functional-programming

问题 I recently stumbled on the concept of a Kleisli and every tutorial/link/reference that I read motivates the use of Kleisli via the following constructs: Composing functions that return monads : f: a -> m[b] with g: b -> m[c] - I think the very definition of a monad already captures this case - do/bind/for/flatMap do that. One needn't lean on the Kleisli construct to achieve this. So this cannot be the "primary" use case of a Kleisli IMO. Inserting configuration : This one states that if

问题 I am really trying to learn a bit of ELM, but my mind collapse at the query parse, my idea was to create a function to get a query string value by name something like: given an query string ?name=Neuber a function like this getParam "name" that would return Neuber But its failing at most basic example, it doesn't even compile page comes from here routeParser comes from here module Main exposing (..) -- import Url.Parser exposing (Parser, (</>), (<?>), oneOf, s) import Url.Parser.Query

问题 I am really trying to learn a bit of ELM, but my mind collapse at the query parse, my idea was to create a function to get a query string value by name something like: given an query string ?name=Neuber a function like this getParam "name" that would return Neuber But its failing at most basic example, it doesn't even compile page comes from here routeParser comes from here module Main exposing (..) -- import Url.Parser exposing (Parser, (</>), (<?>), oneOf, s) import Url.Parser.Query

问题 I am really trying to learn a bit of ELM, but my mind collapse at the query parse, my idea was to create a function to get a query string value by name something like: given an query string ?name=Neuber a function like this getParam "name" that would return Neuber But its failing at most basic example, it doesn't even compile page comes from here routeParser comes from here module Main exposing (..) -- import Url.Parser exposing (Parser, (</>), (<?>), oneOf, s) import Url.Parser.Query

问题 I've been digging into FP and everything that surrounds it, and I found the concept of kind projector written somewhere, without details nor explanations. The only thing I found was this github project, and I'm starting to think if it was referring to this particular project, or to some generic concept in FP? So, what is a kind projector? Why is it useful? (if possible, can you provide examples, resources, etc?) 回答1: This is indeed just a slightly awkward name for the specific plugin for the

问题 How is most "pure" way to manipulate DOM in script written in "functional" way. For example if I simply need to change element width should I use typical syntax like: document.querySelector(".class").style.width = ... or write dedicated function, like: function resize(el, w) { return el.style.width = w; } resize(document.querySelector(".class", 100)); I think, I understand general idea of functional programming but all examples I encountered are focused on manipulating numbers or strings.

问题 I am trying to learn functional programming and Scala, so I'm reading the "Functional Programming in Scala" by Chiusano and Bjarnason. I' m having trouble understanding what fold left and fold right methods do in case of a list. I've looked around here but I haven't find something beginner friendly. So the code provided by the book is: def foldRight[A,B](as: List[A], z: B)(f: (A, B) => B): B = as match { case Nil => z case Cons(h, t) => f(h, foldRight(t, z)(f)) } def foldLeft[A,B](l: List[A],

问题 So I have the generic method set up consisting of: A parameter of type T A List of T's (which will be the data set that I will be looking at) A function from T to double (This function will be used to take a property from each data element. So basically the property is used to compute the and return standard deviation.) For example the List(7.63, 3.87, 1.59, 8.26, 5.11, 0.65, 7.88) should return 3.100496888 That last bullet is confusing me and I'm not sure how to put it in the form of

问题 rlang::invoke() is now soft-deprecated, purrr::invoke() retired. These days, what is the tidy approach to programmatically calling a function with a list of arguments? 回答1: tldr; Use exec instead of invoke ; use map2 plus exec instead of invoke_map . Example for invoke With retired invoke set.seed(2020) invoke(rnorm, list(mean = 1, sd = 2), n = 10) #[1] 1.7539442 1.6030967 -1.1960463 -1.2608118 -4.5930686 2.4411470 #[7] 2.8782420 0.5412445 4.5182627 1.2347336 With exec set.seed(2020) exec

问题 I am a beginner in Racket and I am trying to updare a hash table using hash-update! where the value is a mutable set. Below are the code lines: (hash-update! hash key (curryr set-add! new_val) (mutable-set 1)) However I receive an error expected: set? given: #<void> argument position: 1st other arguments...: x: 2 where I tried 2 as the new_val Any suggestions ? 回答1: This is because the updater is supposed to be a function that takes a value as input and produces a new value output. Since the