arrows

问题 So I'll break my question into 4 parts, but first some background: I feel relatively comfortable with Monads, but not very comfortable with Arrows. I suppose the main problem I have with them is, I don't see what they are useful for. Whether formally correct or not, I understand Monads to be a tool that allows us to introduce side effects from computation. As they generalize program fragments from pure values to values boxed with other actions. From my shotgun "read all the papers" approach

问题 I have drawn a trajectory plot in python using matplotlib of a boat like so: Now I want to add some arrows, like wind direction, true heading etc. However I want the arrows to have the same size no matter which zoom-level the plot is at. I tried matplotlib.pyplot.arrow, however there I have to define the length of the arrows. I could make matplotlib.pyplot.arrow work, but then I'd have to get the height and width of the plot, and scale my arrows accordingly, so I wondered if there was a

问题 I’m trying to parse some XML files with Haskell. For this job I’m using HXT to get some knowledge about arrows in real world applications. So I’m quite new to the arrow topics. In XPath (and HaXml) it’s possible to select a node by position, let’s say: /root/a[2]/b I can’t figure out how to do something like that with HXT, even after reading the documentation again and again. Here is some sample code I’m working with: module Main where import Text.XML.HXT.Core testXml :: String testXml =

问题 I am using zurb foundation orbit slideshow. The next and the prev buttons or links on the left and right edge of the page is the default black triangle. Please have a look at this test page: http://www.endsnore.com/_test1b/index.aspx How do I customize the next and prev buttons or links? How do I add my own arrow code: ‹ and › OR add my own custom arrow images like these orange left and right arrows here: http://www.getaveo.com/index.aspx Please provide exact code example. I would appreciate

问题 According to the famous paper Idioms are oblivious, arrows are meticulous, monads are promiscuous, the expressive power of arrows (without any additional typeclasses) should be somewhere strictly between applicative functors and monads: monads are equivalent to ArrowApply , and Applicative should be equivalent to something the paper calls "static arrows". However, it is not clear to me what restriction this "static"-ness means. Playing around with the three typeclasses in question, I was able

问题 According to the famous paper Idioms are oblivious, arrows are meticulous, monads are promiscuous, the expressive power of arrows (without any additional typeclasses) should be somewhere strictly between applicative functors and monads: monads are equivalent to ArrowApply , and Applicative should be equivalent to something the paper calls "static arrows". However, it is not clear to me what restriction this "static"-ness means. Playing around with the three typeclasses in question, I was able

问题 In arrow do notation, you can use the rec keyword to write recursive definitions. So for example: rec name <- function -< input input <- otherFunction -< name How can this ever evaluate? It seems like it would just go into an infinite loop or something. I know it evaluates to the loop arrow combinator, but I don't understand how that works either. EDIT: that powers example is really helpful. How would you write that with do notation, though? I assume you would need to use rec. 回答1: This bit

问题 I'm creating a graph in JavaFX which is supposed to be connected by directed edges. Best would be a bicubic curve. Does anyone know how to do add the arrow heads? The arrow heads should of course be rotated depending on the end of the curve. Here's a simple example without the arrows: import javafx.application.Application; import javafx.scene.Group; import javafx.scene.Scene; import javafx.scene.paint.Color; import javafx.scene.shape.CubicCurve; import javafx.scene.shape.Rectangle; import

问题 I'm trying to get my head around HXT, a Haskell library for parsing XML that uses arrows. For my specific use case I'd rather not use deep as there are cases where <outer_tag><payload_tag>value</payload_tag></outer_tag> is distinct from <outer_tag><inner_tag><payload_tag>value</payload_tag></inner_tag></outer_tag> but I ran into some weirdness that felt like it should work but doesn't. I've managed to come up with a test case based on this example from the docs: {-# LANGUAGE Arrows,

问题 I recently found out that it is possible to add greek alphabets and other symbols within the annotate text in ggplot. I am trying to add arrows (upwards and downwards) to my text and I can't seem to find the correct numerical code for it. I tried searching but can't find a list of codes online. The syntax is something like that under label: label="'test text ' * symbol('\\205')" \142 gives a beta symbol and \154 gives a gamma symbol. Anyone knows how does this code works? Thanks! 回答1: The