I have the following expression: getCount :: (Num a) => a -> [a] getCount int = foldl processOneCount [0,0,0,0,0,0,0,0,0,0] (map (singleDigitCount) (map (digitToInt) (show int))) and i get the following error: Couldn't match expected type `a' against inferred type `Int' `a' is a rigid type variable bound by ...
Full source here: http://www.vim.org/scripts/download_script.php?src_id=10391 The line is: silent %s/[^λ←→≲≳≡≠⇒»∙∀\\\-!#$%&*+/<=>?@\^|~.]\@<=\\\([^λ←→≲≳≡≠⇒»∙∀\\\-!#$%&*+/<=>\?@\^|~.]\)/λ\1/eg Someone please decipher this for me. The larger script is intended to unicode-ify some operators in Haskell into more familiar mathematical...
Say i have a function prototype as follows: func :: [Int] -> [Int] How is it possible to enforce only a non-negative list of integers as input arguments? I would have to change the param type from [Int] to what.. ? At this fair moment it works with func [-1,-2], i only want it to work with [1,2] i.e. with the interpreter spewing the er...
Consider the following piece of Haskell code: type Parser a = String -> [(a, String)] item :: Parser Char item = \ inp -> case inp of [] -> [] (x:xs) -> [(x, xs)] ret :: a -> Parser a ret v = \ inp -> [(v, inp)] parse :: Parser a -> String -> [(a, String)] parse p inp = p inp pseq :: Parser ...
Pattern matching is one of the most elegant Haskell features. I've been working on a project recently where I need a queue data structure so I'm using Data.Sequence. However, it looks like I have to give up the elegance of pattern matching and resort to guards: floodFillWorker :: Image -> RGBAColor -> Double -> PixelQueue -> Image fl...
I am attempting to create a stack of monad transformers and am having trouble getting the correct type signatures for my functions. (I'm still pretty new to Haskell) The stack combines multiple StateT transformers since I have multiple states I need to keep track of (two of which could be tupled, but I'll get to that in a second) and a ...
I've been looking at Haskell lately and it seems like a very nice way to watch programming problems from an alternative point of view - alternative to my usual imperative (I have a strong C++ background) view, at least. However, all the articles I see seem to deal with the same kinds of programming problems: Parsers Compilers Numeric ...
I'm going out of my mind trying to simply output UTF-8-encoded data to the console. I've managed to accomplish this using String, but now I'd like to do the same with ByteString. Is there a nice and fast way to do this? This is what I've got so far, and it's not working: import Prelude hiding (putStr) import Data.ByteString.Char8 (put...
Hi, I've been playing with newtype wrappers for my indexes to avoid bugs, and I have some code like this: {-# LANGUAGE GeneralizedNewtypeDeriving #-} newtype PersonIdx = PersonIdx Int deriving (Enum, Eq, Integral, Num, Ord, Real, Show) To derive Integral, one must derive all its dependencies as well (hence the above list of type-cl...
Completely stumped. Can't make sense of any of the documentation. Can someone please provide an example of how I can parse the following shortened exiftool output using the Haskell module Text.JSON? The data is generating using the command exiftool -G -j <files.jpg>. [{ "SourceFile": "DSC00690.JPG", "ExifTool:ExifToolVersion": 7.8...
I've managed to use Parsec to parse a String, but cannot manage to do the same with a ByteString. How can I make Parsec work with ByteStrings without manually converting them to Strings? I get the feeling this isn't hard to accomplish. Am I wrong? (I'm new to Haskell. ^^) Thanks! ...
I have a small numerical simulation in C (I had to do it in C to share it with my advisor) but I want to use a "haskell script" like thing to organize the simulation. The program accepts some command line arguments and spits some output I'd like to redirect to a file, so I did something like this: import Control.Monad import System.Pr...
i'm trying to define the isInfixOf function, and i came to a solution(hope it works good :-)), but because of the recursion nature of haskell, i wrote another (help) function that almost duplicate the code of the function isInfixOf. this is the code: myIsInfixOf :: (Eq a) => [a] -> [a] -> Bool myIsInfixOf [] [] = True myIsInfixOf [] ...
Trying to learn Haskell. I am trying to write a simple function to remove a number from a list without using built-in function (delete...I think). For the sake of simplicity, let's assume that the input parameter is an Integer and the list is an Integer list. Here is the code I have, Please tell me what's wrong with the following code a...
Is there a way to use the TDFA implementation of Regex with the functions in Text.Regex such as subRegex? The documentation says that Text.Regex must use the POSIX implementation only. ...
Say I have x = Just 2 Is there a way (preferrably a builtin mechanism/function) to use x in a single statement such that if it is a Just, then the 2 is automatically unwrapped and used, and if it is a Nothing, an exception is raised? That is, (f x) + 2 == 4 if x == Just 2, and raises an exception if x == Nothing. ...
if i have somthing like that: func (x1:x2:x3:xs) = xs then x1,x2,x3 must exist, yes? they can't be [], but must(again, MUST) be with a value, yes? also, the xs can be [] or [a] or [a,a,a] (etc'), yes? (in [a] i mean that it's a list with one number, and [a,a,a] is list of three numbers). also i have function that define isPrefixOf: m...
In a recent answer to a style question, I wrote main = untilM (isCorrect 42) (read `liftM` getLine) and isCorrect num guess = case compare num guess of EQ -> putStrLn "You Win!" >> return True ... Martijn helpfully suggested alternatives: main = untilM (isCorrect 42) (read <$> getLine) EQ -> True <$ putStrLn "You Win!" ...
I have a f function with signature f :: [a] -> StateT Int Reader b [c], and f' with signature f' :: a -> StateT Int Reader b [c] The computation in f (very simplified) looks like that: f [] = return [] f (s:st) = f' s >>= \x -> f st >>= \y -> return $ ... And in place of the ... I would like to return the [c] pa...
I'm needing some Ints to use as seed to random number generation and so I wanted to use the old trick of using the system time as seed. So I tried to use the Data.Time package and I managed to do the following: import Data.Time.Clock time = getCurrentTime >>= return . utctDayTime When I run time I get things like: Prelude Data.T...