immature and due to changes, that's also why it hasn't been officially announced yet. I've just put an updated example at http://hpaste.org/10568, hope that'll work for you. I guess we should build a small homepage / wikipage that always has an up-to-date example. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Updated formlets sample?
Hey Martin, On 19 sep 2008, at 04:14, Martin Huschenbett wrote: I found a blog post concerning formlets [1] in the web. Since looks very interesting I tried to compile the sample code with recent versions of HAppS and formlets from hackage. But this didn't work as the API of formlets has changed since this post. I tried to adopt the code to the new API but I was unable to finish this since there is a new monadic context I don't know to handle in the right way. So my question is, is there an updated version of this sample code in the web or has anybody tried to adopt it and can send me the results? Yes, I'm sorry for that. The API is still very immature and due to changes, that's also why it hasn't been officially announced yet. I've just put an updated example at http://hpaste.org/10568, hope that'll work for you. I guess we should build a small homepage / wikipage that always has an up-to-date example. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Type family fun
Hey all, I was playing around with type families, and I have a strange problem. Suppose we have an alternative to an Either datatype: data (:|:) a b = Inl a | Inr b and a class Ix: class Ix i where type IxMap i :: * - * empty :: IxMap i [Int] Now I want to give an instance for (a :|: b): instance (Ix l, Ix r) = Ix (l :|: r) where type IxMap (l :|: r) = BiApp (IxMap l) (IxMap r) empty = BiApp empty empty BiApp is defined as following: data BiApp a b c = BiApp (a c) (b c) However, it looks like the recursive calls to empty can't be unified, I get the following error message: Couldn't match expected type `IxMap l' against inferred type `IxMap i' Expected type: IxMap (l :|: r) [Int] Inferred type: BiApp (IxMap i) (IxMap i1) [Int] In the expression: BiApp empty empty In the definition of `empty': empty = BiApp empty empty In the inferred type, there should be IxMap l instead of IxMap i, does anybody know what I'm doing wrong? Thanks, -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: [Haskell] Compiler Construction course using Haskell?
I plan to give a course in compiler construction, using Haskell as the implementation language (not as source or target language). Something along these lines: 1. combinator parsers (Parsec), 2. simple interpreter (arithmetical expressions) 3. add algebraic data types, functions 4. type checker 5. code generator. Ideally, 2..5 would be using the very same tree traversal code and just change the monad for evaluation. Any comments appreciated. Have you given such a course? Taken? At Utrecht University, they teach excellent courses on exactly this subject, using Haskell. The course webpage [1] is probably a useful resource for you, as it shows exactly what we were thought (I participated in the course last year). We made heavy use of Utrecht's Attribute Grammar Compiler [2], which is a pre-processor for Haskell that allows you to very easily build programs using an attribute grammar. This proved to be a really nice way to do the tree transformations. I very much liked the idea of attribute grammars, but I personally don't like pre-processors very much. Also, we targeted Simple Stack Machine as a platform. This is an assembly-like language that has a graphical interpreter, so you can actually see your code, do single-stepping, see your stack, etc. It proved to be quite useful. As a student, I it added a lot of educational value, but a real language would also be cool (e.g. Harpy [4]). HTH, -chris [1]: http://www.cs.uu.nl/docs/vakken/ipt/ [2]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/uuagc [3]: http://people.cs.uu.nl/atze/SSM/index.html [4]: http://uebb.cs.tu-berlin.de/harpy/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Sphinx full-text searching client on Hackage
Hey everyone, We started working on a client [1] for the sphinx full-text search engine [2], which is a very fast full-text search engine that has either SQL or XML as a backend. While our version is far from done (it only supports the query command, and a limited number of parameters), we still think that it might be useful for other people as well. If you want to help us hacking on it, testing it or improving documentation, you're more than welcome. The communication with Sphinx is done using a quite low-level binary protocol, but Data.Binary saved the day: it made it very easy for us to parse all the binary things. Especially the use of the Get and Put monads are a big improvement over the manual reading and keeping track of positions, as is done in the PHP/Python clients. Thanks, -chris [1]: http://hackage.haskell.org/cgi-bin/hackage-scripts/package/sphinx [2]: http://www.sphinxsearch.com/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Compiling GHC 6.8.3 on OS X with readline support
Hey all, When compiling GHC 6.8.3 on OS X, I ended up with a GHCi without readline support. That makes interacting quite hard, especially because the Backspace-key didn't even work. With some help on irc from Baughn and by reading a blog post from Paul Brown, I managed to get readline working after all. After installing readline from fink, I had to pass the following options to configure: ./configure --with-readline-includes=/sw/include/readline --with- readline-libraries=/sw/lib After that make and sudo make install worked just fine, and I had readline again! I wrote this down in case anybody else has had the same problems. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] The state of database libraries
Hey everyone, I'm figuring out how to do databases in Haskell (on OS X). So far, I've tried the following approaches: 1. hdbc. I'd like to connect to MySQL, so I need the ODBC backend. I couldn't get this to work under OS X, while I installed myodbc, which seems to be broken. 2. hsql. The packages on hackage don't compile, so I grabbed the darcs version. hqsl itself installed perfectly, but when I try to compile hsql-mysql, it does not recognize that hsql is already installed and tries to recompile. Compiling fails, so I generated a .tar.gz of hsql using cabal sdist, put it in the .cabal/packages directory in the right place, and finally, it does compile. Now hsql-mysql starts compiling, but it finally fails with: MySQL.hsc:270:0: error: ‘MYSQL_NO_DATA’ undeclared (first use in this function) MySQL.hsc:270:0: error: (Each undeclared identifier is reported only once MySQL.hsc:270:0: error: for each function it appears in.) So what is the state of hsql? And haskelldb? Are they actively maintained? Thanks, -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] IMAP and NNTP libraries
On 23 jun 2008, at 22:26, Spencer Janssen wrote: On Sun, Jun 22, 2008 at 02:52:33AM -0300, Maurí cio wrote: Hi, Are there mature libraries for IMAP and NNTP available to Haskell? Thanks, Maurício There is the haskellnet project: http://darcs.haskell.org/SoC/haskellnet/ I'm not sure whether it is mature or maintained. I don't think it's maintained or mature: last time I checked, I couldn't get it to work (probably due to library changes), and there is not a lot of documentation nor comments. I was actually thinking of writing a binding myself, to libEtPan!, which seems to have a well-documented and clean interface. I'm not sure how hard this is though. I've also looked a bit at the UW c- client, but I haven't seen any good examples of how to use it. -chris___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] wanted: Network.Curl examples
Hey Brad, I wrote a blog-post with some curl-examples in there, it's a small mashup of last.fm and upcoming, check it at http://tinyurl.com/5d8jx7 Enjoy, -chris On 11 jun 2008, at 07:51, brad clawsie wrote: -BEGIN PGP SIGNED MESSAGE- Hash: SHA1 in search of some trivial examples using Network.Curl, preferrably posted here: http://haskell.org/haskellwiki/Network.Curl some of this stuff i can figure out, but setting the curl WriteFunction, as discussed here: http://code.haskell.org/~dons/docs/curl/Network-Curl-Opts.html#t%3AWriteFunction is nonobvious. any info would be useful, curl is a great library and it would be nice if using it were more straightforward thanks brad -BEGIN PGP SIGNATURE- Version: GnuPG v2.0.9 (FreeBSD) iEYEARECAAYFAkhPaAAACgkQxRg3RkRK91OQrQCfTt+xzvqIAxDkqq8/P85ZZjON HWgAoK3L/1JUQjdaWHcHfutKvI3nPJUc =BfuR -END PGP SIGNATURE- ___ 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] Simple list processing
Hey Andrew, On 11 jun 2008, at 20:17, Andrew Coppin wrote: According to the theory, anything that consumes a list and produces a value is some kind of fold. [Assuming it traverses the list in a sensible order!] So it looks like you could implement this as a fold. But should that be a LEFT-fold or a RIGHT-fold? (I always get confused between the two!) Check out http://foldl.com/ and http://foldr.com ;) -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] [ANN] Twitter Client
Hey everyone, I was tired of all those graphical Twitter clients that aren't usable from my Terminal, so I wrote my own. It's still very much alpha, but comments or improvements are more than welcome. You can install it by downloading the twitter-package from hackage. In order to get it to work, create a file ~/.twitter with the contents username:password, and you should be set. The source code isn't polished yet, but it makes heavy use of the new curl, json and xml libraries from Galois, so it might be interesting to browse the source. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] parser
On 7 dec 2007, at 22:55, Ryan Bloor wrote:
hi
The thing is... it will be a simple parser really. The expressions
are already defined and we can't use parsec imports. Below is the
types I have.
I have a function that removes initial spaces from the start of a
string. A function that checks if a substring is part of another
string, which use the remove space function also.
The next function is: which uses the type:
type Parser = String - [(Expr,String)]
So what does this type really mean? You give it a string, and it will
return a list of (Expr, String). I would guess that the list is all
possible outcomes, and the String in (Expr, String) is probably the
rest of the parsed data. If you want to find a correct parse, you
probably want to select the first element from that list that has an
empty rest.
You could write a parser that parses single digits:
parseDigit :: String - [(Int, String)]
parseDigit (x:xs) | isDigit x = [read x]
Of course you have to define the other cases for parseDigit. If you
had a parseMany function that parses many things of the same type, you
could combine that with parseDigit to parse natural numbers. The other
thing you are really going to need is a choice-operator. In your
example, you want to parse terms that are either numbers or term +
term:
parseTerm = parseNaturalNumber `parseOr` parseAddition
It's probably best to read a good book or tutorial on parsers. There
is an excellent textbook on grammars and parsing in Haskell [1], it
probably explains exactly what you want.
-chris
[1] Johan Jeuring, Doaitse Swierstra: Grammars and Parsing:
http://www.cs.uu.nl/docs/vakken/gont/diktaat.pdf
readExpression :: String - Expr
e.g. readExpression True = EBool True
e.g. readExpression (23 + 67) = EAdd (EInt 23) (EInt 67)
Types--
data Type = TNone -- badly typed values
| TInt -- integer values
| TBool -- boolean values
deriving Show
data Expr = EInt {vInt :: Int} -- integer values
| EBool {vBool :: Bool} -- boolean values
| EAdd Expr Expr -- (e1 + e2)
| EMin Expr Expr -- (e1 - e2)
| EMul Expr Expr -- (e1 * e2)
| EAnd Expr Expr -- (e1 e2)
| EOr Expr Expr -- (e1 || e2)
| ENot Expr -- not e1
| EComp Expr Expr -- (e1 == e2)
| ETest Expr Expr Expr -- if e1 then e2 else e3
| ENone -- badly formed expressions
CC: haskell-cafe@haskell.org
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Haskell-cafe] parser
Date: Fri, 7 Dec 2007 22:17:54 +0100
On 6 dec 2007, at 18:06, Ryan Bloor wrote:
Can anyone advise me on how to check whether a string contains
ints,
chars, bools, etc
2345 + 6767 shoudl give IntAdd (2345) (6767)
2345 should give IntT 2345
You need to write a parser. There are a lot of libraries that will
help you write a parser. One library that is often used for writing
parsers in Haskell is called Parsec [1]. There's good
documentation on
that site on how to use it. Parsec is already included in you
distribution. Good luck!
-chris
[1]: http://legacy.cs.uu.nl/daan/parsec.html
Get closer to the jungle… I'm a Celebrity Get Me Out Of Here!
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Re: [Haskell-cafe] parser
On 7 dec 2007, at 23:51, Ryan Bloor wrote:
i am using hugs and the isDigit and anything 'is' doesn't work...
they must have forgot to add them in! Does GHC work with them.
Yes, it's in base. Alternatively, you could write the functions
yourself, they're not that hard.
p.s... that book looks fantastic... bette than the ones i got from
the library; too specific.
also... when and where do i use my predetermined types(EBool) and
how...?
I think that is explained in the book. It's also not too hard to
figure out yourself. A good strategy for writing Haskell programs in
general is to think of the types first: what types should your
functions have? Often this will help you in thinking of a good
implementation.
The first thing you want to do, is parametrize the return-type of your
parser. Instead of having type Parser = [(ETerm, String)] you probably
want: type Parser a = String - [(a, String)]. With that type, you
could do something like:
parseDigit :: Parser Int
parseMany :: Parser a - Parser [a]
parseOr :: Parser a - Parser a - Parser a
You can use these types to come up with the functions.
-chris
Ryan
CC: haskell-cafe@haskell.org
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Haskell-cafe] parser
Date: Fri, 7 Dec 2007 23:31:38 +0100
On 7 dec 2007, at 22:55, Ryan Bloor wrote:
hi
The thing is... it will be a simple parser really. The expressions
are already defined and we can't use parsec imports. Below is the
types I have.
I have a function that removes initial spaces from the start of a
string. A function that checks if a substring is part of another
string, which use the remove space function also.
The next function is: which uses the type:
type Parser = String - [(Expr,String)]
So what does this type really mean? You give it a string, and it
will
return a list of (Expr, String). I would guess that the list is all
possible outcomes, and the String in (Expr, String) is probably the
rest of the parsed data. If you want to find a correct parse, you
probably want to select the first element from that list that has an
empty rest.
You could write a parser that parses single digits:
parseDigit :: String - [(Int, String)]
parseDigit (x:xs) | isDigit x = [read x]
Of course you have to define the other cases for parseDigit. If you
had a parseMany function that parses many things of the same type,
you
could combine that with parseDigit to parse natural numbers. The
other
thing you are really going to need is a choice-operator. In your
example, you want to parse terms that are either numbers or term +
term:
parseTerm = parseNaturalNumber `parseOr` parseAddition
It's probably best to read a good book or tutorial on parsers. There
is an excellent textbook on grammars and parsing in Haskell [1], it
probably explains exactly what you want.
-chris
[1] Johan Jeuring, Doaitse Swierstra: Grammars and Parsing:
http://www.cs.uu.nl/docs/vakken/gont/diktaat.pdf
readExpression :: String - Expr
e.g. readExpression True = EBool True
e.g. readExpression (23 + 67) = EAdd (EInt 23) (EInt 67)
Types--
data Type = TNone -- badly typed values
| TInt -- integer values
| TBool -- boolean values
deriving Show
data Expr = EInt {vInt :: Int} -- integer values
| EBool {vBool :: Bool} -- boolean values
| EAdd Expr Expr -- (e1 + e2)
| EMin Expr Expr -- (e1 - e2)
| EMul Expr Expr -- (e1 * e2)
| EAnd Expr Expr -- (e1 e2)
| EOr Expr Expr -- (e1 || e2)
| ENot Expr -- not e1
| EComp Expr Expr -- (e1 == e2)
| ETest Expr Expr Expr -- if e1 then e2 else e3
| ENone -- badly formed expressions
CC: haskell-cafe@haskell.org
From: [EMAIL PROTECTED]
To: [EMAIL PROTECTED]
Subject: Re: [Haskell-cafe] parser
Date: Fri, 7 Dec 2007 22:17:54 +0100
On 6 dec 2007, at 18:06, Ryan Bloor wrote:
Can anyone advise me on how to check whether a string contains
ints,
chars, bools, etc
2345 + 6767 shoudl give IntAdd (2345) (6767)
2345 should give IntT 2345
You need to write a parser. There are a lot of libraries that
will
help you write a parser. One library that is often used for
writing
parsers in Haskell is called Parsec [1]. There's good
documentation on
that site on how to use it. Parsec is already included in you
distribution. Good luck!
-chris
[1]: http://legacy.cs.uu.nl/daan/parsec.html
Get closer to the jungle… I'm a Celebrity Get Me Out Of Here!
Can you guess the film? Search Charades!
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Re: [Haskell-cafe] parser
On 6 dec 2007, at 18:06, Ryan Bloor wrote: Can anyone advise me on how to check whether a string contains ints, chars, bools, etc 2345 + 6767 shoudl give IntAdd (2345) (6767) 2345 should give IntT 2345 You need to write a parser. There are a lot of libraries that will help you write a parser. One library that is often used for writing parsers in Haskell is called Parsec [1]. There's good documentation on that site on how to use it. Parsec is already included in you distribution. Good luck! -chris [1]: http://legacy.cs.uu.nl/daan/parsec.html ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] return in Monad class necessary?
On 27 nov 2007, at 10:14, Reinier Lamers wrote: Chris Eidhof wrote: On 26 nov 2007, at 19:48, Henning Thielemann wrote: I wonder whether it is a typical mistake of beginners to write 'return' within a do-block (that is, not at the end) and if it is possible to avoid this mistake by clever typing. In a proper monad 'return' can be fused with subsequent actions, and thus it is not necessary within a sequence of actions. However, although sensible, 'return' is also not required at the end of a block. Has someone already thought about a replacement for monads? I also made that mistake in the beginning, I used return instead of lets. I don't think it's a big problem, most users will find out once they've got some more experience, and it doesn't really do any harm. It might be possible for the compiler to emit a warning when a return is used in the middle of a do block as the top level operator on a line. OTOH, that still wouldn't catch something like when (x == 0) (return ()) which doesn't do what an imperative programmer expects. Well, there are two things about the return: First, some people want to use return just as an imperative programmer would use it: to exit from a function. So the programmer doesn't expect the commands after that return are executed. Second, the problem I had was that I didn't know how to do computations with the data I got from the monad, for example: main = do myLine - getLine reversed - return $ unwords $ reverse $ words myLine putStrLn reversed Instead of the 3rd line I could have written let reversed = unwords $ reverse $ words myLine This is another problem, but it doesn't affect the computation, whereas the first problem is more serious. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] return in Monad class necessary?
On 26 nov 2007, at 19:48, Henning Thielemann wrote: I wonder whether it is a typical mistake of beginners to write 'return' within a do-block (that is, not at the end) and if it is possible to avoid this mistake by clever typing. In a proper monad 'return' can be fused with subsequent actions, and thus it is not necessary within a sequence of actions. However, although sensible, 'return' is also not required at the end of a block. Has someone already thought about a replacement for monads? I also made that mistake in the beginning, I used return instead of lets. I don't think it's a big problem, most users will find out once they've got some more experience, and it doesn't really do any harm. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] RLE in Haskell: why does the type variable get instantiated?
Hey Haskell-Cafe, I was trying out the code in Dons's article [1], and I noticed a weird thing when doing it in GHCi. When binding the function composition to a variable, the type suddenly changes. I'm not completely sure why this happens. Is this because GHCi is in a monad and wants to find an instance for the type variable? Here's my GHCi session: Prelude :m +Control.Arrow Prelude Control.Arrow :m + List Prelude Control.Arrow List :t map (length head) . group map (length head) . group :: (Eq a) = [a] - [(Int, a)] Prelude Control.Arrow List let encode = map (length head) . group Prelude Control.Arrow List :t encode encode :: [Integer] - [(Int, Integer)] Thanks, -chris [1]: http://cgi.cse.unsw.edu.au/~dons/blog/2007/07/31 ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Silly mail client
One thing I did was replacing the Reply button in my toolbar with Reply All. The only problem is that I always use Cmd+R instead of clicking a button, but I'm at least a little bit closer. -chris On 6-mei-2007, at 15:21, [EMAIL PROTECTED] wrote: Andrew Coppin [EMAIL PROTECTED] writes: OK, this is hacking me off now... Does ANYBODY know how I can convince Thunderbird to send replies to Haskell Cafe rather than sending them to the original poster? This is really becoming tiresome... My best approach to that has been to explicitely rewrite the Reply-To with procmail when the mail arrives at my place. The problem is, that the 'List-Id' tag will only work, if all clients stick to the implied rules (which they don't) and if you don't have a MTA or mailbox storage (like cyrus) which eliminates duplicates (then answers copied to you arrive earlier, leading to elimination of the copy with the List-Id tag). After long and careful study I've come to the conclusion that every magic based on headers inserted by the mailing list and based on all participants mail clients sticking to some rules won't work. Originally, as I understand it, the Mail-Followup-To field had been intended to indicate an address for reply to list. But most mail clients don't support it. I'm not sure wether Thunderbird supports it, but I've heard a reply all would reply to the address indicated in Mail-Followup-To. The problem is anyway (a) Haskell Cafe does not provide the field and (b) duplicate elimination would quite possibly kick the wrong mail copy (that which has Mail-Followup-To set). So my suggestion: 1) Use procmail 2) Detect haskell-cafe in the headers 3) Add the List-Id and Mail-Followup-To at you side. 4) If you have client which doesn't respect Mail-Followup-To (try reply all), then also add a Reply-To header. (4) means, if you wan't to reply by mail to the individual author, you'll have to edit the receiver address by hand. Regards -- Markus ___ 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] Why the Prelude must die
On Mar 24, 2007, at 2:36 AM, Sebastian Sylvan wrote: On 3/24/07, Chris Eidhof [EMAIL PROTECTED] wrote: Given all these issues, I consider the only reasonable option is to discard the Prelude entirely. There will be no magic modules. Everything will be an ordinary library. HOFs like (.) are available from Control.Function. List ops come from Data.List. Any general abstractions can be added in abstract Sequence, Monad, etc. modules. Haskell will regain the kind of organic evolution whose lack currently causes Haskell to lose its lead over Python et al by the day. I basically agree with a lot of the things you say. The only thing is: it's so convenient to have the Prelude. I can just start writing my haskell programs and don't have to worry about all kinds of imports. And you'll end up being repetitive: you'll import (.) and stuff like that in _every_ file. Yeah, this will definitely be more modular, but if we go for it, it's going to be so much more (tedious) work to create a new program. The solution is simple: * If there is a module M where clause in the beginning of the file, then it's a proper module and shouldn't import the Prelude. * If there is no module declaration then it's a quick'n dirty script and should have the Prelude implicitly imported. * Interactive interpreters should probably import the Prelude. So if I'm writing a script, which has been working, then import Control.Monad, it all suddenly stops working? I also think that you want to minimize the differences between an interpreted (interactive) version and a compiled version. It would be very weird for first-time users if their scripts work in ghci but break when they compile them. I'm sorry for being so negative. I like the idea, but I don't like it from a newbie-standpoint. The thing is: this is mostly handy for power-users, maybe we should do it for power-users only? We can still change the prelude to have no more code in there, but make it only a bunch of imports? -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Why the Prelude must die
Given all these issues, I consider the only reasonable option is to discard the Prelude entirely. There will be no magic modules. Everything will be an ordinary library. HOFs like (.) are available from Control.Function. List ops come from Data.List. Any general abstractions can be added in abstract Sequence, Monad, etc. modules. Haskell will regain the kind of organic evolution whose lack currently causes Haskell to lose its lead over Python et al by the day. I basically agree with a lot of the things you say. The only thing is: it's so convenient to have the Prelude. I can just start writing my haskell programs and don't have to worry about all kinds of imports. And you'll end up being repetitive: you'll import (.) and stuff like that in _every_ file. Yeah, this will definitely be more modular, but if we go for it, it's going to be so much more (tedious) work to create a new program. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] XML Validation and Digestion in Haskell
Don't spend too much time on the various libraries though. I tried some simple things with Haskell and XML, but I found it really hard to actually parse a simple document. You really don't want to write your own parser. The only tool that worked for me was HXT, which is based on arrows. These are pretty hard to grasp right away, but really powerful. I really like the way they are used in HXT, but it still feels a bit weird sometimes. Good luck, and keep us posted. -chris On Mar 22, 2007, at 7:52 AM, Andrew Wagner wrote: Hi Arun, Your problem description seems a little vague - which is understandable, considering how embedded in your business model it is. As for general recommendations, I'm no guru, but I would suggest looking at the existing XML libraries in Haskell [1], and if that's not powerful enough, check out parsec[2] for building a custom parser. I think to get more specific recommendations, you would need to give more details about the problem. Hope this helps somewhat. Andrew [1]: http://www.haskell.org/haskellwiki/Libraries_and_tools/ Web_programming#XML_2 [2]: http://www.cs.uu.nl/people/daan/download/parsec/parsec.html On 3/22/07, Arun Suresh [EMAIL PROTECTED] wrote: Hi.. I am currently working on a project where basically we do a lot of XML validation and digestion. For example : We recieve an XML document A, if the document passes schema validation, we do some business level validations, then from A, we create XML digests B, C and D. Our code-base is written completely in Java. We had earlier tried using XSLT, but it became too unwieldy to manage (we ended up making calls to other Java classes from the XSLT engine) The problem we are facing right now is that we have huge hierarchies of Validators, Digestors and Contexts. It just doesnt look right. I just cant help but wonder if theres a better way of doing this... I have been trying to get my hands dirty with Haskell for a couplo weeks now. all the while keeping the problem at hand in the back of my mind.. I just dont seem to be see how applying functional programming concepts can help in this scenario.. Was wondering if somebody could probably give me some pointers.. Regards Arun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] XML Validation and Digestion in Haskell
Hey Aron, I think you intended to CC Haskell Café as well. HaXml has support for DtdToHaskell, but HXT supports validating with a Relax NG validator. I guess the best way to figure it out is thoroughly read the documentation. -chris On Mar 22, 2007, at 10:40 PM, Arun Suresh wrote: thanks for the feedback you guyz.. First off.. I went through the HaXml documentation.. It looks pretty promising.. and as far as HXT is concerned.. I guess ill be spending the weekend grappling with the concept of Arrows and monads in general :) I dont know if HXT or HaXml offers it.. but I was wondering if either of them provides some sort of schema compilation facility.. (a la XmlBeans.. for those from the Java world).. basically I was wondering if given an XML schema, is there a utility that will generate a Haskell type hierarchy from the same ?? regards Arun On 3/23/07, Chris Eidhof [EMAIL PROTECTED] wrote:Don't spend too much time on the various libraries though. I tried some simple things with Haskell and XML, but I found it really hard to actually parse a simple document. You really don't want to write your own parser. The only tool that worked for me was HXT, which is based on arrows. These are pretty hard to grasp right away, but really powerful. I really like the way they are used in HXT, but it still feels a bit weird sometimes. Good luck, and keep us posted. -chris On Mar 22, 2007, at 7:52 AM, Andrew Wagner wrote: Hi Arun, Your problem description seems a little vague - which is understandable, considering how embedded in your business model it is. As for general recommendations, I'm no guru, but I would suggest looking at the existing XML libraries in Haskell [1], and if that's not powerful enough, check out parsec[2] for building a custom parser. I think to get more specific recommendations, you would need to give more details about the problem. Hope this helps somewhat. Andrew [1]: http://www.haskell.org/haskellwiki/Libraries_and_tools/ Web_programming#XML_2 [2]: http://www.cs.uu.nl/people/daan/download/parsec/parsec.html On 3/22/07, Arun Suresh [EMAIL PROTECTED] wrote: Hi.. I am currently working on a project where basically we do a lot of XML validation and digestion. For example : We recieve an XML document A, if the document passes schema validation, we do some business level validations, then from A, we create XML digests B, C and D. Our code-base is written completely in Java. We had earlier tried using XSLT, but it became too unwieldy to manage (we ended up making calls to other Java classes from the XSLT engine) The problem we are facing right now is that we have huge hierarchies of Validators, Digestors and Contexts. It just doesnt look right. I just cant help but wonder if theres a better way of doing this... I have been trying to get my hands dirty with Haskell for a couplo weeks now. all the while keeping the problem at hand in the back of my mind.. I just dont seem to be see how applying functional programming concepts can help in this scenario.. Was wondering if somebody could probably give me some pointers.. Regards Arun ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] A real Haskell Cookbook
Hey everyone, we added some examples to this page. There are some topics that don't have any examples, notably: # 11 Network Programming # 12 XML * 12.1 Parsing XML # 13 Databases * 13.1 MySQL * 13.2 PostgreSQL * 13.3 SQLite # 14 FFI * 14.1 How to interface with C If anyone feels like filling up some of those sections, that would be great. -chris On 21 Feb, 2007, at 20:17 , Martin Bishop wrote: I made a preliminary page, and fleshed out some of the headers/sub- headers on the wiki page for a good Haskell Cookbook (aka NOT a PLEAC clone). Please contribute and/or fix the examples and explanations so we can make a really nice Cookbook for newbies. :) http://haskell.org/haskellwiki/Cookbook ___ 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] Hi can u explain me how drop works in Haskell
Hey, you're almost there: drop :: Integer - [a] - [a] drop 0 xs = xs drop n (x:xs) = drop (n-1) xs Your version fails when trying to do drop 10 [1..10]. My version fails when trying to do drop 10 [1..9], so you might want to try to see if you can come up with a solution for that! Good luck, -chris On 25 Feb, 2007, at 18:43 , iliali16 wrote: Hi I am trying to implement the function drop in haskell the thing is that I I have been trying for some time and I came up with this code where I am trying to do recursion: drop :: Integer - [Integer] - [Integer] drop 0 (x:xs) = (x:xs) drop n (x:xs) |n lList (x:xs) = dropN (n-1) xs : |otherwise = [] So I want to understand how would this work and what exacttly should I put as an answer on line 4 couse that is where I am lost. I know I might got the base case wrong as well but I don't know what to think for it. I have done the lList as a function before writing this one. Thanks to those who can help me understand this. Thanks alot in advance! Have a nice day! -- View this message in context: http://www.nabble.com/Hi-can-u- explain-me-how-drop-works-in-Haskell-tf3290490.html#a9152251 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 mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Recursion in Haskell
The definition of myLen says: myLen [] = 0 The length for an empty list is zero myLen (x:xs) = 1 + myLen xs The length of a list containing x and some other stuff (xs) is 1 + (the length of the other stuff). So basically, if you've got a list [1,2,3], it will try to do this: myLen (1:[2,3]) = 1 + myLen [2,3] The length of [1,2,3] is 1 + the length of [2,3] myLen (2:[3]) = 1 + myLen [3] The length of [2,3] = 1 + the length of [3] myLen (3:[]) = 1 + myLen [] This is the tricky part, now the other case of myLen is being called: myLen [] = 0 Here you can see that it won't recurse anymore. Now there is going to be some replacement: myLen (3:[]) can now be calculated, because myLen [] is now known (0). Because we know this, myLen (2:[3]) can now be calculated too, because we know that myLen [3] is 1. And so on. I think the trick here is to see that [1] is exactly the same as 1: []. Once you grasp this, the rest will probably easy. Good luck! -chris On 17 Feb, 2007, at 19:32 , P. R. Stanley wrote: Hi I understand the basic principle of recursion but have difficulty with the following: -- a recursive function -- for calculating the length of lists myLen [] = 0 myLen (x:xs) = 1 + myLen xs What's happening here? Top marks for a comprehensive jargon-free explanation. Thanks in advance Paul ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Is Excel the most used -- and fucntional -- programming lanuage on Earth?
The cool thing about Excel is that it's like Function Reactive Programming. When you update the value of a cell, all the other cells that reference to it get updated too. That's pretty cool to have in GUI's as well, and Haskell has that too. See [1]. -chris [1]: http://www.haskell.org/frp/ On 30 Jan, 2007, at 22:46 , Alexy Khrabrov wrote: Heard that statement recently -- that Excel is a functional programming language, and the most used one -- of any programming languages -- on Earth! Is it true? Are there good examples of typical FP style in Excel? Cheers, Alexy ___ 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] Channel9 Interview: Software Composability and theFu ture of Languages
Haskell is _not_ inherently hard - any more than any other programming language. But it is different. So right now, Haskell is hard only because we need more documentation that is designed to make Haskell seem easy. Well, I think it's harder to get a program compiled in Haskell than in Java, for example. It's not too hard, although debugging might be a little difficult. I think this has to do with the type system. Althought it sounds bad, it's actually a good thing. Once you get a Haskell program compiled, chances are much higher that it's correct. You do a bit more work up front, but chances of a bug are way lower. The way I see it, programming in Haskell is an investment. If you're from a OOP-background, some (trivial) things might take a lot more time. But in the end, it does make you more productive. You spend less time tracking bugs, and it's easier to refactor. Not everybody is willing to make an investment when they've got something that works. For example, if you know one imperative language, you can switch to another without taking too much risk. On the other hand, if you switch to a language that is completely different, you don't know if it will get your job done. It doesn't feel safe. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Concurrency in Haskell
Yes, I'm curious too. For example, it would be great if we could change a function that uses map almost automatically to a function that does the map in parallel. Ofcourse it should be in the IO monad, so maybe mapM would be a better choice to start with. -chris On 25 Jan, 2007, at 21:13 , Alexy Khrabrov wrote: What's the state of concurrency in Haskell? If Erlang's main strength is light-weight parallelism, can something like that be done in Haskell? Are there good examples of useful code employing GHC concurrency features one can play with? Cheers, Alexy ___ 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] Currying
what is so great about currying? What are its uses, apart from letting one define functions with less parentheses? Well, from an academic viewpoint, it's very interesting to see a function defined as a composition of functions. From a practical viewpoint, it's just really handy. It saves you a lot of tedious typing, and that's basically what progamming languages are supposed to do. That's exactly what I love about haskell: it saves me from a lot of unnecessary typing. After all, I'm a lazy programmer ;) -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] MissingH: profiler support?
Thanks, this works! I had to build all the other libraries that are required with profiling support too. I also wrote it down on the MissingH wiki, see http://software.complete.org/missingh/wiki/Profiling -chris On 12 Jan, 2007, at 4:08 , Spencer Janssen wrote: The typical way to add profiling support to a Cabal lib is to add - p at configure time (ie runhaskell Setup.hs configure -p). Have you tried this? Cheers, Spencer Janssen On Jan 8, 2007, at 4:13 PM, Chris Eidhof wrote: Hey all, I'm trying to profile my application, which makes use of MissingH. But when compiling with -prof -auto-all, I get the following error: Language.hs:8:7: Could not find module `Data.String': Perhaps you haven't installed the profiling libraries for package MissingH-0.18.0? Use -v to see a list of the files searched for. When compiling without those options, everything works just fine. I built missingh from source, and added -prof -auto-all to GHCPARMS, and did a ./setup configure,make,install and still no result. Does anyone know what could be wrong? I'd really like to keep using MissingH and having profiling support at the same time. Thanks, -chris ___ 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
Resending: [Haskell-cafe] MissingH: profiler support?
Hey, does anyone know about this? Resending as I got no replies (yet) ;) Thanks, -chris On 8 Jan, 2007, at 23:13 , Chris Eidhof wrote: Hey all, I'm trying to profile my application, which makes use of MissingH. But when compiling with -prof -auto-all, I get the following error: Language.hs:8:7: Could not find module `Data.String': Perhaps you haven't installed the profiling libraries for package MissingH-0.18.0? Use -v to see a list of the files searched for. When compiling without those options, everything works just fine. I built missingh from source, and added -prof -auto-all to GHCPARMS, and did a ./setup configure,make,install and still no result. Does anyone know what could be wrong? I'd really like to keep using MissingH and having profiling support at the same time. Thanks, -chris ___ 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] MissingH: profiler support?
Hey all, I'm trying to profile my application, which makes use of MissingH. But when compiling with -prof -auto-all, I get the following error: Language.hs:8:7: Could not find module `Data.String': Perhaps you haven't installed the profiling libraries for package MissingH-0.18.0? Use -v to see a list of the files searched for. When compiling without those options, everything works just fine. I built missingh from source, and added -prof -auto-all to GHCPARMS, and did a ./setup configure,make,install and still no result. Does anyone know what could be wrong? I'd really like to keep using MissingH and having profiling support at the same time. Thanks, -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: SYB and/or HList for XML, deserialization and collections
== Deserialization == HAppS periodically checkpoints application state to disk. Developers may want to add or remove fields from their state types for from data types used by their state types. The current solution is to have the developer assign a version number to state. If state changes then the developer provides dispatch to a deserialization function based on that version number. Well, it is indeed a fact of life that apps get updated, and data- models change. I think Ruby on Rails has implemented this quite good, using migrations. Basically, when you're using a migration, you specify the differences between two datatypes (or in their case, tables). If we found some way to determine those diffs automatically, and then require a function that maps the old types to the new types... but maybe I'm thinking too difficult. Just thinking out loud, really. We could encode the structure of the used datatypes into the state, and let HAppS automatically check if it needs to migrate... One of the concepts that I also like about RoR is that they have 3 modes, development, production and test. Three different databases are used for the three modes, so you're not messing in your production database. Maybe this is something to think about, too. -chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Composing monads (sort of)
Hey Mark, How can I concisely compose these functions without having to write a cascade of case statements such as: case f1 rec1 of Nothing - return Nothing Just id1 - do rec2 - f2 id2 return $ case rec2 of Nothing - return Nothing Just rec2' - case f3 rec2' of I understand that if I was just dealing with Maybe I could use the fact that Maybe is a monad. Yes, you can write like this: id2 - f1 rec1 rec2 - f2 id2 rec3 - f3 rec2 return rec3 or, even shorter: id2 - f1 rec1 rec2 - f2 id2 f3 rec2 The cool thing of the Maybe monad is that it combines a result in such a way that it removes the plumbing of constantly checking for Nothing. I can definitely recommand you the following tutorials: http://www.nomaware.com/monads/html/index.html http://uebb.cs.tu-berlin.de/~magr/pub/Transformers.en.html Those two tutorials really helped me. Good luck, Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
