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  • Is functional GUI programming possible?

    - by eman
    I've recently caught the FP bug (trying to learn Haskell), and I've been really impressed with what I've seen so far (first-class functions, lazy evaluation, and all the other goodies). I'm no expert yet, but I've already begun to find it easier to reason "functionally" than imperatively for basic algorithms (and I'm having trouble going back where I have to). The one area where current FP seems to fall flat, however, is GUI programming. The Haskell approach seems to be to just wrap imperative GUI toolkits (such as GTK+ or wxWidgets) and to use "do" blocks to simulate an imperative style. I haven't used F#, but my understanding is that it does something similar using OOP with .NET classes. Obviously, there's a good reason for this--current GUI programming is all about IO and side effects, so purely functional programming isn't possible with most current frameworks. My question is, is it possible to have a functional approach to GUI programming? I'm having trouble imagining what this would look like in practice. Does anyone know of any frameworks, experimental or otherwise, that try this sort of thing (or even any frameworks that are designed from the ground up for a functional language)? Or is the solution to just use a hybrid approach, with OOP for the GUI parts and FP for the logic? (I'm just asking out of curiosity--I'd love to think that FP is "the future," but GUI programming seems like a pretty large hole to fill.)

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  • How can I implement a splay tree that performs the zig operation last, not first?

    - by Jakob
    For my Algorithms & Data Structures class, I've been tasked with implementing a splay tree in Haskell. My algorithm for the splay operation is as follows: If the node to be splayed is the root, the unaltered tree is returned. If the node to be splayed is one level from the root, a zig operation is performed and the resulting tree is returned. If the node to be splayed is two or more levels from the root, a zig-zig or zig-zag operation is performed on the result of splaying the subtree starting at that node, and the resulting tree is returned. This is valid according to my teacher. However, the Wikipedia description of a splay tree says the zig step "will be done only as the last step in a splay operation" whereas in my algorithm it is the first step in a splay operation. I want to implement a splay tree that performs the zig operation last instead of first, but I'm not sure how it would best be done. It seems to me that such an algorithm would become more complex, seeing as how one needs to find the node to be splayed before it can be determined whether a zig operation should be performed or not. How can I implement this in Haskell (or some other functional language)?

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  • Enable --hyperlink-source for "cabal install"

    - by Tener
    The command cabal haddock has very useful --hyperlink-source option. I would like to have the source hyperlinked when building documentation with cabal install. The ticket #517 seems to be just about it: http://hackage.haskell.org/trac/hackage/ticket/517 However, perhaps it is possible to set this flag via ~/.cabal/config file? If not, how can I get working cabal-install build with the patch from #517 without installing Cabal-0.9, which is currently mandatory (due to one patch from December)?

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  • Enable --hyperling-source for "cabal install"

    - by user263407
    The command cabal haddock has very useful --hyperlink-source option. I would like to have the source hyperlinked when building documentation with cabal install. The ticket #517 seems to be just about it: http://hackage.haskell.org/trac/hackage/ticket/517 However, perhaps it is possible to set this flag via ~/.cabal/config file? If not, how can I get working cabal-install build with the patch from #517 without installing Cabal-0.9, which is currently mandatory (due to one patch from December)?

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  • GHCi error: Not in scope

    - by dmindreader
    I'm trying to compile this function from Learn You a Haskell for Great Good. removeNonUppercase st = [ c | c <- st, c `elem` ['A'..'Z']] by placing it into a removeNonUpperCase.hs file. It compiles fine, but when passing the argument: ghci> removeNonUppercase "Hahaha! Ahahaha!" the compiler says: <interactive>:1:0: Not in scope: 'removeNonUpperCase' Why?

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  • ghc-pkg vs cabal

    - by Ben Lever
    In relation to how packages are created, installed and used in Haskell, what are the differences between ghc-pkg and cabal? When would you use one or the other or both? Are they complementary tools, competitive tools, or simply tools that do different jobs?

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  • Why must recursion be in a separate file in hugs?

    - by Casebash
    In Haskell in 5 steps the factorial function is defined as follows: let fac n = if n == 0 then 1 else n * fac (n-1) But for hugs, it says that fac needs to be in fac.h. Can anyone explain why this is the case - missing the ability to define recursion seems like a massive limitation for an interpreter.

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  • Generics and Constrained Polymorphism versus Subtyping

    - by Rahul G
    Hullo all. In this (Warning: PDF) presentation on Haskell Type Classes, on slide #54, there's this question: Open Question: In a language with generics and constrained polymorphism, do you need subtyping too? My questions are: How do generics and constrained polymorphism make subtyping unnecessary? If generics and constrained polymorphism make subtyping unnecessary, why does Scala have subtyping?

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  • List of GHC extensions

    - by yairchu
    I wanted to use {-# LANGUAGE OverloadedStrings #-} but I forgot how it's called. This kind of thing isn't hoogle-able, and also it takes some time finding using google*. Is there somewhere a list of GHC extensions named as they are in the LANGUAGE pragma? * My googling search journey: Google Haskell at wikipedia GHC at wikipedia GHC language features Overload string literals OverloadedStrings

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  • run wxHaskell on other machine

    - by snorlaks
    Hello, I've compiled haskell program which uses wxHaskell library, now I would like to know how to make it run on other machines which doesn't have wxHaskell installed. Of course I can see errors and I can copy dlls written in output and copy them to that machine but what is professioal sollution, can I write any installer or something like that? thanks for help

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  • How can my-program.hs get its version number from my-program.cabal at build time?

    - by Dave Hinton
    I would like my cabalised program to have a --version switch. I would like it to report the same version as is present in the .cabal file. If I have to update the version number separately in my Haskell source code as well as in the .cabal file, I will eventually get them out of sync. So, how can my program, while being compiled under cabal, get its version number from the .cabal file?

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  • Higher-kinded Types with C++

    - by Venkat Shiva
    This question is for the people who know both Haskell (or any other functional language that supports Higher-kinded Types) and C++... Is it possible to model higher kinded types using C++ templates? If yes, then how?

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  • How can I compile a GUI executable with ghc?

    - by martingw
    I ported a little Haskell program I wrote from Mac to Windows. It's a GUI application (wxHaskell, compiled with ghc 6.12.1), so it does not need the command prompt window to open. It does so, anyway, so my question: What must I do so that the program starts without opening a prompt window first? Is there some ghc switch for this?

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  • Emacs align-regexp on = but not ==

    - by Karl
    I am working in Haskell and frequently come across code similar to the following: func i j | i == j = i | otherwise = j I want to align on the '=' character using align-regexp but don't have the elisp knowhow. I have tried just doing " = " without the quotes, but this inserts an unwanted space character before each '='. I have found a proposed solution here but I can't seem to get that to do anything at all. Please help me write a function or hard-coded macro that will allow me to set a keybinding for this.

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  • Scala Hoogle equivalent?

    - by Alexey Romanov
    Hoogle allows you to search many standard Haskell libraries by either function name, or by approximate type signature. I find it very useful. Is there anything like Hoogle for Scala? Search in ScalaDoc 2 only finds types and packages by name.

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  • Outputing UTF-8 string on Mac OS's Terminal

    - by SuperBloup
    I got a programm in haskell outputting utf-8 using the package utf8-string and using only the output functions of this package. I set the encoding of each file I write to this way : hSetEncoding myFile utf8 {- myFile may be stdout -} but when I try to output : alpha = [fromEnum 0x03B1] {- a -} instead of the nice alpha letter I got on Linux (or in a file on windows), I got the following : α The weird thing is even if I try to write the output on a file, I can't read it back with mvim as an utf-8 file. Is there any way to get the correct behaviour

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  • Is there a suitable replacement for C++, when I would like to write video processing applications?

    - by Nisanio
    Hi I want to write a video editing software, and the "logical" conclusion is that the language I must to use is C++... But I don't like it (sorry c++ fans) I would like to write it with something cool, like Lisp or Haskell or Erlang... But I don't know if the open source implementation of those languages (I don't have money to buy licenses) let me made a competitive software (in the performance area) What do you think? what do you recommend?

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  • Where are the clever uses of strict evaluation?

    - by devonrt
    It seems like there are plenty of examples of clever things being done in a lazily-evaluated language that can't be done in an environment with strict evaluation. For example infinite lists in Haskell or replacing every element in a tree with the tree's minimum value in one pass. Are there any examples of clever things being done in a strictly-evaluated language that can't easily be done in a lazily-evaluated language?

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