- Haskell-Cafe - Haskell.org

NewLines in string
by Serge D. Mechveliani 04 Oct '08

04 Oct '08

People, Here is a certain naive question about string setting in a Haskell program. I have the functions parseProgram :: String -> Program apply :: Program -> Term -> Term -- interpreter, and try to build the example modules for them as in the following example: ---------------------------------------------------------------- module Main where program = parseProgram " isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo " main = let {data = ... :: Term; res = apply program data} in putStr $ concat ["data = ", shows data "\n", "res = ", shows res "\n"] ---------------------------------------------------------------- -- that is set a string (an object program example), parse it to a program, apply this program and print the result. But in reality, the above string must be set like this: (2) "\ \ isOrdered nil -> true;\ \ isOrdered (X:nil) -> true;\ \ isOrdered (X:Y:Ys) -> \ \ isOrd (X > Y) (isOrdered (Y:Ys));\ \\ \ isOrd true bo -> false;\ \ isOrd false bo -> bo\ \" -- because otherwise Haskell treats the NewLine characters in the above string in an unneeded way. But with (2), the program Main occurs hard to read. One could try to improve this by using readFile. Form the file data.txt -------------------------------- isOrdered nil -> true; isOrdered (X:nil) -> true; isOrdered (X:Y:Ys) -> isOrd (X > Y) (isOrdered (Y:Ys)); isOrd true bo -> false; isOrd false bo -> bo ----------------------------------------- and combine readFile "data.txt", the `do' construct, pearseProgram, apply, putStr. But this needs adding one more file, and this also changes the programming style in defining examples. Now, what is the difference? 1. readFile reads string from file, with treating NewLine as needed. 2. The Haskell compiler reads the expression parseProgram " isOrdered nil > true; ... " from the input Haskell program with treating NewLine in the string in a different way. I wonder: how to remove most of backslashes in the program (2) ? Thank you in advance for your comments. ----------------- Serge Mechveliani mechvel(a)botik.ru

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maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Hello, Here is a site I discovered a while back for another language ... I guess in the back of my mind this more where I was going vis-a-vis scientific computing .... http://www.enthought.com/ Kind regards, Vasili

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Re: [Haskell-cafe] maybe a goal and challenge for the Haskell in terms of scientific computing
by Galchin, Vasili 04 Oct '08

04 Oct '08

Let me recuse myself .... What is the nature of the open source license? Vasili On Fri, Oct 3, 2008 at 8:39 PM, Jeff Wheeler <jeff(a)nokrev.com> wrote: > On Oct 3, 2008, at 8:26 PM, Galchin, Vasili wrote: > > Here is a site I discovered a while back for another language ... I >> guess in the back of my mind this more where >> I was going vis-a-vis scientific computing .... http://www.enthought.com/ >> > > I interned at Enthought over this last summer; it's a very cool place. Many > of the open-source scientific libraries could be rewritten in Haskell > without significant difficulty, and this actually seems like a decent idea. > > SciPy and NumPy are the two most significant libraries worth thinking > about, in my opinion. Some of the other software, e.g. Traits, is less > relevant to scientific software in the context of Haskell. > > Much of their stack, especially Traits, TraitsGUI, and application > libraries are designed to help write applications quickly without much > programming experience. With these tools, it's easy for scientists, without > knowing much Python, to write large programs that work well for most of > their purposes. > > Jeff Wheeler >

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Announcing OneTuple-0.1.0
by John Dorsey 04 Oct '08

04 Oct '08

Fellow Haskellers, Much attention has been paid over the years to the regrettable omission of singleton tuples from Haskell. I am pleased to announce OneTuple, a humble implementation of the singleton tuple for Haskell. Now you can: * Wrap a single value of any type in a OneTuple ! * Pattern match to retrieve your value ! * Solve any of the software problems that cannot be solved without the singleton tuple ! * Enjoy instances for all the classes normal tuples have, plus more ! * Proclaim feature parity with Python ! Note: the singleton tuple does not support tuple syntax. Contributions are welcome. The project could use a tutorial, and a decent test suite. Strict singleton tuples are planned for the next version. Enjoy! Regards, John Dorsey

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pure Haskell database
by Manlio Perillo 04 Oct '08

04 Oct '08

Hi. I need a simple, concurrent safe, database, written in Haskell. A database with the interface of Data.Map would be great, since what I need to to is atomically increment some integer values, and I would like to avoid to use SQLite. Thanks Manlio Perillo

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having fun with GADT's
by Anatoly Yakovenko 03 Oct '08

03 Oct '08

I dont remember where i saw it, but i think someone had an example of a list whose type is the maximum element in the list. I've been trying to reproduce that with GADT's. data One = One data Two = Two data Three = Three data MaxList t where Elem1 :: MaxList One Elem2 :: MaxList Two ML1Cons1 :: MaxList One -> MaxList One -> MaxList One ML1Cons2 :: MaxList One -> MaxList Two -> MaxList Two ML2Cons1 :: MaxList Two -> MaxList One -> MaxList Two ML2Cons2 :: MaxList Two -> MaxList Two -> MaxList Two a = ML2Cons2 Elem2 $ ML2Cons1 Elem2 $ ML1Cons1 Elem1 $ Elem1 so one problem is the tedium of defining a cons for each possible combination. The other problem is that i cant define a usefull tail that makes any sense. mlTail :: MaxList Two -> MaxList t mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b this one doesn't work, and probably because there is nothing that i could do with the return value. mlTail :: MaxList Two -> MaxList Two mlTail (ML2Cons2 a b) = b mlTail (ML2Cons1 a b) = b --wont compile because b is a MaxList One will only work for lists that only contain Two's, which is not what i want either. So is this somehow possible? Thanks

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Building gtkhs, OpenSolaris x86
by Lally Singh 03 Oct '08

03 Oct '08

Hey folks, I know it seems an obtuse OS to build on, but trust me, it's pretty nice despite the hassles. I'm getting these three errors (repeated a few times) while building gtkhs-0.9.13 on ghc 6.8.3, and was hoping for any suggestions on where to go from here: tools/c2hs/base/general/Map.hs:16:7: Could not find module `Data.Map': it is a member of package containers-0.1.0.2, which is hidden tools/c2hs/base/errors/Errors.hs:44:0: Failed to load interface for `Position': Use -v to see a list of the files searched for. glib/System/Glib.hs:13:0: Failed to load interface for `System.Glib.UTFString': Use -v to see a list of the files searched for. What did I screw up? Is there something else I should load? Maybe an older version of gtkhs? ghc? Thanks for any help! -- H. Lally Singh Ph.D. Candidate, Computer Science Virginia Tech

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Alex and Flex
by Manlio Perillo 03 Oct '08

03 Oct '08

Hi. I'm starting to write a CSS parser with Alex and Happy. The grammar is defined here: http://www.w3.org/TR/CSS21/grammar.html However I have noted that there are some difference in the syntax between Alex and Flex? What is the rationale? One more thing. Here: http://www.haskell.org/alex/doc/html/alex-files.html it seems that there is an error with macrodef := @smac '=' set | @rmac '=' regexp it should be macrodef := $smac '=' set | @rmac '=' regexp Thanks Manlio Perillo

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Monoids [Stacking monads]
by Andrew Coppin 03 Oct '08

03 Oct '08

Ryan Ingram wrote: > Newtypes is the general (& sadly unsatisfactory) answer: > Oh dear. Well that _is_ pretty unsatisfactory... Given the constraints of the Haskell type system, could we do better in principle?

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Source of 16x16 Sudokus?
by Murray Gross 03 Oct '08

03 Oct '08

Folks: For research on the behavior of parallel Haskell, does anyone know of a source for graded (easy through evil) 16x16 Sudoku puzzles? Our hardware runs too fast for us to get meaningful timings on 9x9's. I suppose we could insert time wasters, but I think that would also distort the results . . . . Thanks in advance, Murray Gross Brooklyn College

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