Re: [Haskell-cafe] Re: cabal install HaXml installs wrong version unless I specify the version number
Don Stewart wrote: [...] Note that packages that depend on the 'experimental' versions of things (in particular Haxml 1.19.* can't be packaged for Arch either, as we can only install one version of the haskell-haxml package). In this case we definetely need haxml-1.19. IIRC we even committed patches to the haxml repository, when we were developing Barracuda a year ago :) //Stephan -- Früher hieß es ja: Ich denke, also bin ich. Heute weiß man: Es geht auch so. - Dieter Nuhr ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] HAPPS on a major hosting provider?
I was wondering if anyone's ever tried to run Haaps on a major hosting provider, like oh, say Site5? I have an app I'd otherwise use Rails for and I thought I'd give Haaps a try... -- Jeff I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Find unused exports
On Sun, Nov 16, 2008 at 5:35 AM, Thomas Schilling [EMAIL PROTECTED] wrote: The relevant flag is: -ddump-minimal-imports See http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html#id2630684 The documentation says this: -ddump-minimal-imports Dump to the file M.imports (where M is the module being compiled) a minimal set of import declarations. You can safely replace all the import declarations in M.hs with those found in M.imports. Why would you want to do that? Because the minimal imports (a) import everything explicitly, by name, and (b) import nothing that is not required. It can be quite painful to maintain this property by hand, so this flag is intended to reduce the labour. I already know the minimal set of import for the modules. That's why I mentioned using -Wall; ghc will complain if you import something and don't use it. The problem is that you can export names that never get used in other modules. I would like a tool that can look over a project and tell me which exported names are never imported. These names correspond to things that can be removed from the project. Thanks, Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Type question in instance of a class
Hi, Why is this wrong? class MyClass r where function :: r - s data MyData u = MyData u instance MyClass (MyData v) where function (MyData a) = a GHC says that the type of the result of 'function' is both determined by the rigid type from MyClass and the rigid type from MyData. But why can't both be the same? What am I doing wrong? Thanks for your help, Maurício ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type question in instance of a class
Hello Maurício, Monday, November 17, 2008, 12:32:11 AM, you wrote: class MyClass r where function :: r - s this tells that f may return value of any type requested at the call site, i.e. one can write main = do print (f (Mydata 1) :: String) print (f (Mydata 1) :: [Bool]) print (f (Mydata 1) :: Either Double Float) instance MyClass (MyData v) where function (MyData a) = a this definition can return value of only one type, so it can't serve all the calls i mentioned above GHC says that the type of the result of 'function' is both determined by the rigid type from MyClass and the rigid type from MyData. But why can't both be the same? are you OOPer? :) ps: GHC error messages should be fired :) -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type question in instance of a class
On Sun, Nov 16, 2008 at 1:32 PM, Maurício [EMAIL PROTECTED] wrote: Hi, Why is this wrong? class MyClass r where function :: r - s data MyData u = MyData u instance MyClass (MyData v) where function (MyData a) = a GHC says that the type of the result of 'function' is both determined by the rigid type from MyClass and the rigid type from MyData. But why can't both be the same? As Bulat said, your type signature is equivalent to: function :: forall r s. r - s whereas the result you're producing can't produce any s, but only particular s's. In essence, the result type is determined by the input type. One way to code this would be to use functional dependencies: class MyClass r s | r - s where function :: r - s data MyData u = MyData u instance MyClass (MyData v) v where function (MyData a) = a /g -- I am in here ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type question in instance of a class
Maurício wrote:
Hi,
Why is this wrong?
class MyClass r where function :: r - s
data MyData u = MyData u
instance MyClass (MyData v) where function (MyData a) = a
GHC says that the type of the result of 'function' is both determined by
the rigid type from MyClass and the rigid type from MyData. But why
can't both be the same?
particular instances can't add extra restrictions (eg: both types are
the same) to the interface declared by the class (eg: both types are
arbitrary).
Compare this version:
8
{-# LANGUAGE MultiParamTypeClasses, FlexibleInstances #-}
module Test where
class MyClass r s where function :: r - s
data MyData u = MyData u
instance MyClass (MyData v) v where function (MyData a) = a
8
And ghci session:
8
*Test function (MyData hello)
interactive:1:0:
No instance for (MyClass (MyData [Char]) s)
arising from a use of `function' at interactive:1:0-24
Possible fix:
add an instance declaration for (MyClass (MyData [Char]) s)
In the expression: function (MyData hello)
In the definition of `it': it = function (MyData hello)
*Test :t function (MyData hello)
function (MyData hello) :: (MyClass (MyData [Char]) s) = s
*Test function (MyData hello) :: String
hello
8
I don't know how evil those language extensions are, though - I just
fiddled until it worked...
What am I doing wrong?
Claude
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http://claudiusmaximus.goto10.org/
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Re[2]: [Haskell-cafe] Type question in instance of a class
Hello J., Monday, November 17, 2008, 12:56:02 AM, you wrote: class MyClass r where function :: r - s As Bulat said, your type signature is equivalent to: function :: forall r s. r - s only function :: forall s. r - s (r is fixed in class header) -- Best regards, Bulatmailto:[EMAIL PROTECTED] ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Type question in instance of a class
On Sun, Nov 16, 2008 at 2:01 PM, Claude Heiland-Allen [EMAIL PROTECTED] wrote: I don't know how evil those language extensions are, though - I just fiddled until it worked... The only part of FlexibleInstances that you've used here is the ability to mention a type variable more than once in the instance. I really wish this came with MultiParamTypeClasses. My reasoning is this, FlexibleInstances turns on a lot of extra stuff, as do functional dependencies. And yet, once you have multiparam type classes one of the natural things you want is the ability to mention a type variable more than once but currently you have to enable a lot of extra baggage to get that ability. I'm not an expert, the way you've used them together seems quite sane and by using those extensions instead of some of the more powerful ones you've probably done yourself a favor :) Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] HAPPS on a major hosting provider?
Hello, I have run HAppS applications on VPSs from vpslink.com and rimuhosting.com. If you want shared hosting, then you would need to get FastCGI support working again (I assume it has bitrotted somewhat). Because of HAppS's preference for storing everything in RAM, it is not really a shared-host friendly architecture. A $14.95/month 128MB VPS from vpslink seems to work fine as a entry-level solution though. - jeremy At Sun, 16 Nov 2008 14:04:51 -0500, Jefferson Heard wrote: I was wondering if anyone's ever tried to run Haaps on a major hosting provider, like oh, say Site5? I have an app I'd otherwise use Rails for and I thought I'd give Haaps a try... -- Jeff I try to take things like a crow; war and chaos don't always ruin a picnic, they just mean you have to be careful what you swallow. -- Jessica Edwards ___ 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: Type question in instance of a class
Bulat Ziganshin wrote: Hello J., Monday, November 17, 2008, 12:56:02 AM, you wrote: class MyClass r where function :: r - s As Bulat said, your type signature is equivalent to: function :: forall r s. r - s only function :: forall s. r - s (r is fixed in class header) ... and the only value the function can return is bottom. Is there any type system which would have more than one value which inhabits all types? Peter. ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Type question in instance of a class
On Sun, Nov 16, 2008 at 5:06 PM, Peter Hercek [EMAIL PROTECTED] wrote: ... and the only value the function can return is bottom. Is there any type system which would have more than one value which inhabits all types? Well something like lazy C# might; i.e. every value has a _|_ (nontermination) and null (termination but undefined). Luke ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Re: Type question in instance of a class
On Sun, Nov 16, 2008 at 7:09 PM, Luke Palmer [EMAIL PROTECTED] wrote: On Sun, Nov 16, 2008 at 5:06 PM, Peter Hercek [EMAIL PROTECTED] wrote: ... and the only value the function can return is bottom. Is there any type system which would have more than one value which inhabits all types? Well something like lazy C# might; i.e. every value has a _|_ (nontermination) and null (termination but undefined). For that matter, Control.Exception allows you to distinguish exceptional values from each other. -- Dave Menendez [EMAIL PROTECTED] http://www.eyrie.org/~zednenem/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Re: Haskell Weekly News: Issue 93 - November 15, 2008
Brent Yorgey wrote: --- ANN: OpenGL with extra type safety. Neal Alexander Hopefully the code will be uploaded to Hackage as a separate package soon. http://hackage.haskell.org/cgi-bin/hackage-scripts/package/OGL-0.0.0 http://haskell.org/haskellwiki/OGL ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Find unused exports
Within a set of modules, the minimal imports also give you the minimal exports since each minimal export is required because it is imported somewhere. Just compile all your modules with -ddump-minimal-imports, then cat all your *.import files together and sort the result. The minimal exports for module Foo will be listed as several lines of the form import Foo(x,y,z), etc. From there on it's just a bit of text munging to get it into your export list code (about two lines of perl). Michael D. Adams 2008/11/16 Jason Dagit [EMAIL PROTECTED]: On Sun, Nov 16, 2008 at 5:35 AM, Thomas Schilling [EMAIL PROTECTED] wrote: The relevant flag is: -ddump-minimal-imports See http://www.haskell.org/ghc/docs/latest/html/users_guide/flag-reference.html#id2630684 The documentation says this: -ddump-minimal-imports Dump to the file M.imports (where M is the module being compiled) a minimal set of import declarations. You can safely replace all the import declarations in M.hs with those found in M.imports. Why would you want to do that? Because the minimal imports (a) import everything explicitly, by name, and (b) import nothing that is not required. It can be quite painful to maintain this property by hand, so this flag is intended to reduce the labour. I already know the minimal set of import for the modules. That's why I mentioned using -Wall; ghc will complain if you import something and don't use it. The problem is that you can export names that never get used in other modules. I would like a tool that can look over a project and tell me which exported names are never imported. These names correspond to things that can be removed from the project. Thanks, Jason ___ 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] Find unused exports
On Sun, Nov 16, 2008 at 5:10 PM, Michael D. Adams [EMAIL PROTECTED]wrote: Within a set of modules, the minimal imports also give you the minimal exports since each minimal export is required because it is imported somewhere. Just compile all your modules with -ddump-minimal-imports, then cat all your *.import files together and sort the result. The minimal exports for module Foo will be listed as several lines of the form import Foo(x,y,z), etc. From there on it's just a bit of text munging to get it into your export list code (about two lines of perl). Alright, that's the same manual process I do now. I didn't use -ddump-minimal-imports before because I didn't know about it and we maintain sufficiently minimal imports already. That and I used emacs macros instead of perl because I already know how to use emacs :) If I take the time to automate this I wonder if it's a worthwhile tool to upload to hackage. Sounds like others have been doing this sort of thing. Now if I just had a round touit... Thanks everyone! Jason ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
