- Haskell - Haskell.org

Follow up question
by MikeKn22＠aol.com 03 Apr '01

03 Apr '01

I am a bit confused by your response Mieszko. What I am looking to do is have a function say called ConvertString :: IO String -> String or something like that. Not sure if your examples achieve this. I want to take the IO String and be able to use it as a String somehow. My problem is I have a function for instance getWord :: String -> String getWord [] = [] getWord (x:xs) | elem x whitespace = [] | otherwise = x : getWord xs If I change the header to getWord :: IO String -> IO String I get errors of types not matching. Sorry if these are stupid questions but I am very confused by the difference of IO String and String, and want to know how you can use the IO String like a String. Thank you. Rob

3 2

Hello List Have an IO String question
by MikeKn22＠aol.com 02 Apr '01

02 Apr '01

I am new to the list and to Haskell, and would appreciate any help anyone can give me on a problem I am having. I am using Hugs98 in case that matters. My question involved reading from a file. I used the line: readFile "c:/myfile.txt" To read my file and this works fine. I now want to take the contents of the file and use it in a function that takes in a String, but am getting an error since readFile returns an IO String. Is there a way to convert an IO String to a normal String? Thank you all. Rob

2 1

Multiple modules in a file
by andrew＠andrewcooke.free-online.co.uk 02 Apr '01

02 Apr '01

Hi, I don't seem to be able have multiple modules in one file (at least for hugs and ghc). The gentle intro says that there is no restriction and I can't find any mention in the ghc jobs (apart from a recommendation to name a file after the module it contains to help make). It's not a desperate problem - I can split files - but I'd like to know if I'm doing something stupid, or if this is a real restriction. (I can see arguments why from an engineering/maintenance point of view, but one module is small and fits nicely with another; it also makes literate programming slightly more complicated). Thanks, Andrew -- http://www.andrewcooke.free-online.co.uk/index.html

2 1

question class tree
by Maldonado Castiblanco Camilo Ernesto 02 Apr '01

02 Apr '01

I need a class tree for haskell. where can i find it?

2 1

ffi & recursive data types
by dario.bahena＠correo.unam.mx 02 Apr '01

02 Apr '01

hi ... I'm new in ffi stuff and tools like greencard. Everything was working ok, until I wanted to: translate a haskell recursive data type(list,trees,etc) into a corresponding C type and back again. How can I do this? Thanks in advance saludos dario estepario ... ------------------------------------------------- Obtén tu correo en www.correo.unam.mx UNAMonos Comunicándonos

2 1

modules Eigensystem and LinearAlgorithms
by Jan Skibinski 02 Apr '01

02 Apr '01

Experimenting recently with some quantum problems I've decided that it's time to add some long overdue algorithmic support for module QuantumVector. So here are two new modules added to our collection: http://www.numeric-quest.com/haskell/LinearAlgorithms.hs http://www.numeric-quest.com/haskell/Eigensystem.hs The former partially overlaps with module Orthogonals, but their most important algorithms are different, although both modules use lists for representation of matrices. This is still work in progress, but usable as it is for Hermitian matrices. Both modules are thoroughly documented, so here are just few buzzwords: Housholder reduction, complex reflection, Hessenberg matrix, similarity, triangularization, tridiagonalization, operators and maps. Jan

1 0

[Fwd: beginners silly question : apologies and lib question]
by luc 01 Apr '01

01 Apr '01

1 0

Re: Welcome to the "Haskell" mailing list
by luc 31 Mar '01

31 Mar '01

haskell-request(a)haskell.org wrote: > Welcome to the Haskell(a)haskell.org mailing list! > > To post to this list, send your email to: > > c > hi. im just a newcomer to haskell (www.taesch.com) quite impressed till now ! im trying to have haxml lib running with hugs and had the following problem : 1) under win, quite an issue to tun the cpp stuff. did it under linux, (for info) 2) then i had a "maybeA" which is unknown. some lib i had to add ? ("maybe" doesnt seems to work) 3) a module declare a "with" function, which hugs doenst seem to like . renamed it withlt for now. this make me thinks that this lib is probably not tested under hugs98. could someone confirm that ? as im too newbies, im maybe missing something obvious. Id better asking, i thought. thanks Luc

3 2

A GUI toolkit looking for a friend
by Simon Peyton-Jones 31 Mar '01

31 Mar '01

Gentle Haskellers This message is to invite offers to complete a promising port of the Clean Object I/O library to Haskell. As you know, there are quite a few GUI toolkits for Haskell, but none of them has become a de-facto standard. One confusing aspect is that there are different "levels": (see http://haskell.org/libraries/#guigs) * Low-level veneers on top of existing libraries. HOpenGL, GTK, TclHaskell, the Win32 library, all fall into this category. They are rich, but hard to use because you have to adopt the programming model of the library, which is usually very imperative. * Very high-level systems, such as Fudgets, Haggis, FranTk. These are rather sophisticated and (esp Fudgets, FranTk) attempt to break with the imperative programming model. But I don't think any of them has been acclaimed as The Right Way To Do It. We're still looking! * Strangely, there are very few "in the middle" systems. One might hope for an interface that was somewhat independent of the low-level library, and somewhat more Haskell friendly, than the low-level veneers, but not as ambitious as the high-level systems. On top of that, some libraries deal in graphical user interfaces (buttons, menus..) and some deal in graphics (pictures, lines, shading). I think we should encourage the development of more "in the middle" systems. One example is Koen Claessen's Yahu system, http://www.cs.chalmers.se/Cs/Grundutb/Kurser/afp/yahu.html However, there is another functional language that has put years of development into a GUI library: Clean. The Clean Object I/O library is well-documented and the Clean team have had a lot of experience in using it. It runs on both Windows and Mac, but not currently on Unix. http://www.cs.kun.nl/~clean/About_Clean/page_modified/page_modified.html Maybe we should build on their experience! Peter Achten, its author, spent a few weeks in Cambridge, porting the Clean library to Haskell. The results are very promising. The main ideas come over fine, translating unique-types to IO monad actions, and the type structure gets a bit simpler. So what we need now is to complete the port. Peter didn't have time to bring over all the widgets, nor did he have time to clean up the Haskell/C interface. (Clean's FFI is not as well-developed as Haskell's, so the interface can be made much nicer.) The other significant piece of work would be to make it work on Unix, perhaps by re-mapping it to GTK or TkHaskell or something. So the main burden of this message is: Would anyone be interested in completing the port? Fame (if not fortune) await you! The prototype that Peter developed in is the hslibs/ CVS repository, and the GHC team would be happy to work with you to support your work. (The more compiler-independent we can make the library, the better.) Peter Achten is willing to play consultant too. The Clean team are happy for the code to be open source -- indeed, all the hslibs/ code is BSD-licensed. It would not be the work of a moment. There are subtle issues involved (especially involving concurrency), and the design is not complete, so it isn't just boring hacking. So it should fun. Anyone interested? Maybe more than one person could work on it together. [And are there any other "in-the-middle" libraries I've overlooked?] Simon

3 2

RE: FixIO/ Tackling Awkward Squad
by Simon Peyton-Jones 31 Mar '01

31 Mar '01

| Dear Haskellers, | After enjoying "Tackling the Awkward Squad" (Simon | Peyton Jones), I wonder what other elements of the | squad can be tackled in a simular way? Right now I am | thinking about FixIO. This little bugger seems to show | up in a lot of code! Can we give it an operational | semantics a la Tackling the awkward squad? I am quite | stumped on this one, so i wont event post my meager | attempts, but rather hope someone brighter then me | will :) We need to add a new Value "FixIO N"... I'd be inclined to do it like this: fixIO m = do { v <- newEmptyMVar ; result <- m (unsafePerformIO (takeMVar v)) ; putMVar v result ; return result } Of course, this just begs the question of what exactly unsafePerformIO might mean, and we can only really answer that when we give an operational semantics to the functional part of the language as well as the imperative part. But perhaps the meaning of fixIO becomes clearer with the above. (Of course an implementation is free to implement it some other way too.) Simon

6 12