functional-programming

问题 I am generating an an array of categories and subcategories in my Laravel API for use in my client side app. I'm doing this by using the collection's filter and map methods to organize the data pulled from the database: // get the data from the category table $categoryData = $categories->all()->categories(); // filter the data by category names we know we want and create the multi-dimensional array of the fields we need $categoryList = $categoryData->filter(function ($value) { return $value[

问题 although i understand the implementation of the reader monad of which i give 2 of the most prominent way to do it below case class Reader[R, A](run: R => A) def readerMonad[R] = new Monad[({type f[x] = Reader[R,x]})#f] { def unit[A](a: => A): Reader[R, A] = Reader(_ => a) override def flatMap[A,B](st: Reader[R, A])(f: A => Reader[R, B]): Reader[R, B] = Reader(r => f(st.run(r)).run(r)) } or more simply case class Reader[R, A](run: R => A) { def map[B](f: A => B): Reader[R, B] = Reader(r => f

问题 although i understand the implementation of the reader monad of which i give 2 of the most prominent way to do it below case class Reader[R, A](run: R => A) def readerMonad[R] = new Monad[({type f[x] = Reader[R,x]})#f] { def unit[A](a: => A): Reader[R, A] = Reader(_ => a) override def flatMap[A,B](st: Reader[R, A])(f: A => Reader[R, B]): Reader[R, B] = Reader(r => f(st.run(r)).run(r)) } or more simply case class Reader[R, A](run: R => A) { def map[B](f: A => B): Reader[R, B] = Reader(r => f

问题 although i understand the implementation of the reader monad of which i give 2 of the most prominent way to do it below case class Reader[R, A](run: R => A) def readerMonad[R] = new Monad[({type f[x] = Reader[R,x]})#f] { def unit[A](a: => A): Reader[R, A] = Reader(_ => a) override def flatMap[A,B](st: Reader[R, A])(f: A => Reader[R, B]): Reader[R, B] = Reader(r => f(st.run(r)).run(r)) } or more simply case class Reader[R, A](run: R => A) { def map[B](f: A => B): Reader[R, B] = Reader(r => f

问题 Using code from this answer, I have (defn repeat-image [n string] (println (apply str (repeat n string)))) (defn tile-image-across [x filename] (with-open [rdr (reader filename)] (doseq [line (line-seq rdr)] (repeat-image x line)))) ...to tile an ascii image horizontally. Now, how would I be able to "ignore" the first line? The reason I'm doing this is each image has the coordinates (for example "20 63") as the first line, and I don't need the line. I tried some ways (keeping an index,

问题 Suppose I have a custom type wrapping an existing type, newtype T = T Int deriving Show and suppose I want to be able to add up T s, and that adding them up should result in adding the wrapped values up; I would do this via instance Num T where (T t1) + (T t2) = T (t1 + t2) -- all other Num's methods = undefined I think we are good so far. Please, tell me if there are major concerns up to this point. Now let's suppose that I want to be able to multiply a T by an Int and that the result should

问题 Suppose I have a custom type wrapping an existing type, newtype T = T Int deriving Show and suppose I want to be able to add up T s, and that adding them up should result in adding the wrapped values up; I would do this via instance Num T where (T t1) + (T t2) = T (t1 + t2) -- all other Num's methods = undefined I think we are good so far. Please, tell me if there are major concerns up to this point. Now let's suppose that I want to be able to multiply a T by an Int and that the result should

问题 Suppose I have a custom type wrapping an existing type, newtype T = T Int deriving Show and suppose I want to be able to add up T s, and that adding them up should result in adding the wrapped values up; I would do this via instance Num T where (T t1) + (T t2) = T (t1 + t2) -- all other Num's methods = undefined I think we are good so far. Please, tell me if there are major concerns up to this point. Now let's suppose that I want to be able to multiply a T by an Int and that the result should

问题 On Hackage I see that groupBy's implementation is this: groupBy :: (a -> a -> Bool) -> [a] -> [[a]] groupBy _ [] = [] groupBy eq (x:xs) = (x:ys) : groupBy eq zs where (ys,zs) = span (eq x) xs which means that the preticate eq holds between any two elements of each group . Examples: > difference_eq_1 = ((==1).) . flip (-) > first_isnt_newline = ((/= '\n').) . const > > Data.List.groupBy difference_eq_1 ([1..10] ++ [11,13..21]) [[1,2],[3,4],[5,6],[7,8],[9,10],[11],[13],[15],[17],[19],[21]] > >

问题 I am writing the function that can catch exceptions of the certain type only. def myFunc[A <: Exception]() { try { println("Hello world") // or something else } catch { case a: A => // warning: abstract type pattern A is unchecked since it is eliminated by erasure } } What is the corrent way to bypass jvm type erasure in such case? 回答1: You could use ClassTag like in this answer. But I'd prefer this approach: def myFunc(recover: PartialFunction[Throwable, Unit]): Unit = { try { println("Hello