pattern-matching

问题 I want to pattern match a map on a key when the second argument is a map with name 's value being the same as the key in the first argument's map. Instead I get this: 8> c(room). room.erl:23: variable 'PlayerName' is unbound error status({_Players, _Tables, ChallengerName}, #{name := ChallengerName}) -> #{status => challenging}; status({#{PlayerName := PlayerStatus}, _, _}, #{name := PlayerName}) -> PlayerStatus; status(_, _) -> #{status => null}. Oddly, the first function declaration works

问题 I'm trying to write a function that takes a square grid of letters and given a word to find from a list of words, it searches for it horizontally, vertically or diagonally (also looking backwards in each case). I've tried writing this function in various ways with no success so was wondering if my general algorithm sounded ok and implementable. Return co-ordinates for everywhere the first letter of the word occurs so something like [row,col] = find(grid==words(2)) with words being the list of

问题 As a beginner, I would like to know if there is a way to write below query in redis Scan 0 MATCH Test:[keyword*:* | *:keyword] Right now I have to do two separate scans for this query as below Scan 0 MATCH Test:*:keyword* Scan 0 MATCH Test:keyword*:* 回答1: I see that you've 3 choices here: Wrap both commands into a Lua script and call it as it would be a single command. Instead of scanning do indexing . Create a set or sorted set where you'll store all elements that matches these patterns, and

问题 I have the following type, and would like to make it a Functor: newtype SubsM a = SubsM {runSubsM :: Context -> Either Error (a, Env)} So far i got this instance Functor SubsM where fmap f (SubsM a) = SubsM (\s->(Right((f a),(fst s)))) I get an error because a is not the expected type, my question is how do i pattern match a on the left-hand side? 回答1: You can pattern match on the Either Error (a, Env) with case : instance Functor SubsM where fmap f (SubsM cf) = SubsM $ \c -> case (cf c) of

问题 This is a real part of my work. In order to keep students' paper follow given format standard, I have to judge the reference type in students' papers, separate its items(author, title, magazine name, year, etc), then give modification advice if some item is missing. It is tedious, so after some years' of work-by-people, I get too tired. I think to do it by programming. In a paper, many kinds of references will be citation, for example, Journal paper, Dissertation paper, book and so on. They

问题 In functional language like OCaml, we have pattern matching. For example, I want to log users' actions on my website. An action could be 1) visiting a web page, 2) deleting an item, 3) checking the profile of another user, etc. In OCaml, we can write something as follows: type Action = | VisitPage of string (* www.myweb.com/help *) | DeletePost of int (* an integer post id *) | ViewUser of string (* a username *) However, I am not sure how to define this Action in JavaScript. One way I could

问题 I'm trying to parse the csv files and I need to determine the type of each field starting from its string value. for examples: val row: Array[String] = Array("1/1/06 0:00","3108 OCCIDENTAL DR","3","3C","1115") this is what I would get: row(0) --> Date row(1) --> String row(2) --> Int Ecc.... how can I do? ------------------------------------ SOLUTION ------------------------------------ This is the solution I've found to recognize the fields String, Date, Int, Double and Boolean. I hope that

问题 is there a regular expression to match the content within braces. For example with the following: d = {'key': {'a': [1,2,3]}} I would want to match {'key': {'a': [1,2,3]}} and {'a': [1,2,3]} , but not {'key': {'a': [1,2,3]} 回答1: In classical regular expressions, this is impossible - DFAs can't parse nested pairs. There are ways to do it with extended regular expressions, such as recursive expressions that are allowed in some regex engines (such as Perl regex), but they're not always pretty. (

问题 if i have a class that accepts a Type argument for example Seq[T] , and i've many objects of this class. and i want to split them depending on type Argument T for example : val x = List(Seq[Int](1,2,3,4,5,6,7,8,9,0),Seq[String]("a","b","c")) x.foreach { a => a match{ case _ : Seq[String] => print("String") case _ : Seq[Int] => print("Int") } } the result of this code is StringString . it only matches the class Seq not the Type also , what should i do to force it to match the Type ? 回答1: What

问题 F# assigns function arguments via pattern matching. This is why // ok: pattern matching of tuples upon function call let g (a,b) = a + b g (7,4) works: The tuple is matched with (a,b) and a and b are available directly inside f. Doing the same with discriminated unions would be equally beneficial, but I cannot get it to done: // error: same with discriminated unions type A = | X of int * int | Y of string let f A.X(a, b) = a + b // Error: Successive patterns // should be separated by spaces