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• Equivalent of python eval in Haskell

  - by TheMachineCharmer

  There is function in python called eval that takes string input and evaluates it. >>> x = 1 >>> print eval('x+1') 2 >>> print eval('12 + 32') 44 >>> What is Haskell equivalent of eval function?

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• Performance of looping over an Unboxed array in Haskell

  - by Joey Adams

  First of all, it's great. However, I came across a situation where my benchmarks turned up weird results. I am new to Haskell, and this is first time I've gotten my hands dirty with mutable arrays and Monads. The code below is based on this example. I wrote a generic monadic for function that takes numbers and a step function rather than a…

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• Understanding Haskell's filter

  - by dmindreader

  I understand that Haskell's filter is a high order function (meaning a function that takes another function as a parameter) that goes through a list checking which element fulfills certain boolean condition. I don't quite understand its definition: filter:: (a->Bool)->[a]->[a] filter p [] = [] filter p (x:y) | p x = x:filter p y |…

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• Control statements in Haskell?

  - by Nathan

  I am just beginning Haskell, but from all the online tutorials I've found I can't seem to find if there is one accepted way to do a conditional control statement. I have seen if-else, guards, and pattern matching, but they all seem to accomplish the same thing. Is there one generally accepted/faster/more efficient way than the rest?

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• How to get Haskell syntax highlighting on PHP blog

  - by anderstornvig

  Hi, I'm making a blog in PHP and I'd really like to have syntax highlighting on Haskell code. Are there any tools for that out there? I've found hscolour but I don't know if it's possible to integrate it in PHP. I'm using CakePHP if that makes a difference. Thanks.

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• Good Haskell coding standards

  - by Alexey Romanov

  Could someone provide a link to a good coding standard for Haskell? I've found this and this, but they are far from comprehensive. Not to mention that the HaskellWiki one includes such "gems" as "use classes with care" and "defining symbolic infix identifiers should be left to library writers only."

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• What's the status of multicore programming in Haskell?

  - by Don Stewart

  What's the status of multicore programming in Haskell? What projects, tools, and libraries are available now? What experience reports have there been?

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• how to make Random in haskell in pure function

  - by bohuai-jiang

  I want make a haskell function can pick out random number from a given list. there type are randomPick :: [a] - a what should i do ?

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• Infinite loop in haskell? (newbie)

  - by Mike

  I'm just learning Haskell. I thought this would produce a factorial function... (within ghci) Prelude let ft 0 = 1 Prelude let ft n = n * ft (n - 1) Prelude ft 5 (hangs indefinitely, until ^C). Can someone point me in the right direction? Thanks!

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• Why won't the following haskell code compile?

  - by voxcogitatio

  I'm in the process of writing a small lisp interpreter in haskell. In the process i defined this datatype, to get a less typed number; data Number = _Int Integer | _Rational Rational | _Float Double deriving(Eq,Show) Compiling this fails with the following error: ERROR "types.hs":16 - Syntax error in data…

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• Haskell data serialization of some data implementing a common type class

  - by Evan

  Let's start with the following data A = A String deriving Show data B = B String deriving Show class X a where spooge :: a -> Q [ Some implementations of X for A and B ] Now let's say we have custom implementations of show and read, named show' and read' respectively which utilize Show as a serialization mechanism. I want show'…

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• Haskell's TypeClasses and Go's Interfaces

  - by Jeremy Jose

  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?

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• Implementing a very simple 'Wine Rating System' in Haskell

  - by Alex N

  Hello, I have just started learning Haskell and have got stumped on how to add a rating to a custom data type. The data type I'm using has a name, a year and a tuple (userName and their rating), it looks like: data Wine = Wine String Int [Rating] deriving (Eq,Ord,Show,Read) type Rating = (String, Int) I wanted to allow a user to rate a…

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• Haskell - interpreting a number

  - by Abstract

  I have a number 9877342931235. Using Haskell, I need to show it as: 987-734293-123-5 i've tried interspersing the list but of course that puts '-' between every digit. How would I do it to yield the actual result?

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• How to zip multiple lists in Haskell?

  - by TheMachineCharmer

  In python zip function accepts arbitrary number of lists and zips them together. >>> l1 = [1,2,3] >>> l2 = [5,6,7] >>> l3 = [7,4,8] >>> zip(l1,l2,l3) [(1, 5, 7), (2, 6, 4), (3, 7, 8)] >>> How can I zip together multiple lists in haskell?

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• Capturing audio input from microphone, with Haskell?

  - by new guy

  Is there a mature library that could enable audio input and output and work within Haskell? (A nice wrapper is fine, of course.) I'm looking for something that can easily capture microphone input and, perhaps, play various audio files as well. Thanks.

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• Haskell and random numbers

  - by John D.

  Hi, I've been messing with Haskell few days and stumbled into a problem. I need a method that returns a random list of integers ( Rand [[Int]] ). So, I defined a type: type Rand a = StdGen -> (a, StdGen). I was able to produce Rand IO Integer and Rand [IO Integer] ( (returnR lst) :: StdGen -> ([IO Integer], StdGen) ) somehow. Any…

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• Haskell Tuple Size Limit

  - by SHiNKiROU

  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)) …

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• Haskell Binary Tree Function (map)

  - by Bizarro

  How can i define a Haskell function which will apply a function to every value in a binary tree? So i know that it is similar to the map function - and that its type would be: mapT :: (a - b) - Tree a - Tree b but thats about it...

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• Does F# have an equivalent to Haskell's take?

  - by McMuttons

  In Haskell, there is a function "take n list" which returns the first n elements from a list. For example "sum (take 3 xs)" sums up the first three elements in the list xs. Does F# have an equivalent? I expected it to be one of the List-functions, but I can't spot anything that seems to match.

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• Haskell -> After parsing how to work with strings

  - by bito08

  Hello after doing the parsing with a script in Haskell I got a file with the 'appearance' of lists of strings. However when I call the file content with the function getContents or hGetContents, ie, reading the contents I get something like: String with lines (schematically what I want is: "[" aaa "," bbb "" ccc "]" - ["aaa", "bbb"…

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• Haskell "Source reduction"

  - by Martin

  I'm revising for an upcoming Haskell exam and I don't understand one of the questions on a past paper. Google turns up nothing useful fst(x, y) = x square i = i * i i) Source reduce, using Haskells lazy evaluation, the expression: fst(square(3+4), square 8) ii) Source reduce, using strict evaluation, the same expression iii)…

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• Clojure vs Haskell for web applications?

  - by user43737

  I want to learn a functional language that will be good for building web applications in the future. I am choosing between Clojure and Haskell. Which one is a better choice for my purpose?

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• haskell check for user input errors

  - by snorlaks

  Hello. Im writing app in haskell and I would like to know that is the best way to check if users input is ok for example is it int when Im asking for int or if its date when asking for well formed date ? Thanks for help

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• pointers in haskell???

  - by curioComp

  hi, do you know if are there pointers in haskell? -If yes, how do you use them? Are there any problems with them? And why aren't they popular? -If no, is there any reason for it? Please help us!! :) Thank you so much!!

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