- Haskell-Cafe - Haskell.org

lhs syntax highlighting in vim
by Eric Stansifer 01 Jul '08

01 Jul '08

Hello, The syntax highlighting file for literate haskell in vim says that its maintainer is haskell-cafe(a)haskell.org, so hopefully one of you will find this relevant. In literate haskell files, vim optionally highlights the non-code text according to TeX markup. The syntax highlighting file looks for key phrases (e.g., "\documentclass") to decide whether to use TeX markup highlighting; but it (erroneously, in my opinion, and at variance with the documentation) will use TeX markup highlighting on any lhs file that contains the '%' character anywhere in it. The bug is in line 74 of version 1.01 of the lhaskell.vim syntax highlighting file. Thanks, Eric

3 2

The ping method in HDBC
by Agent Zhang 01 Jul '08

01 Jul '08

Hi, there I'm wondering if there's a ping method in HDBC that does the same thing as Perl DBI's ping. Please see the following link for details: http://search.cpan.org/~timb/DBI-1.605/DBI.pm#ping I think It's rather important for database auto-connection when preserving database connections for a quite long time in fastcgi applications. Any ideas? Thanks in advance! -agentzh

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http://www.haskell.org/ghc/reportabug
by Galchin, Vasili 01 Jul '08

01 Jul '08

Hi, When I run my test case, I get timer: internal error: scavenge: unimplemented/strange closure type 60 @ 0x76a28400 (GHC version 6.8.2 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug I went to this URL. I already have an account. I want to see if there is a report on this problem but I get the following message ... TICKET_CREATE privileges are required to perform this operation I read some of the Trac documentation but didn't see what privilege I am missing. ?? Thanks, Vasili

4 9

ANN: Hasim, discrete event simulation in Haskell
by Jochem Berndsen 01 Jul '08

01 Jul '08

Hi all, I've started a small project to create a library to do discrete event simulation in Haskell. Its website is located at http://huygens.functor.nl/hasim . It uses monads to define a domain-specific language for "actions" of a process. The interested reader is referred to the website. Regards, -- Jochem Berndsen | jochem(a)functor.nl GPG: 0xE6FABFAB

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re: [Haskell-cafe] Implementing PADS in Haskell?
by David Walker 30 Jun '08

30 Jun '08

Simon writes: > It's not clear to me > > a) whether or not you want new syntax (requires writing a parser) we are starting out our implementation without special syntactic support, but I do anticipate it will be useful primarily because the implementation I envision will need to generate both datastructures and type declarations. I don't quite see how a combinator library, for instance, can do that. For example, it is very nice for the user to declare a pads datatype like this: pdata Pairs = Myints (Pint, /|/, Pint) | Mychars (Pchar, /|/, Pchar) I would hope the effect of such a declaration would be to do two things. First, generate declaration of a Haskell datatype: data Pairs = Myint (int, int) | Mychars (char, char) and second, generate an instance of the GADT (type Pads a where a is the type of the parsed data) that we are planning to use to represent the PADS descriptions. Functions such as parse, print, toxml, etc. perform walks over the GADT instance. eg: Pairs :: Pads Pairs Pairs = ... bunch of constructor applications to build the GADT representing Pairs ... If I just wanted to build the GADT data structure, I can see how I could define a collection of combinators directly in Haskell to do that. However, I want to build a data structure *and* declare a type. And I want programmers to be able to refer to and use both. I do not see how to get around that. In addition, in order to include arbitrary new datatypes in the GADT that we are using to represent pads, it seems necessary to me at the moment to pull a bit of a hack. For each branch of the datatype, I need to wrap up injection and projection from the datatype in a pair of functions and pass that to a generic GADT constructor. Doing that by hand would seem to incur quite a bit of programming overhead and detract from the pleasure of using datatypes. It may be hard to follow what I am talking about... if people were interested, I could post the GADT definition we are working with in a few days when it is a little bit more settled... In addition to the argument about generating type declarations and data structures at the same time, it would seem to me that doing things like being able to put constant literals and regular expressions inline in a custom syntax will improve the readability and useability of the system. However, this argument is not as strong -- it is definitely true of PADS for C and also, I think for O'Caml, but perhaps if we are creative we can figure out a way to fit what we want elegantly into Haskell syntax. > Concerning (b), if you want to write a program that generates one or more Haskell programs, then > Template Haskell is good. But if you can get away with just one program, then you may not > need that extra complexity. Many domain-specific languages embedded in Haskell use just > Haskell (e.g. Parsec, Fran, Yampa...), not TH nor quasiquotation. By the way, when you use the terminology "embedded domain-specific language" is that really just a synonym for "library"? Is there any difference between an "embedded domain-specific language" and an ordinary library? Thanks, Dave PS: it does not look like my email is getting to the Haskell-cafe mailing list, especially from my gmail account. Is the list moderated? Can that cause a delay? Does this list filter email if the reply-to field is different from the sender? My gmail account is princedpw(a)gmail.com with a reply-to of dpw(a)cs.princeton.edu ... I signed up a second time from my princeton account with email address dpw(a)cs.princeton.edu and same reply-to ... -------------- --------------- hi, I sent the message below to the template Haskell mailing list and it was suggested that I send it to the more general Haskell mailing list. After my question, I attached a few responses I have received. Thanks in advance for any suggestions. Dave ------------------------ I am new to Haskell and even more so to Haskell templates -- if there is an obvious answer to my question, please just point me at the relevant URL. Thanks! (If you think I should email this query to a broader Haskell mailing list let me know too.) My friends and I are thinking about adding an extension to Haskell to implement a variant of the PADS domain-specific language. PADS is a convenient syntax to describe a file format and generate a bunch of tools for it such as parser, printer, xml translator, semi-structured query engine, statistical profiler, etc. (We also have tools to automatically infer descriptions from example data but that's not quite the point here.) See www.padsproj.org/ <http://www.padsproj.org/> <http://www.padsproj.org/> for lots more info and examples of PADS for C and PADS for O'Caml. The bottom line question is I'm wondering if I can or should implement my PADS extension using Template Haskell to support the syntactic extensions. If not Template Haskell, is there another Haskell toolkit I should know about? If Template Haskell isn't powerful enough, I'll probably just write a standalone compiler that parses my special syntax and spits out a file full of Haskell declarations (this would be a slight shame because then I would probably not support writing PADS declarations in the midst of other Haskell code). I've looked at simple Template Haskell examples from the Haskell wiki, such as the printf example, but I need to introduce a lot more syntax than that ... What do I need from Template Haskell? Well what I would like to do is add a bit of syntax to Haskell that allows users to define what looks like non-standard type declarations. The "compiler" for these non-standard type declarations will generate a collection of ordinary Haskell declarations that can be used by a programmer. The non-standard typing declarations will be a mixture of what looks like Haskell type declarations, Haskell code, perl-style syntax for regular expressions and perhaps some other stuff I'm not thinking of right now. For example, suppose I want to write a program that converts a file that contains a list of friends into XML (it's a bit of an artificial example so I can illustrate several features): 3 Simon;Peyton Jones John;Launchbury #Phil;Wadler The format starts with a number on the first line to indicate the number of entries in the file. Each line contains one entry which is a first name then a ';' then a last name. Some lines begin with a # -- they are commented out because I'm no longer friends with them. Naturally, Phil Wadler falls into that category. :-) ! The Haskell program I want to write to do this would look something like: ------------------------- {| pdata Line = Comment /#.*/ | Name {first::Pstr /;/, last ::Pstr /\n/} ptype Friends = (x::Pint, |{ x > 0 }|, /\n/, PlistFW x) |} friendsToXML :: String -> XML friendsToXML s = PADSTools.toXML Friends s ------------------------- Notice the following syntactic features: -- {| and |} are delimiters that begin/end pads code (I don't really care what the delimiters are as long as they are relatively concise. For instance, if the delimiters were $( ... ), for instance, that would be fine. -- inside {| and |}, we can jump back into Haskell by using the delimiters |{ and |} -- there are some built-in, pre-defined base types like Pstr (for parsing and printing strings) and Pint (for parsing and printing integers), PlistFW (which takes an argument x to specify the number of elements in the list) -- regular expressions /..../ show up in the middle of what would otherwise be Haskell type declarations -- there is syntax for declaring datatype-like things (introduced by pdata keyword) -- the declarations are dependent types in that there is binding (eg: the x::Pint in the "Friends" type -- the x is bound here) -- variables bound in pads code can then be used in Haskell code nested inside the declaration (eg: the Haskell expression x > 0 refers to the variable x, defined in the outer pads code). -- the outer Haskell code refers to declarations made inside the PADS code. (eg: the Haskell function "friendsToXML s = PADS.Tools.toXML Friends s" refers to Friends, where Friends would be bound to a datastructure generated by the compiler for the pads code. PADSTools is a module defined a priori that contains a number of functions such as toXML, parse, print, query, etc.) Anyway, if you have any comments on how I should handle the syntactic extensions, let me know. Thanks again, Dave ------------ Ian: You can't create new syntax with TH; it's just Haskell (plus the TH syntactic extensions themselves, i.e. $( e ), and a few variants of [| e |]). You'd have to encode the info into Haskell syntax somehow, e.g. something like $( pdata "Line" [C "Comment" [], C "Name" [ ("first", ["Pstr", "/;"]), ... ) or parse them from strings (which isn't nice either, as Haskell doesn't have nice multi-line strings). Thanks Ian ---------------- From Claus Reinke: well, how about using the new quasiquoting to get HereDocs:-) {-# LANGUAGE TemplateHaskell #-} module Here where import Language.Haskell.TH <http://Language.Haskell.TH> <http://Language.Haskell.TH> import Language.Haskell.TH.Quote here :: QuasiQuoter here = QuasiQuoter (litE . stringL) (litP . stringL) then {-# LANGUAGE QuasiQuotes #-} {-# LANGUAGE TemplateHaskell #-} import Here s = [$here| hello multiline world |] test = lines s gives us *Main> test [" \r"," hello\r"," multiline\r"," world\r"," "] Claus ------------------ From Simon Peyton Jones: Dave It's not clear to me a) whether or not you want new syntax (requires writing a parser) b) whether you want a single description to generate multiple different Haskell programs, or just one Concerning (a), as Claus says if you want special purpose syntax (ie not Haskell) then you need quasiquotation. This is only in the HEAD, not a released GHC, but it works reliably as far as I know. http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h… <http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h…> <http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h… <http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h…>> Concerning (b), if you want to write a program that generates one or more Haskell programs, then Template Haskell is good. But if you can get away with just one program, then you may not need that extra complexity. Many domain-specific languages embedded in Haskell use just Haskell (e.g. Parsec, Fran, Yampa...), not TH nor quasiquotation. You'd get a 30x wider audience on the Haskell Cafe mailing list, so yes, I'd try there too. Even jumping to Template Haskell as a solution may be premature; I'm not sure. Meanwhile perhaps other TH folk would like to join in? Simon ______________________________ _________________ Haskell-Cafe mailing list Haskell-Cafe(a)haskell.org <mailto:Haskell-Cafe@haskell.org> http://www.haskell.org/mailman/listinfo/haskell-cafe <http://www.haskell.org/mailman/listinfo/haskell-cafe>

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Fwd: [GHC] #2407: internal error
by Galchin, Vasili 30 Jun '08

30 Jun '08

Hello, Please keep in mind I am only trying to help the Haskell effort. I tried to upload/attach a Linux core file to no avail. Vasili ---------- Forwarded message ---------- From: GHC <trac(a)galois.com> Date: Mon, Jun 30, 2008 at 3:49 AM Subject: [GHC] #2407: internal error To: Cc: glasgow-haskell-bugs(a)haskell.org #2407: internal error --------------------------+------------------------------------------------- Reporter: vigalchin | Owner: Type: bug | Status: new Priority: normal | Component: Compiler Version: 6.8.2 | Severity: normal Keywords: | Testcase: Architecture: Unknown | Os: Linux --------------------------+------------------------------------------------- timer: internal error: resurrectThreads: thread blocked in a strange way (GHC version 6.8.2 for i386_unknown_linux) Please report this as a GHC bug: http://www.haskell.org/ghc/reportabug Aborted (core dumped) -- Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/2407> GHC <http://www.haskell.org/ghc/> The Glasgow Haskell Compiler

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Implementing PADS in Haskell?
by David Walker 30 Jun '08

30 Jun '08

hi, I sent the message below to the template Haskell mailing list and it was suggested that I send it to the more general Haskell mailing list. After my question, I attached a few responses I have received. Thanks in advance for any suggestions. Dave ------------------------ I am new to Haskell and even more so to Haskell templates -- if there is an obvious answer to my question, please just point me at the relevant URL. Thanks! (If you think I should email this query to a broader Haskell mailing list let me know too.) My friends and I are thinking about adding an extension to Haskell to implement a variant of the PADS domain-specific language. PADS is a convenient syntax to describe a file format and generate a bunch of tools for it such as parser, printer, xml translator, semi-structured query engine, statistical profiler, etc. (We also have tools to automatically infer descriptions from example data but that's not quite the point here.) See www.padsproj.org/ <http://www.padsproj.org/> for lots more info and examples of PADS for C and PADS for O'Caml. The bottom line question is I'm wondering if I can or should implement my PADS extension using Template Haskell to support the syntactic extensions. If not Template Haskell, is there another Haskell toolkit I should know about? If Template Haskell isn't powerful enough, I'll probably just write a standalone compiler that parses my special syntax and spits out a file full of Haskell declarations (this would be a slight shame because then I would probably not support writing PADS declarations in the midst of other Haskell code). I've looked at simple Template Haskell examples from the Haskell wiki, such as the printf example, but I need to introduce a lot more syntax than that ... What do I need from Template Haskell? Well what I would like to do is add a bit of syntax to Haskell that allows users to define what looks like non-standard type declarations. The "compiler" for these non-standard type declarations will generate a collection of ordinary Haskell declarations that can be used by a programmer. The non-standard typing declarations will be a mixture of what looks like Haskell type declarations, Haskell code, perl-style syntax for regular expressions and perhaps some other stuff I'm not thinking of right now. For example, suppose I want to write a program that converts a file that contains a list of friends into XML (it's a bit of an artificial example so I can illustrate several features): 3 Simon;Peyton Jones John;Launchbury #Phil;Wadler The format starts with a number on the first line to indicate the number of entries in the file. Each line contains one entry which is a first name then a ';' then a last name. Some lines begin with a # -- they are commented out because I'm no longer friends with them. Naturally, Phil Wadler falls into that category. :-) ! The Haskell program I want to write to do this would look something like: ------------------------- {| pdata Line = Comment /#.*/ | Name {first::Pstr /;/, last ::Pstr /\n/} ptype Friends = (x::Pint, |{ x > 0 }|, /\n/, PlistFW x) |} friendsToXML :: String -> XML friendsToXML s = PADSTools.toXML Friends s ------------------------- Notice the following syntactic features: -- {| and |} are delimiters that begin/end pads code (I don't really care what the delimiters are as long as they are relatively concise. For instance, if the delimiters were $( ... ), for instance, that would be fine. -- inside {| and |}, we can jump back into Haskell by using the delimiters |{ and |} -- there are some built-in, pre-defined base types like Pstr (for parsing and printing strings) and Pint (for parsing and printing integers), PlistFW (which takes an argument x to specify the number of elements in the list) -- regular expressions /..../ show up in the middle of what would otherwise be Haskell type declarations -- there is syntax for declaring datatype-like things (introduced by pdata keyword) -- the declarations are dependent types in that there is binding (eg: the x::Pint in the "Friends" type -- the x is bound here) -- variables bound in pads code can then be used in Haskell code nested inside the declaration (eg: the Haskell expression x > 0 refers to the variable x, defined in the outer pads code). -- the outer Haskell code refers to declarations made inside the PADS code. (eg: the Haskell function "friendsToXML s = PADS.Tools.toXML Friends s" refers to Friends, where Friends would be bound to a datastructure generated by the compiler for the pads code. PADSTools is a module defined a priori that contains a number of functions such as toXML, parse, print, query, etc.) Anyway, if you have any comments on how I should handle the syntactic extensions, let me know. Thanks again, Dave ------------ Ian: You can't create new syntax with TH; it's just Haskell (plus the TH syntactic extensions themselves, i.e. $( e ), and a few variants of [| e |]). You'd have to encode the info into Haskell syntax somehow, e.g. something like $( pdata "Line" [C "Comment" [], C "Name" [ ("first", ["Pstr", "/;"]), ... ) or parse them from strings (which isn't nice either, as Haskell doesn't have nice multi-line strings). Thanks Ian ---------------- From Claus Reinke: well, how about using the new quasiquoting to get HereDocs:-) {-# LANGUAGE TemplateHaskell #-} module Here where import Language.Haskell.TH <http://Language.Haskell.TH> import Language.Haskell.TH.Quote here :: QuasiQuoter here = QuasiQuoter (litE . stringL) (litP . stringL) then {-# LANGUAGE QuasiQuotes #-} {-# LANGUAGE TemplateHaskell #-} import Here s = [$here| hello multiline world |] test = lines s gives us *Main> test [" \r"," hello\r"," multiline\r"," world\r"," "] Claus ------------------ From Simon Peyton Jones: Dave It's not clear to me a) whether or not you want new syntax (requires writing a parser) b) whether you want a single description to generate multiple different Haskell programs, or just one Concerning (a), as Claus says if you want special purpose syntax (ie not Haskell) then you need quasiquotation. This is only in the HEAD, not a released GHC, but it works reliably as far as I know. http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h… <http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h…> Concerning (b), if you want to write a program that generates one or more Haskell programs, then Template Haskell is good. But if you can get away with just one program, then you may not need that extra complexity. Many domain-specific languages embedded in Haskell use just Haskell (e.g. Parsec, Fran, Yampa...), not TH nor quasiquotation. You'd get a 30x wider audience on the Haskell Cafe mailing list, so yes, I'd try there too. Even jumping to Template Haskell as a solution may be premature; I'm not sure. Meanwhile perhaps other TH folk would like to join in? Simon

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implementing PADS in Haskell?
by David Walker 30 Jun '08

30 Jun '08

hi, I sent the message below to the template Haskell mailing list and it was suggested that I send it to the more general Haskell mailing list. After my question, I attached a few responses I have received. Thanks in advance for any suggestions. Dave ------------------------ I am new to Haskell and even more so to Haskell templates -- if there is an obvious answer to my question, please just point me at the relevant URL. Thanks! (If you think I should email this query to a broader Haskell mailing list let me know too.) My friends and I are thinking about adding an extension to Haskell to implement a variant of the PADS domain-specific language. PADS is a convenient syntax to describe a file format and generate a bunch of tools for it such as parser, printer, xml translator, semi-structured query engine, statistical profiler, etc. (We also have tools to automatically infer descriptions from example data but that's not quite the point here.) See www.padsproj.org/ for lots more info and examples of PADS for C and PADS for O'Caml. The bottom line question is I'm wondering if I can or should implement my PADS extension using Template Haskell to support the syntactic extensions. If not Template Haskell, is there another Haskell toolkit I should know about? If Template Haskell isn't powerful enough, I'll probably just write a standalone compiler that parses my special syntax and spits out a file full of Haskell declarations (this would be a slight shame because then I would probably not support writing PADS declarations in the midst of other Haskell code). I've looked at simple Template Haskell examples from the Haskell wiki, such as the printf example, but I need to introduce a lot more syntax than that ... What do I need from Template Haskell? Well what I would like to do is add a bit of syntax to Haskell that allows users to define what looks like non-standard type declarations. The "compiler" for these non-standard type declarations will generate a collection of ordinary Haskell declarations that can be used by a programmer. The non-standard typing declarations will be a mixture of what looks like Haskell type declarations, Haskell code, perl-style syntax for regular expressions and perhaps some other stuff I'm not thinking of right now. For example, suppose I want to write a program that converts a file that contains a list of friends into XML (it's a bit of an artificial example so I can illustrate several features): 3 Simon;Peyton Jones John;Launchbury #Phil;Wadler The format starts with a number on the first line to indicate the number of entries in the file. Each line contains one entry which is a first name then a ';' then a last name. Some lines begin with a # -- they are commented out because I'm no longer friends with them. Naturally, Phil Wadler falls into that category. :-) ! The Haskell program I want to write to do this would look something like: ------------------------- {| pdata Line = Comment /#.*/ | Name {first::Pstr /;/, last ::Pstr /\n/} ptype Friends = (x::Pint, |{ x > 0 }|, /\n/, PlistFW x) |} friendsToXML :: String -> XML friendsToXML s = PADSTools.toXML Friends s ------------------------- Notice the following syntactic features: -- {| and |} are delimiters that begin/end pads code (I don't really care what the delimiters are as long as they are relatively concise. For instance, if the delimiters were $( ... ), for instance, that would be fine. -- inside {| and |}, we can jump back into Haskell by using the delimiters |{ and |} -- there are some built-in, pre-defined base types like Pstr (for parsing and printing strings) and Pint (for parsing and printing integers), PlistFW (which takes an argument x to specify the number of elements in the list) -- regular expressions /..../ show up in the middle of what would otherwise be Haskell type declarations -- there is syntax for declaring datatype-like things (introduced by pdata keyword) -- the declarations are dependent types in that there is binding (eg: the x::Pint in the "Friends" type -- the x is bound here) -- variables bound in pads code can then be used in Haskell code nested inside the declaration (eg: the Haskell expression x > 0 refers to the variable x, defined in the outer pads code). -- the outer Haskell code refers to declarations made inside the PADS code. (eg: the Haskell function "friendsToXML s = PADS.Tools.toXML Friends s" refers to Friends, where Friends would be bound to a datastructure generated by the compiler for the pads code. PADSTools is a module defined a priori that contains a number of functions such as toXML, parse, print, query, etc.) Anyway, if you have any comments on how I should handle the syntactic extensions, let me know. Thanks again, Dave ------------ Ian: You can't create new syntax with TH; it's just Haskell (plus the TH syntactic extensions themselves, i.e. $( e ), and a few variants of [| e |]). You'd have to encode the info into Haskell syntax somehow, e.g. something like $( pdata "Line" [C "Comment" [], C "Name" [ ("first", ["Pstr", "/;"]), ... ) or parse them from strings (which isn't nice either, as Haskell doesn't have nice multi-line strings). Thanks Ian ---------------- >From Claus Reinke: well, how about using the new quasiquoting to get HereDocs:-) {-# LANGUAGE TemplateHaskell #-} module Here where import Language.Haskell.TH import Language.Haskell.TH.Quote here :: QuasiQuoter here = QuasiQuoter (litE . stringL) (litP . stringL) then {-# LANGUAGE QuasiQuotes #-} {-# LANGUAGE TemplateHaskell #-} import Here s = [$here| hello multiline world |] test = lines s gives us *Main> test [" \r"," hello\r"," multiline\r"," world\r"," "] Claus ------------------ >From Simon Peyton Jones: Dave It's not clear to me a) whether or not you want new syntax (requires writing a parser) b) whether you want a single description to generate multiple different Haskell programs, or just one Concerning (a), as Claus says if you want special purpose syntax (ie not Haskell) then you need quasiquotation. This is only in the HEAD, not a released GHC, but it works reliably as far as I know. http://www.haskell.org/ghc/dist/current/docs/users_guide/template-haskell.h… Concerning (b), if you want to write a program that generates one or more Haskell programs, then Template Haskell is good. But if you can get away with just one program, then you may not need that extra complexity. Many domain-specific languages embedded in Haskell use just Haskell (e.g. Parsec, Fran, Yampa...), not TH nor quasiquotation. You'd get a 30x wider audience on the Haskell Cafe mailing list, so yes, I'd try there too. Even jumping to Template Haskell as a solution may be premature; I'm not sure. Meanwhile perhaps other TH folk would like to join in? Simon

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Re: [Haskell-cafe] http://www.haskell.org/ghc/reportabug
by Isaac Dupree 30 Jun '08

30 Jun '08

Galchin, Vasili wrote: > Isaac, > > which "different trac page"? I have tried several times to no avail! any one that says you're not logged in. Probably you're having a different problem than I was, if it's that hard to solve... -Isaac

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[Haskell-cafe] Re: blas bindings, why are they so much slower the C?
by patperry＠stanford.edu 30 Jun '08

30 Jun '08

Thanks for the patch, Don. I'm on vacation now, but I'll apply it when I get back. As for why "getDot" involves pattern matching, it is because a vector is either a pointer to raw storage, or a conjugated vector. I wrote a blog post about this for those of you who are interested ( http://quantile95.com/2008/06/12/blas-data-types/ ). The current data type is this: data DVector t n e = DV { fptr :: !(ForeignPtr e) , offset :: !Int , len :: !Int , stride :: !Int } | C !(DVector t n e) Now, it isn't strictly necessary to use an algebraic data type-- I could have just used a boolean flag, but the code is a little cleaner this way. I haven't done any tests to see what the difference in performance is. I would expect that a pattern match between two alternatives would be just as fast as checking a boolean flag. The good news is that this is a constant-time overhead. For larger vectors, getDot should approach the performance of a raw cblas_ddot call. Patrick

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Haskell Related Reading
by Darrin Thompson 30 Jun '08

30 Jun '08

I have a trip coming up and might have some reading time. I was hoping to get through some of the classics, bananas and lenses, the essence, etc. So I have a few questions: Bananas and lenses et. al. uses some notation that I don't understand right out of the gate. Is there a good primer on whatever that brand of double bars and arrows means? The essense of functional programming looks good, I could understand it when I skimmed it but can I print it out on US letter? The PDF at citeseer was aligned badly. (Essece seemed like a fabulous intro or chapter 2 on getting used to monads. Better than most stuff on the web. Funny that...) I'm also interested in FRP as it might relate to web programming. Anyone have a recommendation? -- Darrin

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Ptr Word8 display question
by Galchin, Vasili 29 Jun '08

29 Jun '08

Hi, Suppose I have a value of type Ptr Word8 and also an Int which is the length of the Ptr Word8(sorry if I am thinking too much in a C string frame of mind). How can I display the Ptr Word8 value of the given length? Vasili

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Learning GADT types to simulate dependent types
by Paul Johnson 29 Jun '08

29 Jun '08

I'm trying to understand how to use GADT types to simulate dependent types. I'm trying to write a version of list that uses Peano numbers in the types to keep track of how many elements are in the list. Like this: {-# OPTIONS -fglasgow-exts -fallow-undecidable-instances #-} module Plist where infixr 3 :| data Zero data S a class Add n1 n2 t | n1 n2 -> t, n1 t -> n2 instance Add Zero n n instance Add (S n1) n2 (S t) data Plist n a where Nil :: Plist Zero a (:|) :: a -> Plist n a -> Plist (S n) a instance (Show a) => Show (Plist n a) where show Nil = "Nil" show (x :| xs) = show x ++ " :| " ++ show xs pHead :: Plist (S n) a -> a pHead (x :| _) = x pTail :: Plist (S n) a -> Plist n a pTail (_ :| xs) = xs pConcat Nil ys = ys pConcat (x :| xs) ys = x :| pConcat xs ys Everything works except the last function (pConcat). I figured that it should add the lengths of its arguments together, so I created a class Add as shown in the Haskell Wiki at http://www.haskell.org/haskellwiki/Type_arithmetic. But now I'm stuck. When I try to load this module I get: Plist.hs:32:8: GADT pattern match in non-rigid context for `Nil' Tell GHC HQ if you'd like this to unify the context In the pattern: Nil In the definition of `pConcat': pConcat Nil ys = ys Failed, modules loaded: none. (Line 32 is "pConcat Nil ys = ys") So how do I do this? Am I on the right track? Can someone help improve my Oleg rating? Thanks, Paul.

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Galois move complete, Hackage back online
by Don Stewart 29 Jun '08

29 Jun '08

Galois has completed the move of its data center, and the services: hackage.haskell.org darcs.haskell.org are now back online. Thanks for your patience, everyone! Enjoy the new bandwidth. -- Don

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Hackage
by Cetin Sert 29 Jun '08

29 Jun '08

Hi, Hackage seems to have been down for a few days now. When is it going to be back online? It is not possible to darcs-get any packages either. Best Regards, Cetin Sert

1 0

blas bindings, why are they so much slower the C?
by Anatoly Yakovenko 28 Jun '08

28 Jun '08

here is the C: #include <cblas.h> #include <stdlib.h> int main() { int size = 1024; int ii = 0; double* v1 = malloc(sizeof(double) * (size)); double* v2 = malloc(sizeof(double) * (size)); for(ii = 0; ii < size*size; ++ii) { double _dd = cblas_ddot(0, v1, size, v2, size); } free(v1); free(v2); } this is the haskell: module Main where import Data.Vector.Dense.IO main = do let size = 1024 v1::IOVector Int Double <- newListVector size [0..] v2::IOVector Int Double <- newListVector size [0..] mapM_ (\ ii -> do v1 `getDot` v2) [0..size*size] time ./testdot real 0m0.017s user 0m0.010s sys 0m0.010s time ./htestdot real 0m4.692s user 0m4.670s sys 0m0.030s so like 250x difference htestdot.prof is no help Tue Jun 17 20:46 2008 Time and Allocation Profiling Report (Final) htestdot +RTS -p -RTS total time = 3.92 secs (196 ticks @ 20 ms) total alloc = 419,653,032 bytes (excludes profiling overheads) COST CENTRE MODULE %time %alloc main Main 88.3 83.0 CAF Main 11.7 17.0 individual inherited COST CENTRE MODULE no. entries %time %alloc %time %alloc MAIN MAIN 1 0 0.0 0.0 100.0 100.0 CAF Main 216 7 11.7 17.0 100.0 100.0 main Main 222 1 88.3 83.0 88.3 83.0 CAF GHC.Float 187 1 0.0 0.0 0.0 0.0 CAF GHC.Handle 168 3 0.0 0.0 0.0 0.0

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ghci vi mode?
by Adam Smyczek 28 Jun '08

28 Jun '08

If I remember correctly, ghci uses readline framework on Linux/OS X. Is it possible to change ghci editing mode to vi? Thanks, Adam

2 1

Error in configure script for GHC
by Jefferson Heard 28 Jun '08

28 Jun '08

I've tried all the 6.6 and 6.8 versions, trying to compile them on a RHEL-based supercomputer, and I always see this error when I run ./configure: -bash-3.00$ ./configure checking build system type... x86_64-unknown-linux-gnu checking host system type... x86_64-unknown-linux-gnu checking target system type... x86_64-unknown-linux-gnu Which we'll further canonicalise into: x86_64-unknown-linux checking for path to top of build tree... pwd: timer_create: Invalid argument configure: error: cannot determine current directory Is this a known bug with GHC, or is it my supercomputer? We have several supercomputers here running in production, so I can't really ask them to change the configuration just for me, but nonetheless I'd like to run on them.

3 4

Call Graph Tool?
by C.M.Brown 28 Jun '08

28 Jun '08

Hi, I have approx. 100+ source files and I was wondering if anyone has a tool that would let me see a visual call graph for the source files; i.e. a visual hierarchy of which module is imported by what, and so forth. Kind regards, Chris.

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what's up with hackage.haskell.org?
by Martin DeMello 28 Jun '08

28 Jun '08

haven't been able to get to it in a couple of days (at least) martin

2 2

Parsing problem
by Eric 28 Jun '08

28 Jun '08

Hi all, I'm using the Parsec library to parse the following grammar expr = atom+ atom = integer | var | (expr) The input to the parser is a list of (Token, SourcePos). I have the following code for atom: atom = try variable <|> try integerr <|> do{sat(== Reserved "("); (e,pos) <- expression; sat(==Reserved ")"); return (e,pos)} sat p = do (t,pos) <- item if p t then return(t,pos) else pzero When I run the code on the input "(_ineg_ 0)" the parser fails, but removing sat(==Reserved ")") and it succeeds. Can any one see why? E.

2 7

System.Console.Readline stifleHistory Question
by Daniel Kahlenberg 27 Jun '08

27 Jun '08

Hello all, I'm learning Haskell and so very likely will have advantages from the history persistence feature added to the ghci haskell interpreter. It drives very well in my setup (the history file is growing and used), but I wanted to increase the number of saved history entries and now my question concerning ghci: In the ticket (http://hackage.haskell.org/trac/ghc/ticket/2050) associated with the feature, there's written that one can call stifleHistory in its dotghci file. Have done it like: :m +System.Console.Readline stifleHistory 300 :m -System.Console.Readline but now my ghci.exe says: Could not find module `System.Console.Readline': Use -v to see a list of the files searched for. <interactive>:1:0: Not in scope: `stifleHistory' `uname -r`: MINGW32_NT-5.1 CLE10 1.0.11(0.46/3/2) 2007-01-12 12:05 i686 Msys Do you have an idea, where I'm wrong? I'm starting my ghci session from zsh shell, provided by cygwin, wrapped in a tty emulator: $Drive\puttycyg\putty.exe -cygterm $Drive\zsh\bin\zsh.exe -p -c 'PATH=/cygdrive/h/zsh/bin:$PATH HOME=/cygdrive/h/.homedir rlwrap $(which ghcii.sh) -package-conf $Drive/.homedir/ghc/i386-mingw32-6.8.3/package.conf -read-dot-ghci' So I did not expect Readline not to work, but maybe the ghc system only sees the result from `uname -r` above?? Bye, Daniel.

1 1

Fwd: Stack Overflow with HaXml
by Samuel Silva 27 Jun '08

27 Jun '08

Hello I presents a small case studie, when I was using HaXml with DtdToHaskell. I write small DTD: > <!ELEMENT top (#PCDATA|child)* > > <!ELEMENT child (#PCDATA) > I run DtdToHaskell small.DTD > Extsubext.hs and test it with small XML > <top><child></child></top> Result it is presented below: >$ ghci Extsubset.hs >GHCi, version 6.8.2: http://www.haskell.org/ghc/ :? for help >Loading package base ... linking ... done. >[1 of 1] Compiling Extsubset ( Extsubset.hs, interpreted ) >Ok, modules loaded: Extsubset. >*Extsubset> fReadXml "sample.xml" :: IO Top >Loading package array-0.1.0.0 ... linking ... done. >Loading package bytestring-0.9.0.1 ... linking ... done. >Loading package pretty-1.0.0.0 ... linking ... done. >Loading package old-locale-1.0.0.0 ... linking ... done. >Loading package old-time-1.0.0.0 ... linking ... done. >Loading package filepath-1.1.0.0 ... linking ... done. >Loading package directory-1.0.0.0 ... linking ... done. >Loading package random-1.0.0.0 ... linking ... done. >Loading package process-1.0.0.0 ... linking ... done. >Loading package haskell98 ... linking ... done. >Loading package polyparse-1.1 ... linking ... done. >Loading package containers-0.1.0.1 ... linking ... done. >Loading package HaXml-1.19.4 ... linking ... done. >*** Exception: stack overflow >*Extsubset> HaXml is able handle XML mixed elements? -- Don't hug that, Hugs ME! Samuel Silva

1 0

Haskell, Microsoft, and interview questions
by Andrew Wagner 27 Jun '08

27 Jun '08

This post borders on being off-topic, but it seems like people on this list would be interested. First, some of you know that I had the distinct privilege of flying out to Microsoft this week to interview for a Software Development Engineer position on their Live Search team. So I want to first tell you about their reaction to my Haskell experience, and then give you some interesting coding problems that they asked me to solve, which could be good practice to tackle in Haskell. So the first task I was given to do, long before my in-person interview, was to complete a technical assessment. This consisted of two fairly simple algorithms to write. I chose to do so in Haskell. On the basis of this assessment, they decided I was worth a phone interview. When I got on that interview, one of the first things the interviewer said was "So, one thing that jumped out immediately was that you did the assessment in Haskell. Tell me a little bit about that." It led to a good discussion about why I like Haskell and functional programming. When I actually flew out there, several people made comments about me being "that guy who writes Haskell". The recruiter even said something along the lines of "anyone who knows haskell is certainly worth our time to talk to." Moral of the story: Haskell rocks, and even Microsoft knows it! That said, here are some interesting problems to work through in Haskell, if you'd like: 1.) A "rotated array" is an array of integers in ascending order, after which for every element i, it has been moved to element (i + n) mod sizeOfList. Write a function that takes a rotated array and, in less-than-linear time, returns n (the amount of rotation). 2.) You are given a list of Ball objects. Each Ball is either Red or Blue. Write a function that partitions these balls so that all of the balls of each color are contiguous. Return the index of the first ball of the second color (your result can be Red balls, then Blue balls, or the other way around). In haskell, you'll probably want to return a ([Ball],Int). 3.) Live Search is a search engine. Suppose it was to be tied into an online store. Now you're given two lists. One is a [(SessionId, NormalizedQuery)]. That is, when a particular user performs a query, it is turned into some consistent format, based on their apparent intent, and stored in this logfile. The second list is a [(SessionId, ProductId)]. This indicates the product bought by a particular user. Now, you want to take these two (potentially very long) lists, and return some structure that will make it easy to take a query and return a list of the most popular resulting purchases. That is, of people who have run this query in the past, what are the most common products they've wound up buying? The interviewer said that this is an instance of a well-known problem, but I didn't catch the name of it. 4.) You're given an array which contains the numbers from 1 to n, in random order, except there is one missing. Write a function to return the missing number. 5.) Write a function to reconstruct a binary tree from its preorder traversal and inorder traversal. Take into account that the traversals could be invalid. 6.) You have a [(WeatherStationId, Latitude, Longitude)]. Similar to #3, write a function which will, off-line, turn this into a data structure from which you can easily determine the nearest Weather Station, given an arbitrary Latitude and Longitude. 7.) Write a function for scoring a mastermind guess. That is, in a game of mastermind (http://en.wikipedia.org/wiki/Mastermind_(board_game)) given a guess, and the actual answer, determine the number correct, the number wrong, and the number out of place. 8.) Implement a trie (http://en.wikipedia.org/wiki/Trie) data structure. Write a function add, which takes a word, and a trie, and adds the word to the trie. Write another function lookup, which takes a prefix and a trie, and returns all the words in the trie that start with that prefix. 9.) Write an algorithm to shuffle a deck of cards. Now write a function to perform some kind of evaluation of "how shuffled" a deck of cards is. Hope you enjoy!

6 9

haskell and dockapps
by Martin DeMello 27 Jun '08

27 Jun '08

Anyone written a windowmaker dockapp in Haskell? I thought it'd be a fun project, but I don't quite know where to start. martin

2 2

Internet Communications Engine and Haskell
by Mitar 27 Jun '08

27 Jun '08

Hi! Has been any work on implementing Internet Communications Engine in Haskell already done? Any other suggestions how could I use ICE in Haskell? Through FFI calls to its C++ version? http://www.zeroc.com/ice.html Mitar

2 1

hxt and pickler combinations
by Andrea Rossato 27 Jun '08

27 Jun '08

Hello, I'm using HXT for writing a Citation Style Language (http://xbiblio.sourceforge.net) implementation in Haskell and I'm trying to use the hxt pickler library to parse XML data contained in elements that can be interleaved, that is to say, elements that can appear in any order within other elements. For instance: <data> <string>ciao</string> <int>2</int> </data> or <data> <int>2</int> <string>ciao</string> </data> are both permitted. I'm not able to write picklers able to parse such kind of data. I indeed noticed that this is not possible with interleaved elements, but it is possible with attributes. To make myself hopefully clearer I included some code below. Suppose we have a data structure like: data Term = T Int String deriving ( Show ) If encoded in XML without respecting the ordering (first the Int and then the String), picklers seem to fail. But if I use attributes to store the values, this doesn't happen. In other word, the xp1 pickler (taken from the example below) will fail with such an xml doc: <data> <string>ciao</string> <int>2</int> </data> since it requires the 'int' element to appear before the 'string' element. To test this behaviour, run the code below and see that: - test doc1 xp1 will fail - test doc2 xp1 will succeed while: - test doc3 xp2 will succeed - test doc4 xp2 will succeed What am I getting wrong? It's just a matter of wrong combinator I'm choosing or I'm getting wrong something more fundamental? TIA. Andrea The code: import Text.XML.HXT.Arrow test :: String -> PU Term -> IO () test t xp = do p <- runX ( constA t >>> xread >>> xunpickleVal xp ) putStrLn (show p) data Term = T Int String deriving ( Show ) xp1, xp2 :: PU Term xp1 = xpElem "data" $ xpWrap (uncurry T, \(T i s) -> (i, s)) $ xpPair (xpElem "int" xpickle) (xpElem "string" xpText ) xp2 = xpElem "data" $ xpWrap (uncurry T, \(T i s) -> (i, s)) $ xpPair (xpAttr "int" xpickle) (xpAttr "string" xpText ) doc1, doc2, doc3, doc4 :: String doc1 = "<data><string>ciao</string><int>2</int></data>" doc2 = "<data><int>2</int><string>ciao</string></data>" doc3 = "<data int=\"2\" string=\"ciao\" />" doc4 = "<data string=\"ciao\" int=\"4\" />"

1 1

ghc-HEAD: build succeeds, but install fails with linker errors?
by Reid Barton 26 Jun '08

26 Jun '08

I'm trying to install GHC from the darcs repository for the first time, so I'm hoping someone here can tell me if I'm doing something wrong before I bother cvs-ghc. I'm currently running ghc 6.8.2 on Debian x86 Linux. Following the instructions on the wiki, I put the following in a file and ran it: #!/bin/bash darcs get --partial http://darcs.haskell.org/ghc cd ghc chmod +x darcs-all ./darcs-all get sh boot ./configure --prefix=$HOME/ghc-HEAD make make install but during the "make install" step I get the error ../../compiler/stage1/ghc-inplace -no-user-package-conf -o ghc-pkg.bin -H32m -O -cpp -Wall -fno-warn-name-shadowing -fno-warn-unused-matches -package Cabal -Rghc-timing -package unix -package containers Main.o Version.o CRT_noglob.o Main.o: In function `s7AP_info': (.text+0x1d): undefined reference to `prettyzm1zi0zi0zi0_TextziPrettyPrintziHughesPJ_Str_con_info' {- hundreds of similar errors (not all from the pretty package, some from base and others as well) -} collect2: ld returned 1 exit status <<ghc: 50428432 bytes, 6 GCs, 131072/131072 avg/max bytes residency (1 samples), 31M in use, 0.00 INIT (0.00 elapsed), 0.07 MUT (0.55 elapsed), 0.02 GC (0.02 elapsed) :ghc>> make[2]: *** [ghc-pkg.bin] Error 1 Failed making install in ghc-pkg: 1 make[1]: *** [install] Error 1 make: *** [install] Error 1 Have I got some of the steps wrong? Regards, Reid Barton

3 2

Access to Oracle database from Haskell
by Henning Thielemann 26 Jun '08

26 Jun '08

Is there a way of accessing a remote Oracle database by one of the common Haskell database interfaces (HaskellDB, Takusen, etc.) ? I tried to get unixODBC and Oracle's Instant Client running on a Linux machine, but I'm trapped in the notorious error: $ isql USER -v [IM004][unixODBC][Driver Manager]Driver's SQLAllocHandle on SQL_HANDLE_HENV failed [ISQL]ERROR: Could not SQLConnect This error message is discussed in various web forums, but there seems to be no systematic way to track down the problem. So I wonder whether there is another way to access the Oracle data base from Haskell.

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Stupid question about Cabal file
by Fernand 26 Jun '08

26 Jun '08

Hi, Excuse me in advance if this is a trivial question, but I have been unable to find (understand?) the answer in Cabal's documentation. My issue is simple : I build a Cabal package named, let's say, "foo". That package is a library (libHSfoo.a, something like that), which exposes its Foo.Bar and Foobar modules. I wrote the cabal file, register it, everything seems fine. The issue comes when I try to use that package when compiling a main program, like this : ghc -package foo MyMain.hs [other options] I get an error about the compiler not finding the interface files Foobar.hi and Bar.hi, as I have "import Bar" and "import Foo.Bar" in my "MyMain.hs" file. Of course, I could add "-l" flags to point to the ".hi" files that I used to compile my package, but I get the well-known issue about the fact that the package's names of the interface files (which were compiled with the "-package-name foo" option) are not the correct ones ("Bad interface file: ../foo/Foobar.hi, Something is amiss; requested module main:Foobar differs from name found in the interface file foo:Foobar") ; and that solution is ugly anyway. So far, I found some Cabal documentation talking about the import-dirs property, but I did not manage to "make it work", I mean, my package does not seems to "include" the interface files. I am sure, on the other hand, that it is possible :) Sincerely yours, Fernand

2 4

history of tuples vs pairs
by Conal Elliott 26 Jun '08

26 Jun '08

I have a foggy memory that early ML had only binary pairing, nesting for n-tuples. Can anyone confirm this memory. If so, does anyone remember the rationale for going to n-tuples? Performance, perhaps? Similarly, did the Haskell designers consider pairs as an alternative to n-ary tuples? The reason I ask is that while ghc and libraries suppors n-tuples for some values of n, the support is generally incomplete and inconsistent. And some abstractions are very heavily biased toward pairing, particularly Arrow and the pair instances of Monad and Applicative. And of course, inclusion of fst and snd in the prelude but lack of similar standard functions for n-tuples with n>2. - Conal

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looking for advice on "lifting" and FFI
by Galchin, Vasili 26 Jun '08

26 Jun '08

Hello, I am thinking about "glue"/"binding" code for POSIX listio and aio_suspend. E.g. http://docs.hp.com/en/B9106-90009/lio_listio.2.html 1) It seems to me that this is a "lifting" problem where we lift to a Haskell list of "aiocb's" to a C array of pointers?? An example of the "C array of pointers" is described by http://docs.hp.com/en/B9106-90009/lio_listio.2.html 2) Is it reasonable for the domain of the 1) mapping to be a Haskell list of "aiocb's"?? Kind regards, Vasili

1 0

Haskell Weekly News: Issue 74 - June 25, 2008
by Brent Yorgey 26 Jun '08

26 Jun '08

--------------------------------------------------------------------------- Haskell Weekly News http://sequence.complete.org/hwn/20080625 Issue 74 - June 25, 2008 --------------------------------------------------------------------------- Welcome to issue 74 of HWN, a newsletter covering developments in the [1]Haskell community. This week, you'll notice a bit more detail in the 'Blogs' section. I've added summaries to some of the posts, to help you decide which you might be interested to read (only a few this week, since I added them at the last minute). I've also >>> highlighted blogs not syndicated on Planet Haskell---mostly people who have just begun learning Haskell and decided to blog about it. Go show them some comment love, and invite them into the community! Community News Andrew Wagner (chessguy) recently flew out to Microsoft for an interview with their Live Search team. In [2]an email to the cafe, he shares some stories from his experience and some interesting coding challenges. Announcements HAppS self-demoing tutorial. Thomas Hartman [3]announced a self-demoing, HStringTemplate-using intro to HAppS. Check out the [4]live demo or obtain it [5]from Hackage. NWFP Interest Group. Greg Meredith [6]announced the next monthly meeting of the NW Functional Programmers Interest group, 6:30 on June 25 at the Seattle Public Library. Greg will talk about a very cool [7]compositional representation of graphs he's been tinkering with recently. ICFP final call for posters. Matthew Fluet [8]announced the final call for proposals for the ICFP 2008 poster session, which should be [9]submitted by June 30. Let people know what you're working on! type-level and parameterized-data packages. Alfonso Acosta [10]announced the release of the [11]type-level and parameterized-data packages, which provide type-level computation and parameterized types a la a dependently-typed system. Lambda in the sun. James Iry [12]announced the creation of [13]Southern California Functional Programmers (SoCalFP), a group for people in LA, Orange County, and San Diego to meet to discuss, debate, present, and learn about functional programming concepts and techniques in various languages. Real World Haskell. Bryan O'Sullivan [14]announced the availability of ten new draft chapters of [15]Real World Haskell, the upcoming O'Reilly book being written by Bryan, John Goerzen, and Don Stewart. In case you were worried, yes, you'll be able to have one in your Christmas stocking! Pugs on hackage!. Audrey Tang has uploaded to Hackage [16]version 6.2.13.2 of [17]Pugs, an implementation of Perl 6 in Haskell. Literal programming with rst-literals. Martin Blais [18]described a neat use of his utility [19]rst-literals to extract Haskell code from ReST documents, enabling a different style of literate programming. Pipe 1.0. Matti Niemenmaa [20]announced the release of [21]Pipe, a library for piping data through a pipeline of processes. HUnit. Richard Giraud [22]announced that he has improved the HUnit documentation and published the changes in a [23]darcs repository. hback. Norbert Wojtowicz [24]announced a new release of [25]hback, a Haskell implementation of the [26]dual n-back memory game using [27]gtk2hs. Google Summer of Code Progress updates from participants in the 2008 [28]Google Summer of Code. Hoogle 4. Neil Mitchell (ndm) is working on Hoogle 4, and recently [29]added two new features, multi-word search and intelligent suggestions. DPH physics engine. Roman Cheplyaka (Feuerbach) is working on a physics engine using [30]Data Parallel Haskell. [31]This week he intended to implement simple ad-hoc cubic collision geometry to test collisions with rotation, but the code became too cumbersome and non-extensible. He took a break to read some papers, and found [32]a better solution. GHC plugins. Max Bolingbroke is working on dynamically loaded plugins for GHC. [33]This week he worked on adding arbitrary user-specified phases to GHC, implementing a control system, pipeline generation, and [34]Template Haskell integration. Next he plans to work on a plugin annotation system. Cabal dependency framework. Andrea Vezzosi (Saizan) is working on a make-like dependency analysis framework for Cabal. He has posted [35]a detailed explanation of his project, some of the issues involved, and his progress so far. Language.C. Benedikt Huber (visq) is working on Language.C, a standalone parser/pretty printer library for C99. This week he worked on AST documentation and improvements, prepared to port the AST analysis from c2hs, and worked on the pretty printer's internals. Generic tries. Jamie Brandon is working on a library for efficient maps using generalized tries. Recently he has worked on implementing some [36]bitpacking tools to save memory. GHC API. Thomas Schilling (nominolo) is supposedly working on [37]improvements to the GHC API. However, officials at HWN headquarters have begun privately speculating that Thomas does not, in fact, exist. Discussion history of tuples vs pairs. Conal Elliott [38]asked about the history of support for n-tuples in Haskell and ML. hackageDB maintainer policy. Ross Paterson began a lengthy [39]discussion towards agreeing on a policy for uploading packages to Hackage, specifying whether the package is maintained and who is maintaining it, and other related issues. What is a rigid type variable?. Xiao-Yong Jin [40]asked what the 'rigid type variables' are that are sometimes referred to in GHC error messages. Read the thread for a concise discussion and the solution to the original problem. Map interface. Jamie Brandon started a [41]thread asking for feedback on his proposed API for generic tries, and the discussion is still ongoing. Left and right folds. George Kangas [42]exhibited a pair of very elegant alternate definitions for left and right fold, and showed how this alternate viewpoint makes obvious several algebraic identities as well as the generalization to [43]Data.Foldable. A must-read for the aspiring functional programmer. ribbonsPerLine. Alfonso Acosta asked an interesting [44]question about "ribbonsPerLine" in the Text.PrettyPrint.HughesPJ library. Do you know what it does? The answer can be found in the [45]original paper describing the library. Jobs PhD position at University of Strathclyde, Glasgow. Simon Marlow [46]announced, on behalf of Patricia Johann, an open PhD position in operational and categorical approaches to parametricity. The funded position is in the newly-formed Mathematically Structured Programming group at the University of Strathclyde, comprising Neil Ghani, Patricia Johann, and Conor McBride. Quantitative Trading Developer Position at Hutchin Hill Capital. Neil Mehra [47]announced an open position for a Quantitative Trading Developer at Hutchin Hill Capital, a newly formed multi-strategy hedge fund located in midtown Manhattan. Blog noise [48]Haskell news from the [49]blogosphere. * >>> Blockcipher: [50]Converting Geospatial Coordinates. Blockcipher has had enough of reading Haskell tutorials, and is itching to actually create something useful! * Roman Cheplyaka: [51]V-Clip algorithm (status update). An update on Roman's Google Summer of Code project. * Andy Gill: [52]Memo class using type families. * >>> blueapple: [53]Project Euler. blueapple is hooked on [54]Project Euler and has been using it as an opportunity to learn Haskell. * >>> Dinesh Pillay: [55]Haskell & Type Inference. Dinesh has been learning Haskell for just a few days now and is really enjoying it. In this post he shares a problem he was having with types and its solution. * Don Stewart (dons): [56]Daily Haskell: Download and analyse logs, then generate sparklines. A new series on gluing Hackage libraries together to get things done. * Max Bolingbroke: [57]Compiler Plugins For GHC: Week Two. An update on Max's Google Summer of Code project. * Edward Kmett: [58]Paramorphism. * Edward Kmett: [59]Catamorphism. * Edward Kmett: [60]Recursion Schemes: A Field Guide. Edward is writing up a 'field guide' to all those 'foomorphism' recursion schemes. * Neil Mitchell: [61]GSoC Hoogle: Week 4. * Real World Haskell: [62]Ten new draft chapters. * Jamie Brandon: [63]Bitpacking. Updates on Jamie's Google Summer of Code project. * Jamie Brandon: [64]Finally!. * Brent Yorgey: [65]ZipEdit. Brent describes a new library for creating simple interactive list editors. * Real-World Haskell: [66]Video of my concurrent/multicore Haskell talk is up. * Roman Cheplyaka: [67]Status report: week 4. An update on Roman's Google Summer of Code project. * Osfameron: [68]More Countdown: laziness, Scheme, and German frogs. * Andrea Vezzosi (Saizan): [69]a dependency analysis framework for Cabal. * Osfameron: [70]Schwartzian transform in Haskell. * Neil Mitchell: [71]Hoogle 4 New Features. * Thomas M. DuBuisson: [72]Past and Future libraries. * >>> codeflow: [73]Haskell + a grain of Python. codeflow talks about his experience learning Haskell and functional programming. * >>> Peter Christensen: [74]Hey Language Snobs: Don't Pinch Pennies. * >>> Micah Elliott: [75]1983-96: The Golden Age of Programming Languages. Quotes of the Week * povman: when does ghc6.10 plan to release itself? * Baughn: So I just rewrote a fairly complex text extraction/indexing system to pipeline its work across several processors - painlessly, in less than five minutes. Bravo, haskell! * monochrom: We need to cabalise Cale. * Botje: h0t (monoid `mappend` monoid) action? * quicksilver: the only tool we have in haskell98 for performing an action is the magic sigil 'main =' * solrize: haskell has a very steep unlearning curve :) * Botje: drug users pass around needles, haskell users pass around Oleg papers * qwe1234: i know haskell, ocaml, scheme and prolog better than you ever will. About the Haskell Weekly News New editions are posted to [76]the Haskell mailing list as well as to [77]the Haskell Sequence and [78]Planet Haskell. [79]RSS is also available, and headlines appear on [80]haskell.org. Headlines are available as [81]PDF. To help create new editions of this newsletter, please see the information on [82]how to contribute. Send stories to byorgey at seas dot upenn dot edu. The darcs repository is available at darcs get [83]http://code.haskell.org/~byorgey/code/hwn/ . References 1. http://haskell.org/ 2. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41760 3. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044696.html 4. http://rippledeals.com:5001/ 5. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tutorial 6. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044671.html 7. http://biosimilarity.blogspot.com/2008/06/algebra-of-graphs-individually-an… 8. http://article.gmane.org/gmane.comp.lang.haskell.general/16263 9. https://www.softconf.com/s08/icfp08-posters/submit.html 10. http://www.haskell.org/pipermail/haskell-cafe/2008-June/044630.html 11. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/type-level 12. http://article.gmane.org/gmane.comp.lang.haskell.general/16260 13. http://socalfp.blogspot.com/ 14. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/ 15. http://www.realworldhaskell.org/blog/ 16. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/Pugs-6.2.13.2 17. http://pugscode.org/ 18. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41621 19. http://furius.ca/pubcode/pub/conf/common/bin/rst-literals.html 20. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41619 21. http://iki.fi/matti.niemenmaa/pipe/ 22. http://article.gmane.org/gmane.comp.lang.haskell.glasgow.user/14661 23. http://richardg.name/ 24. http://article.gmane.org/gmane.comp.lang.haskell.general/16252 25. http://code.google.com/p/hback/ 26. http://www.pnas.org/cgi/content/abstract/0801268105v1 27. http://www.haskell.org/gtk2hs/ 28. http://hackage.haskell.org/trac/summer-of-code/wiki/SoC2008 29. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html 30. http://www.haskell.org/haskellwiki/GHC/Data_Parallel_Haskell 31. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html 32. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html 33. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/ 34. http://www.haskell.org/haskellwiki/Template_Haskell 35. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.ht… 36. http://jamiiecb.blogspot.com/2008/06/gsoc-week-1.html 37. http://hackage.haskell.org/trac/ghc/wiki/GhcApiStatus 38. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41749 39. http://article.gmane.org/gmane.comp.lang.haskell.libraries/9334 40. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41651 41. http://thread.gmane.org/gmane.comp.lang.haskell.libraries/9259 42. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41607 43. http://www.haskell.org/ghc/docs/latest/html/libraries/base/Data-Foldable.ht… 44. http://thread.gmane.org/gmane.comp.lang.haskell.cafe/41506 45. http://www.cs.chalmers.se/~rjmh/Papers/pretty.ps 46. http://article.gmane.org/gmane.comp.lang.haskell.general/16253 47. http://article.gmane.org/gmane.comp.lang.haskell.cafe/41584 48. http://planet.haskell.org/ 49. http://haskell.org/haskellwiki/Blog_articles 50. http://idea-guy.blogspot.com/2008/06/converting-geosptial-coordinates.html 51. http://physics-dph.blogspot.com/2008/06/v-clip-algorithm-status-update.html 52. http://blog.unsafeperformio.com/?p=30 53. http://blueappledev.wordpress.com/2008/06/24/project-euler/ 54. http://projecteuler.net/ 55. http://dpillay.blogspot.com/2008/06/haskell-type-inference.html 56. http://www.cse.unsw.edu.au/~dons/blog/2008/06/24#daily-haskell-one 57. http://blog.omega-prime.co.uk/2008/06/23/compiler-plugins-for-ghc-week-two/ 58. http://comonad.com/reader/2008/paramorphism/ 59. http://comonad.com/reader/2008/catamorphism/ 60. http://comonad.com/reader/2008/recursion-schemes/ 61. http://neilmitchell.blogspot.com/2008/06/gsoc-hoogle-week-4.html 62. http://www.realworldhaskell.org/blog/2008/06/22/ten-new-draft-chapters/ 63. http://jamiiecb.blogspot.com/2008/06/bitpacking.html 64. http://jamiiecb.blogspot.com/2008/06/finally.html 65. http://byorgey.wordpress.com/2008/06/21/zipedit/ 66. http://www.realworldhaskell.org/blog/2008/06/20/video-of-my-concurrentmulti… 67. http://physics-dph.blogspot.com/2008/06/status-report-week-4.html 68. http://osfameron.vox.com/library/post/more-countdown-laziness-scheme-and-ge… 69. http://vezzosi.blogspot.com/2008/06/my-summer-of-code-project-dependency.ht… 70. http://osfameron.vox.com/library/post/schwartzian-transform-in-haskell.html… 71. http://neilmitchell.blogspot.com/2008/06/hoogle-4-new-features.html 72. http://tommd.wordpress.com/2008/06/18/past-and-future-libraries/ 73. http://codeflow.wordpress.com/2008/06/18/haskell-a-grain-of-python/ 74. http://www.pchristensen.com/blog/articles/hey-language-snobs-dont-pinch-pen… 75. http://micahelliott.blogspot.com/2008/06/1983-96-golden-age-of-programming.… 76. http://www.haskell.org/mailman/listinfo/haskell 77. http://sequence.complete.org/ 78. http://planet.haskell.org/ 79. http://sequence.complete.org/node/feed 80. http://haskell.org/ 81. http://code.haskell.org/~byorgey/code/hwn/archives/20080625.pdf 82. http://haskell.org/haskellwiki/HWN 83. http://code.haskell.org/~byorgey/code/hwn/

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Two questions regarding Alex/Parsec
by Niels Aan de Brugh 26 Jun '08

26 Jun '08

Hello Haskellers, As an experiment I'm writing a parser for MediaWiki language. I'm using the Alex lexer and Parsec. I have novice two questions. (I've tried using Happy but I was unable to get a grammar file to compile, which must be because I have no real experience using Yacc and the like. I've also attempted to write an ad-hoc recursive descent parser, but that become too complex to be fun very quickly.) == SourcePos and AlexPosn == My first question is about Parsec's SourcePos. I have a definition like: type LexToken = (AlexPosn, Token) type MWP a = GenParser LexToken () a toSourcePos :: AlexPosn -> SourcePos toSourcePos (AlexPn _ line col) = undefined mwtok :: (Token -> Maybe a) -> MWP a mwtok test = token showToken posToken posTest where showToken = show . snd posToken = toSourcePos . fst posTest = test . snd The definition of toSourcePos isn't 100% satisfactory. The constructor SourcePos is hidden, so I cannot simply use (SourcePos line col). Is there a way to convert an AlexPosn value to a SourcePos? == Data Constructors as Parameters and Tags == Secondly, I frequently encounter the pattern where I try to match a token, return Just some result if it matches, and Nothing otherwise. So I tried to fix this pattern in a nice reusable function. onTok0 :: Token -> a -> MWP a onTok0 t x = mwtok (\tok -> if tok `isTok` t then Just x else Nothing) This seems to work, but I'd also like a definition for data constructors taking one parameter: onTok1 :: (a -> Token) -> (a -> b) -> MWP b onTok1 t f = mwtok (\tok -> case tok of (t n) = Just $ f n _ = Nothing) This doesn't work, the pattern match (t n) fails, which is understandable: n is used as a parameter to t and a matched result, which looks like a paradox. t is a function (constructor) but also a tag. Is it possible to pass a tag as an argument? Or is there another way to extract this pattern? Regards, Niels

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Simple question about processing XML with HaXml
by Dominic Espinosa 25 Jun '08

25 Jun '08

Hello, I'm trying to learn how to use HaXml, but I'm having trouble getting off the ground. I can see from the documentation how to process XML using the combinators and processXmlWith, but processXmlWith seems to "hide" the actual process of reading and parsing the XML. Suppose that processXmlWith isn't suitable for a program. How then do you load the XML and apply filters to it? I guess what I'm asking is, given the following code: load filename = do handle <- IO.openFile filename IO.ReadMode contents <- IO.getContents handle IO.hclose handle return $ xmlParse filename contents myTest fname = do -- read file d <- load fname --- ?? now what? I'm sure the answer to this is quite simple, but I'm coming from a background of OO and SAX, and the HaXml docs are a bit cryptic as yet. Additionally, if anyone knows of any tutorials pertaining to HaXml, other than the papers on the HaXml website and the blog entries on cleaning legacy HTML, I'd appreciate some pointers. Thanks.

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ICFP08 Final Call for posters
by Matthew Fluet (ICFP Publicity Chair) 25 Jun '08

25 Jun '08

ICFP 2008 poster session September 21, 2008 Call for presentation proposals ICFP 2008 will feature a poster session for researchers and practitioners, including students. The session will provide friendly feedback for work that is in gestation or ongoing, as well as opportunities to meet each other and exchange ideas. We welcome poster submissions on all ICFP topics, especially presentations of - applications of and to functional programming; - recent work presented at more distant venues; and - ongoing work, whether or not submitted to ICFP. There will be no formal proceedings, but presenters will be invited to submit working notes, demo code, and other materials to supplement their abstract and poster. These materials will be released informally on a Web page dedicated to the poster session. An accepted submission is not intended to replace conference or journal publication. Persons interested in presenting a poster are invited to submit a one-page abstract in SIGPLAN conference style http://www.acm.org/sigs/sigplan/authorInformation.htm to the Web site https://www.softconf.com/s08/icfp08-posters/submit.html by June 30, 2008. The program committee will review the submissions for relevance and interest, and notify the authors by July 14, 2008. Accepted posters must be presented by the authors in person on Sunday, September 21, 2008. Important dates: Submission: Monday, June 30, 2008 Notification: Monday, July 14, 2008 Presentation: Sunday, September 21, 2008 Program committee: Benjamin Pierce (University of Pennsylvania) Colin Runciman (University of York) Chung-chieh Shan (Rutgers University)

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Help with generalizing function
by leledumbo 25 Jun '08

25 Jun '08

I've successfully create a function to return lists of N-ple that satisfy the following function: x1 + x2 + x3 + ... + xN = C But unfortunately, it's not generic. The N is supposed to be an input, too. I don't know how to make a dynamic N-ple (is it possible anyway?). Currently, here's the implementation: [code] findAllAns c = [ (x1,x2,x3,x4,x5) | x1 <- [0..c], x2 <- [0..c], x3 <- [0..c], x4 <- [0..c], x5 <- [0..c], x1 + x2 + x3 + x4 + x5 == c ] [/code] I tried using lists of lists, like this: [code] findAllAns c n = [ [x] | x <- [0..c], length [x] == n ] [/code] but [x] doesn't mean "a list of x", instead it's "a list that contains an x, where x in [0..c]". Can anyone help me? -- View this message in context: http://www.nabble.com/Help-with-generalizing-function-tp18063291p18063291.h… Sent from the Haskell - Haskell-Cafe mailing list archive at Nabble.com.

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Problem installing Cabal-1.4.0.1 with ghc-6.8.3
by Sasko Mateski 25 Jun '08

25 Jun '08

Hi, After reading the latest article on the Haskell Hacking blog (Daily Haskell: Download and analyse logs, then generate sparklines<http://cgi.cse.unsw.edu.au/%7Edons/blog/2008/06/24#daily-haskell-one>) I wanted to install cabal-install to check it out. Soon I found out that it has a dependency on Cabal (>=1.4&&<1.5), so next thing to do was getting and installing Cabal-1.4.0.1 (since the version coming with ghc-6.8.3 is 1.2.4.0). But during the configuration part of the installation I got the following error: During interactive linking, GHCi couldn't find the following symbol: SHGetFolderPathA@20 This may be due to you not asking GHCi to load extra object files, archives or DLLs needed by your current session. Restart GHCi, specifying the missing library using the -L/path/to/object/dir and -lmissinglibname flags, or simply by naming the relevant files on the GHCi command line. Alternatively, this link failure might indicate a bug in GHCi. If you suspect the latter, please send a bug report to: glasgow-haskell-bugs(a)haskell.org <glasgow-haskell-bugs(a)haskell.org> After some googling, I couldn't find anything on the web related to the problem, so posting to a Haskell mailing list seemed like an obvious next step. Since I'm a novice Haskell any help would be very much appreciated, indeed. I'm using *ghc-6.8.3* on a *Windows XP Professional SP3*. Regards *Sasko*

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Re: [Haskell-cafe] number-parameterized types and heterogeneous lists
by Harald ROTTER 25 Jun '08

25 Jun '08

Hello Anton, thanks for your enlightening piece of code. "foldD" does exactly what I was hoping for. Now it becomes very obvious to me that the positions of the forall's in the Digit definition are crucial. Thanks a lot to Alfonso, Luke and Ryan as well. Haskell Cafe is a really good place to learn new things :-) Harald. " Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite." " This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."

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Re: [Haskell-cafe] sdl-mixer loading issue
by Norbert Wojtowicz 25 Jun '08

25 Jun '08

> Attached is a patched version of SDL_mixer 0.5.2 with a C wrapper > for this macro. I'm now able to run loadWAV in ghci. Works for me, thanks! Now I just need to learn how to make my WAVs sound not like computer-generated children voices. For example, using the hback wav files and this: import Control.Concurrent (threadDelay) import Graphics.UI.SDL.Mixer.General import Graphics.UI.SDL.Mixer.Music main = do openAudio 22050 AudioS16Sys 2 4096 w <- loadMUS "c.wav" playMusic w 1 threadDelay 2000000 freeMusic w closeAudio It plays (which is an immense improvement), but I can't get it to sound the way it does from eg. mplayer. I have almost no knowledge of the inner workings of computer sound drivers, so if there is something obvious I'm missing please do speak up. - Norbert

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Why the exception?
by Thomas M. DuBuisson 25 Jun '08

25 Jun '08

Cafe I'm a bit lost on this exception and curious about what's going on. Is there a valid reason for this exception that I am missing? Note the hard-coded [0..100] could be any Word8 list you want (generated via arbitrary, [], or other) and it gives the same result. Load the module and perform: :break prop_LPS quickCheck prop_LPS :step :force ps *** Exception: Prelude.head: empty list > import qualified Data.ByteString as L > import Test.QuickCheck > > instance Arbitrary L.ByteString where > arbitrary = do > return $ L.pack [0..100] > > prop_LPS :: L.ByteString -> Bool > prop_LPS ps = ps `seq` True P.S. Same result with GHCi 6.8.2 and 6.8.3.

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Fwd: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
by tphyahoo 25 Jun '08

25 Jun '08

---------- Forwarded message ---------- From: tphyahoo <thomashartm...@googlemail.com> Date: Jun 24, 7:46 pm Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial To: HAppS There are some issues with the cabalized project -- templates are missing. Doh. Use darcs for now. Thomas. On Jun 24, 7:26 pm, tphyahoo <thomashartm...@googlemail.com> wrote: > Hello HAppSers! > I have created a self-demoing, HStringTemplate-using intro to HAppS. > There is a live demo at >http://rippledeals.com:5001 > It is cabalized at >http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto... > and should install fine with sudo cabal install happs-tutorial. > There is a darcs repo at >http://code.haskell.org/happs-examples > And a google project at >http://code.google.com/p/happs-tutorial/ > which currently isn't used, but who knows, maybe for the wiki or issue > tracking. (I started at google hosting before migrating to darcs.) > I have all kinds of additional lessons planned, but under the release > early/release often motto I'm letting it out in its embryonic state. > Enjoy! > Thomas.

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Fwd: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial
by tphyahoo 25 Jun '08

25 Jun '08

---------- Forwarded message ---------- From: tphyahoo <thomashartm...@googlemail.com> Date: Jun 24, 7:26 pm Subject: Cabalized, Self-Demoing, HStringTemplate-using HAppS Tutorial To: HAppS Hello HAppSers! I have created a self-demoing, HStringTemplate-using intro to HAppS. There is a live demo at http://rippledeals.com:5001 It is cabalized at http://hackage.haskell.org/cgi-bin/hackage-scripts/package/happs-tuto... and should install fine with sudo cabal install happs-tutorial. There is a darcs repo at http://code.haskell.org/happs-examples And a google project at http://code.google.com/p/happs-tutorial/ which currently isn't used, but who knows, maybe for the wiki or issue tracking. (I started at google hosting before migrating to darcs.) I have all kinds of additional lessons planned, but under the release early/release often motto I'm letting it out in its embryonic state. Enjoy! Thomas.

1 0

Bug in Emacs Haskell Mode
by Ronald Guida 25 Jun '08

25 Jun '08

Emacs Haskell Mode has the following useful feature: when "Haskell -> Load File" is used to load a file into GHCi from Emacs, Haskell Mode automatically looks for a "*.cabal" file in an attempt to find the project directory. When Haskell Mode finds the *.cabal file, it fails to check whether it has found a file or a folder. As a result, if I want to load a Haskell file that has no corresponding .cabal file, then Haskell Mode locates my "~/.cabal" *folder* and assumes that it's my project directory. I have a "~/.cabal" folder because Cabal-Install puts it there. Cabal-Install is part of Haskell's new package management system. Now I don't know very much Emacs Lisp, but I figured out a fix for the problem. In Haskell-Mode-2.4, in the file haskell-cabal.el, I changed the function "haskell-cabal-find-file" so that it explicitly checks to make sure that any *.cabal file is in fact a file and not a folder. I don't know if comparing the first letter of the file mode string to 'd' is the right way to diferentiate a folder from a file, but so far it appears to work for me, so I thought I'd share it. (defun haskell-cabal-find-file () "Return a buffer visiting the cabal file of the current directory, or nil." (catch 'found (let ((user (nth 2 (file-attributes default-directory))) ;; Abbreviate, so as to stop when we cross ~/. (root (abbreviate-file-name default-directory)) files) (while (and root (equal user (nth 2 (file-attributes root)))) (let ((files (directory-files root 'full "\\.cabal\\'"))) (if (and files (not (equal 100 (aref (nth 8 (file-attributes (car files))) 0)))) (throw 'found (find-file-noselect (car files))) (if (equal root (setq root (file-name-directory (directory-file-name root)))) (setq root nil)))) nil))))

2 1

sdl-mixer loading issue
by Norbert Wojtowicz 25 Jun '08

25 Jun '08

Hello, I am trying to use the SDL-mixer bindings to play wav files. I've hit a wierd error and I can't figure out how to solve it: Prelude> import Graphics.UI.SDL.Mixer.Music Prelude Graphics.UI.SDL.Mixer.Music> loadMUS "test.wav" Loading package SDL-0.5.4 ... linking ... done. Loading package SDL-mixer-0.5.2 ... linking ... <interactive>: /home/norbert/bin/lib/SDL-mixer-0.5.2/ghc-6.8.2/HSSDL-mixer-0.5.2.o: unknown symbol `Mix_LoadWAV' ghc-6.8.2: unable to load package `SDL-mixer-0.5.2' I've looked up the source code; Mix_LoadWAV seems to be #defined, so I suspect it's some kind of library path issue but I don't grok the whole system well enough to figure it out; maybe someone could point me in the right direction? Have the issue now on Ubuntu 8.04 and previously had the same issue when I tested it on a FreeBSD box. I did install all of the "libsdl-*-dev" in the Ubuntu repo. - Norbert

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Template Haskell ListT wrinkle
by Robert Greayer 25 Jun '08

25 Jun '08

In messing around with TH, I noticed (what I consider to be an) odd wrinkle in the handling of list types within TH's syntax meta-data. For example, given the program at the end of this email, which prints out the TH representation of the types 'Ints' and '[Int]', where 'Ints' is just a type-alias for '[Int]', the following results are generated: Ints is: AppT (ConT GHC.Base.[]) (ConT GHC.Base.Int) [Int] is: AppT ListT (ConT GHC.Base.Int) type0, 'Ints' resolves to the application of the named type constructor "GHC.Base.[]" to the named type constructor "GHC.Base.Int" (which makes perfect sense). type1, '[Int]' resolves to the application of the 'built-in' ListT type constructor to the named type constructor "GHC.Base.Int" (which also makes perfect sense). What's odd (to me) is that in one situation, the 'named' constructor 'GHC.Base.[]' appears, and in the other, the 'built-in' constructor appears. Does anyone have insight into why this might be? (These results were obtained with GHC 6.8.2, btw). > {-# OPTIONS_GHC -XTemplateHaskell #-} > module Main where > import Language.Haskell.TH > > type Ints = [Int] > > type0 = $( reify ''Ints >>= (\ (TyConI (TySynD _ _ t)) -> return $ show t) >>= \s -> [| s |]) > type1 = $( [t| [Int] |] >>= return . show >>= \s -> [| s |]) > > main = do > putStrLn ("Ints is: " ++ type0) > putStrLn ("[Int] is: " ++ type1) Thanks rcg

2 1

safe vs unsafe
by Galchin, Vasili 25 Jun '08

25 Jun '08

Hello, At runtime, I am getting .... aio: schedule: re-entered unsafely. Perhaps a 'foreign import unsafe' should be 'safe'? I want to understand from an implementation viewpoint .. deeper. This is a GC issue yes? Kind regards, Vasili

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Re: number-parameterized types and heterogeneous lists
by oleg＠okmij.org 24 Jun '08

24 Jun '08

Luke Palmer wrote in response to Harald ROTTER > > I also wonder if there is some kind of "generalized" foldr such that, e.g. > > D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0] > > I think that this foldr must be some "special" foldr that augments the data > > type of the result in each foldr step. > > Would this be possible or am I just chasing phantoms ? > Mostly I believe you are. What you are describing is firmly in the > realm of dependent types, far beyond Haskell's type system. See > Epigram or Agda for languages which have attempted to tackle this > problem. First of all, Haskell (as implemented by released versions of GHC for at least two years) already permits dependent types, in the strict sense of a type of an expression being determined by the value of one argument of that expression: http://okmij.org/ftp/Computation/tagless-typed.html#tc-GADT-tc Second, (values of) types like D0 and D1 can be collected in a heterogenous list (HList), which does have the corresponding fold operator, called HFoldr in http://darcs.haskell.org/HList/Data/HList/HListPrelude.hs

1 0

"C" buffer suggestions??
by Galchin, Vasili 24 Jun '08

24 Jun '08

Hello, I want to model an I/O read/write buffer in Haskell and marshall down into ANSI C. 1) ByteString? Or Ptr Word8? 2) What are example values of the types in 1)? Kind regards, Vasili

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Re: [Haskell-cafe] number-parameterized types and heterogeneous lists
by Harald ROTTER 24 Jun '08

24 Jun '08

Hello, sorry for the late answer, I was off for the weekend :-) The paper "Number-parameterized types" by Oleg Kielyov is located at http://okmij.org/ftp/papers/number-parameterized-types.pdf It impressively shows what one can do with Haskell's type system. What I am after is the replacement of a "chain" of digits, like e.g. D1 $ D0 $ D0 $ Sz by a list [D1,D0,D0] so I can effectively use list operations on those "typed numbers". I also wonder if there is some kind of "generalized" foldr such that, e.g. D1 $ D0 $ D0 $ Sz = specialFoldr ($) Sz [D1,D0,D0] I think that this foldr must be some "special" foldr that augments the data type of the result in each foldr step. Would this be possible or am I just chasing phantoms ? Thanks Harald. " Ce courriel et les documents qui y sont attaches peuvent contenir des informations confidentielles. Si vous n'etes pas le destinataire escompte, merci d'en informer l'expediteur immediatement et de detruire ce courriel ainsi que tous les documents attaches de votre systeme informatique. Toute divulgation, distribution ou copie du present courriel et des documents attaches sans autorisation prealable de son emetteur est interdite." " This e-mail and any attached documents may contain confidential or proprietary information. If you are not the intended recipient, please advise the sender immediately and delete this e-mail and all attached documents from your computer system. Any unauthorised disclosure, distribution or copying hereof is prohibited."

3 2