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Re: [Haskell-cafe] Re: Strings - why [Char] is not nice
by MR K P SCHUPKE 28 Sep '04

28 Sep '04

Can this not be handled in a nicer way by the compiler? What if the compiler tried to allocate the lists in chunks? For example when dealing with strings, why cant the compiler allocate the string as a fixed length unit, terminated with a link to the next unit. (IE allow the atoms in the list to be variable size). In this way functions which return blocks of data (for example reading a file in 8k buffers) can be treated just like reading a normal list. This would not only save memory, but would make IO more efficient, whilst retaining a Haskell-like style of coding. Keean.

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Re: [Haskell-cafe] mutually recursive modules
by Henning Thielemann 28 Sep '04

28 Sep '04

On Fri, 24 Sep 2004, Malcolm Wallace wrote: > Hugs doesn't support mutually-recursive modules at all. Ghc and nhc98 > support them only if you hand-write a .hi-boot file to bootstrap the > compilation. I would guess that better support from the mainstream > implementations is unlikely, because it would be a large amount of > effort for a situation which occurs only very rarely, and for which > there is a relatively easy workaround. Namely? The only workaround I know of is putting all type declarations and functions that depend on each other into one module, import them in the modules they logically belong to and document that the objects should be imported from the redirecting modules rather than from the modules they are defined in. I know of two projects where different tasks had to be merged into one module because of the lack of mutually recursive imports, namely functionalMetaPost and Haskore. It's interesting how other languages solve this problem. In Modula-3 it is solved by explicit module interfaces and partial revelation. One can define type T in module A and type T in module B very abstractly as pointers to something and the complete data structures (which may contain references to either interface) are usually revealed in the implementations of the modules. I'm curious how Oberon solves it, because it doesn't need explicit interfaces but derives them from the implementation files. Probably one can say that Oberon extracts something like a .hiboot file from every module file automatically. Why can't GHC and Hugs go this way?

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job ads I saw on DICE
by Christopher Milton 25 Sep '04

25 Sep '04

It is rare to see ads looking for Haskell programming experience... http://seeker.dice.com/jobsearch/servlet/JobSearch?op=1002&dockey=xml/6/2/6… http://seeker.dice.com/jobsearch/servlet/JobSearch?op=1002&dockey=xml/b/8/b…

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Re: [Haskell-cafe] mutually recursive modules
by Malcolm Wallace 24 Sep '04

24 Sep '04

Henning Thielemann <iakd0(a)clusterf.urz.uni-halle.de> writes: > As far as can see neither Hugs or GHC really support them. Is this still > on the to-do list or is it almost dropped due to implementation > difficulties? Hugs doesn't support mutually-recursive modules at all. Ghc and nhc98 support them only if you hand-write a .hi-boot file to bootstrap the compilation. I would guess that better support from the mainstream implementations is unlikely, because it would be a large amount of effort for a situation which occurs only very rarely, and for which there is a relatively easy workaround. Some lesser-known Haskell implementations do fully support mutually-recursive modules however. hhc (formerly Freja, from Henrik Nilsson) allows multiple modules to be stored in a single file, and hence mutual recursion can be achieved by ensuring all the recursive modules are compiled simultaneously from the same file. The PacSoft Haskell system (from the Programatica project at OGI) also fully supports mutually recursive modules, and I believe they can even be in separate files. Regards, Malcolm

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mutually recursive modules
by Henning Thielemann 24 Sep '04

24 Sep '04

As far as can see neither Hugs or GHC really support them. Is this still on the to-do list or is it almost dropped due to implementation difficulties?

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Job
by Mark Carroll 24 Sep '04

24 Sep '04

The company I'm involved with - Aetion, a tiny defense contractor in Columbus, Ohio - is now looking for an affordable Haskell programmer to hire. So, on the offchance that any of you guys are interested, or know of someone who might be, feel free to e-mail me for more information or to supply your resume. Unfortunately, the nature of the work is such that US citizenship or a security clearance would help, and telecommuting isn't really an option. On the upside, the work should be varied and interesting - more challenging than mundane. Given that fact, we are more interested in aptitude than specific experience. -- Mark

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The implementation of functional languages
by mattr 21 Sep '04

21 Sep '04

I am working thru "Implementing Functional Languages: a tutorial" and I want to look up one of the references to get more details. I am looking for the book "The implementation of Functional Programming languages" by S. L. Peyton Jones. Anyone know how I can get it? I would be willing to pay for a second hand copy if anyone has one. Matt

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no dynamic binding
by Andrew Harris 21 Sep '04

21 Sep '04

Hi - I have another question. I am still working on a soccer server and thought it would be neat to create command objects that had a "toString" method. Then, I was going to keep a list of these command objects and at the right time stringify them and send them to the server. So I created a class with a toString method: class ServerCommandClass a where toString :: a -> String And then a few instances: -- dash command data DashCommand = DashCommand { dashpower :: Double } instance ServerCommandClass DashCommand where toString c = "(dash " ++ show (dashpower c) ++ ")\n" -- move command data MoveCommand = MoveCommand { x :: Double, y :: Double } instance ServerCommandClass MoveCommand where toString c = "(move " ++ show (x c) ++ " " ++ show (y c) ++ ")\n" The problem is, I am not quite sure how to describe a *list* of command objects where the list could have both DashCommands and MoveCommands in it. Ideally the list could contain both, and then for each item in the list I could call the toString method. I was reading Simon Thompson's Haskell: The Craft of Functional Programming and I read that Haskell 98 does not support dynamic binding, which (it seems) is what I'm trying to do. Does anyone have a suggestion on an alternative approach? thanks, -andrew

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Re: [Haskell-cafe] Strings - why [Char] is not nice
by MR K P SCHUPKE 20 Sep '04

20 Sep '04

Would it not bet better is String were a typeclass instead of a data type. Then the string operations could be redefined by implementation, so you may have strings as lists or strings as arrays? Keean.

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Re: [Haskell-cafe] no dynamic binding
by Abraham Egnor 20 Sep '04

20 Sep '04

You can use exisential types to do what you'd like. From memory, so there are probably errors: newtype ServerCommand = forall a. ServerCommandClass a => ServerCommand a instance ServerCommandClass ServerCommand where toString (ServerCommand c) = toString c commands :: [ServerCommand] commands = [ServerCommand $ DashCommand ..., ServerCommand $ MoveCommand ...] Also, for a less type-safe approach, see Data.Dynamic. On Sun, 19 Sep 2004 13:48:53 -0400, Andrew Harris <andrew.unit(a)gmail.com> wrote: > Hi - > > I have another question. I am still working on a soccer server and > thought it would be neat to create command objects that had a > "toString" method. Then, I was going to keep a list of these command > objects and at the right time stringify them and send them to the > server. So I created a class with a toString method: > > class ServerCommandClass a where > toString :: a -> String > > And then a few instances: > > -- dash command > data DashCommand = > DashCommand { dashpower :: Double } > > instance ServerCommandClass DashCommand where > toString c = "(dash " ++ show (dashpower c) ++ ")\n" > > -- move command > data MoveCommand = > MoveCommand { x :: Double, > y :: Double } > > instance ServerCommandClass MoveCommand where > toString c = "(move " ++ show (x c) ++ " " ++ show (y c) ++ ")\n" > > The problem is, I am not quite sure how to describe a *list* of > command objects where the list could have both DashCommands and > MoveCommands in it. Ideally the list could contain both, and then for > each item in the list I could call the toString method. > > I was reading Simon Thompson's Haskell: The Craft of Functional > Programming and I read that Haskell 98 does not support dynamic > binding, which (it seems) is what I'm trying to do. Does anyone have > a suggestion on an alternative approach? > > thanks, > -andrew > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe >

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