partial-application

Given some function f(x1,x2,x3,..,xN) it is often useful to apply it partially in several places. For example, for N=3 we could define g(x)=f(1,x,3). However, the standard partial application in Haskell does not work this way and only allows us to partially apply a function by fixing its first arguments (because all functions actually only take one argument). Is there any simple way to do something like this: g = f _ 2 _ g 1 3 with output the value of f 1 2 3 ? Of course we could do a lambda-function g=(\x1 x3 -> f x1 2 x3) but I find this quite unreadable. For example, in Mathematica it works

I'm a bit shaky on the rules as to when you need a _ after a method to use it as a function. For example, why is there a difference between Foo 's and Nil 's :: in the following? def square(n: Int) = n * n object Foo { def ::(f: Int => Int) = f(42) } // ... scala> Foo.::(square) res2: Int = 1764 scala> Nil.::(square) <console>:6: error: missing arguments for method square in object $iw; follow this method with `_' if you want to treat it as a partially applied function Nil.::(square) ^ scala> Nil.::(square _) res3: List[(Int) => Int] = List(<function1>) When you omit all parameters in a

I'd like to have a function BindFirst that binds the first argument of a function without me having to explicitly know/state the arity of the function by using std::placeholders. I'd like the client code to look something like that. #include <functional> #include <iostream> void print2(int a, int b) { std::cout << a << std::endl; std::cout << b << std::endl; } void print3(int a, int b, int c) { std::cout << a << std::endl; std::cout << b << std::endl; std::cout << c << std::endl; } int main() { auto f = BindFirst(print2, 1); // std::bind(print2, 1, std::placeholders::_1); auto g = BindFirst

Suppose I have a function in R that takes multiple arguments, and I'd like to reduce it to a function of fewer arguments by setting some of the arguments to pre-specified values. I'm trying to figure out what is the best way to do this is in R. For example, suppose I have a function f <- function(a,b,c,d){a+b+c+d} I'd like to create or find a function partial that would do the following partial <- function(f, ...){ #fill in code here } new_f <- partial(f, a=1, c= 2) new_f would be a function of b and d and would return 1+b+2+d In python I would do from functools import partial def f(a,b,c,d):