functional-programming

问题 I'm learning javascript FP by reading DrBoolean's book. I searched around for functional programming library. I found Ramda and Folktale. Both claim to be functional programming library. But they are so different: Ramda seems to contain utility functions for dealing with list: map, reduce, filter and pure functions: curry, compose. It doesn't contain anything to deal with monad, functor. Folktale however doesn't contain any utility for list or functions. It seems to implement the some

问题 Horner's rule is used to simplify the process of evaluating a polynomial at specific variable values. https://rosettacode.org/wiki/Horner%27s_rule_for_polynomial_evaluation#Standard_ML I've easily applied the method using SML, to a one variable polynomial, represented as an int list: fun horner coeffList x = foldr (fn (a, b) => a + b * x) (0.0) coeffList This works fine. We can then call it using: - val test = horner [1.0, 2.0, 3.0] 2.0; > val test = 17.0 : real Where [1.0, 2.0, 3.0] is the

问题 A common use case in R (at least for me) is identifying observations in a data frame that have some characteristic that depends on the values in some subset of other observations. To make this more concerete, suppose I have a number of workers (indexed by WorkerId) that have an associated "Iteration": raw <- data.frame(WorkerId=c(1,1,1,1,2,2,2,2,3,3,3,3), Iteration = c(1,2,3,4,1,2,3,4,1,2,3,4)) and I want to eventually subset the data frame to exclude the "last" iteration (by creating a

问题 I know the Function class can be passed as a parameter to another function, like this: void doSomething(Function f) { f(123); } But is there a way to constrain the arguments and the return type of the function parameter? For instance, in this case f is being invoked directly on an integer, but what if it was a function accepting a different type? I tried passing it as a Function<Integer> , but Function is not a parametric type. Is there any other way to specify the signature of the function

问题 I am having a tough time understanding why the Scala compiler is unhappy about this function definition: def trimNonWordCharacters[T <: Iterable[String]](items: T): T = items map { _.replaceAll("\\W", "") } Here is the REPL output: scala> def trimNonWordCharacters[T <: Iterable[String]](items: T): T = items map { _.replaceAll("\\W", "") } <console>:5: error: type mismatch; found : Iterable[java.lang.String] required: T def trimNonWordCharacters[T <: Iterable[String]](items: T): T = items map

问题 I have a map of form shown below: Map = #{#{country=>"India"} => #{rank => 1}}. I am trying to match it as follows: 1. #{Key := V} = Map. OR 2. #{#{country := Country} := #{rank := Rank}} = Map. But its not working for me. Any help as to how it can be done? 回答1: When matching key-value associations from maps the key expression must be an expression with literals or bound variables, see the documentation of maps (section Maps in Patterns ). The problem with a match expression like: #{Key := V}

问题 I am currently trying out things in Scala, trying to get accustomed to functional programming as well as leaning a new language again (it's been a while since last time). Now given a list of strings if I want to merge them into one long string (e.g. "scala", "is", "fun" => "scalaisfun" ) I figured one way to do it would be to do a foldRight and apply concatenation on the respective elements. Another way, admittedly much simpler, is to call mkString . I checked on github but couldn't really

问题 Looking at the source for Ramda.js, specifically at the "lift" function. lift liftN Here's the given example: var madd3 = R.lift(R.curry((a, b, c) => a + b + c)); madd3([1,2,3], [1,2,3], [1]); //=> [3, 4, 5, 4, 5, 6, 5, 6, 7] So the first number of the result is easy, a , b , and c , are all the first elements of each array. The second one isn't as easy for me to understand. Are the arguments the second value of each array (2, 2, undefined) or is it the second value of the first array and the

问题 Looking at the source for Ramda.js, specifically at the "lift" function. lift liftN Here's the given example: var madd3 = R.lift(R.curry((a, b, c) => a + b + c)); madd3([1,2,3], [1,2,3], [1]); //=> [3, 4, 5, 4, 5, 6, 5, 6, 7] So the first number of the result is easy, a , b , and c , are all the first elements of each array. The second one isn't as easy for me to understand. Are the arguments the second value of each array (2, 2, undefined) or is it the second value of the first array and the

问题 I'm very new to JS, I've tried code below : function isBigEnough(element, index, array, threshold) { return (element >= threshold); } [1, 2, 3].every(isBigEnough(threshold=0) I thought it doesn't work because prototype (in Array.prototype.filter() ) does not contain threshold, so it is types mismatch, but we can't define like this : isBiggerThenZero = isBigEnough(threshold=0) so is there nice workaround for this case ? 回答1: When you do [1, 2, 3].every(isBigEnough(0)) . It: Calls isBigEnough