In the code: oneChar :: Char -> Doc oneChar c = case lookup c simpleEscapes of Just r -> text r Nothing | mustEscape c -> hexEscape c | otherwise -> char c where mustEscape c = c < ' ' || c == '\x7f' || c > '\xff' simpleEscapes :: [(Char, String)] simpleEscapes = zipWith ch "\b\n...
What is the proper way to safely create a temporary directory in Haskell? System.IO offers ways to create temporary files, but I can't find anything that does the same for directories, neither there nor in System.Directory, System.Posix.Directory, nor System.Posix.Temp. Is there a function I'm overlooking, or do I need to write one mys...
Why I can't construct large tuples in Haskell? Why there's a tuple size limit? Prelude> (1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1,1) <interactive>:1:0: No instance for (Show (t, t1, t2, ... t23)) arising...
I'm in the middle of porting David Blei's original C implementation of Latent Dirichlet Allocation to Haskell, and I'm trying to decide whether to leave some of the low-level stuff in C. The following function is one example—it's an approximation of the second derivative of lgamma: double trigamma(double x) { double p; int i; ...
I've written a small Haskell program to print the MD5 checksums of all files in the current directory (searched recursively). Basically a Haskell version of md5deep. All is fine and dandy except if the current directory has a very large number of files, in which case I get an error like: <program>: <currentFile>: openBinaryFile: resourc...
I have two threads in haskell that perform IO. (They print only). Something like the following: thread1 :: IO () thread1 = putStrLn "One" thread2 :: IO () thread2 = putStrLn "Two" I am currently getting results like the following: OnTwoe OTnweo How can I ensure that each thread completes its IO atomically? ...
What are the similarities and the differences between Haskell's TypeClasses and Go's Interfaces? What are the relative merits / demerits of the two approaches? ...
Hi,I've just completed my freshman year in college and am majoring in EE (with a lot of interest in CS as well) . I know some Python,C/C++ and Java and also a little bit of Actionscript . I am planning to learn either Haskell or Ruby on Rails. Haskell because it is a functional programming language, and I've been really impressed by this...
I've tried this: main = do hSetBuffering stdin NoBuffering c <- getChar but it waits until the enter is pressed, which is not what I want. I want to read the character immediately after user presses it. I am using ghc v6.12.1 on Windows 7. EDIT: workaround for me was moving from GHC to WinHugs, which supports this correctly...
I am a beginner interested in Haskell, and I have been trying to implement the flatmap (>>=) on my own to better understand it. Currently I have flatmap :: (t -> a) -> [t] -> [a] flatmap _ [] = [] flatmap f (x:xs) = f x : flatmap f xs which implements the "map" part but not the "flat". Most of the modifications I make result i...
I am converting some functioning Haskell code that uses Parsec to instead use Attoparsec in the hope of getting better performance. I have made the changes and everything compiles but my parser does not work correctly. I am parsing a file that consists of various record types, one per line. Each of my individual functions for parsing ...
I've got the following problem: I have a tree of objects of different classes where an action in the child class invalidates the parent. In imperative languages, it is trivial to do. For example, in Java: public class A { private List<B> m_children = new LinkedList<B>(); private boolean m_valid = true; public void invalidat...
Hello, I haven't done anything networkish in haskell, so I'm giving that a try now. I'm using Oleg's ZFS as a template how to do that. IIRC he wasn't using threads but was using "delimited continuations" instead so I wonder if a heavier load server app could principally also be written without using forkIO threads. Günther ...
I want to use the itemDoubleClicked(QTreeWidgetItem*,int) signal in a Haskell program I'm writing where I am using qtHaskell for the GUI. To connect a function I have at other places done the following: dummyWidget <- myQWidget connectSlot object signal dummyWidget "customSlot()" $ f Where object is some QWidget and signal is a string...
Why can't Haskell resolve the kind of [[]] (A list of lists)? Why isn't it simply * -> *, as I can give it a type like Int, and get [[Int]], which is of kind *. ...
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 ...
So I keep having this small problem where I have something like func :: a -> b -> [a] -- # or basically any a-> ...-> [a] where ... is any types -> func x y = func' [x] y -- '# as long as they are used to generate a list of [a] from x func' :: [a] -> b -> [a] func' = undefined -- # situation dependant generates a list from ...
I have recently been teaching myself Haskell, and one of my exercises was to re-implement the filter function. However, of all the exercises I have performed, my answer for this one seems to me the most ugly and long. How could I improve it? Are there any Haskell tricks I don't yet know? myfilter :: (a -> Bool) -> [a] -> [a] myfilter f ...
I have heard that in Haskell, creating a multi-threaded application is as easy as taking a standard Haskell application and compiling it with the -threaded flag. Other cases, however, have described the use of a par command within the actual source code. What is the state of Haskell multi-threading? How easy is it to introduce into prog...
I don't know haskell syntax, but I know some FP concepts (like algebraic data types, pattern matching, higher-order functions ect). Can someone explain please, what does this code mean: data Tree ? = Leaf ? | Fork ? (Tree ?) (Tree ?) rotateR tree = case tree of Fork q (Fork p a b) c -> Fork p a (Fork q b c) As I understand, first ...