haskell

问题 I'm a beginner trying to learn more about Haskell and Aeson by parsing some json files I find online. I have a .json that looks like this "Abilities": { "Prime": { "Ammo": 210, "Available": true, "Diposition": 3, "Type": "Secondary", "Class": "Pistols", "NormalAttack": { "Chance": 0.25, "Streak": 2, "Rate": 2.67, "ShotType": "Hit-Scan", "Damage": { "Front": 15, "Back": 15, "Up": 120, "Down": 40 }, "Status": 0.25 } "Accuracy": 9.8, "Reload": 3, "Name": "Prime", "Magazine": 16, }, "Dual": {

问题 Where is the OpenGL function for loadMatrixf and what is the type signature? 回答1: See the Matrix class. I think you are looking for either newMatrix or the matrix StateVar in those docs. For example: let mat be a list of 16 floats representing the matrix. Then you would use it something like this: import qualified Graphics.Rendering.OpenGL.GL as GL drawThingWithMatrix :: [GL.GLfloat] -> IO () drawThingWithMatrix mat = GL.preservingMatrix $ do -- instead of push/pop newmat <- GL.newMatrix GL

问题 I am trying to work out a data structure for the following situation. Graph Structure I plan to have a graph of nodes with un-weighted, directed edges: Graph = [Node] Each node has: Some TBD internal (persistent) state A queue of incoming messages A type of message it can send determined by a function that accepts the current node state (with the possibility of failure) A list of edges Node { nodeState :: NodeState, inbox :: Queue NodeMessage, nodeMessage :: (NodeState -> Maybe NodeMessage),

问题 I am trying to work out a data structure for the following situation. Graph Structure I plan to have a graph of nodes with un-weighted, directed edges: Graph = [Node] Each node has: Some TBD internal (persistent) state A queue of incoming messages A type of message it can send determined by a function that accepts the current node state (with the possibility of failure) A list of edges Node { nodeState :: NodeState, inbox :: Queue NodeMessage, nodeMessage :: (NodeState -> Maybe NodeMessage),

问题 I want to make two div's float side by side using Obelisk. For this I used the information from this post, How to place div side by side and for this solution classes have to be declared in css. Following the advice of this tutorial (https://github.com/hansroland/reflex-dom-inbits/blob/master/tutorial.md), more specifically the part about mainWidgetWithHead, I put the commands in a different file. The problem is, however, that I can't find where the css-file should be stored in order to get

问题 I get the error Ambiguous type variable `p0' in the constraints: (Show p0) arising from a use of `print' at cwqr_0003.hs:31:6-10 (Ord p0) arising from a use of `PSQ.lookup' from the code below. I have no idea how to analyze this. Could this be a problem in GHC or in one of the modules? If I try putStr in place of print then I get an error related to the expected type being a string rather then maybe p0. When I try fromMaybe it gives me an error related to the default value literal zero that I

问题 If I create a cabal sandbox with cabal sandbox init , I can use cabal repl or cabal exec ghc(i) to work with those packages without creating a project: $ mkdir /tmp/example && cd /tmp/example $ cabal sandbox init $ cabal install QuickCheck $ cabal exec ghci Prelude> :m Test.QuickCheck Prelude Test.QuickCheck> However, if I change the path to something else, even to a subdirectory, I cannot access the packages anymore: $ mkdir -p /tmp/example/sub && cd /tmp/example/sub $ cabal exec ghci

问题 I've just started playing with GHCi. I see that list generators basically solve an equation within a given set: Prelude> [x | x <- [1..20], x^2 == 4] [2] (finds only one root, as expected) Now, why can't I solve equations with results in ℝ, given that the solution is included in the specified range? [x | x <- [0.1,0.2..2.0], x*4 == 2] How can I solve such equations within real numbers set? Edit: Sorry, I meant 0.1 , of course. 回答1: As others have mentioned, this is not an efficient way to

问题 I'm a Haskell newbie, so chances are I've missed something obvious... I am trying to write a generic colour quantisation algorithm using ad hoc polymorphism. However, I'm having some trouble getting my data out with pattern matching (I've not actually got to the quantisation bit, yet). I can't describe this succinctly, so here's a simplified version of my code which exhibits the problem: {-# LANGUAGE FlexibleInstances #-} import Data.Word type ColourGrey = Word8 data ColourRGB = ColourRGB

问题 THe below is the content of the vagrant file. When I run vagrant up command, it installs cabal as required but it is in the root directory. Hence, it becomes unusable. I want to update the cabal version to latest version using cabal update . But it is not happening. Finally, in my VM, I have old version of cabal which comes with haskell-platform which is of no use to me. However, when I execute these commands separately by explicitly logging into VM, and not putting anything in Vagrantfile,