等差数列

ap.d

import std.stdio;

int f(int a, int d, int n){
  return a + d * (n - 1);
}

int sumf(int n, int function(int) fx){
  return n * (fx(1) + fx(n)) / 2;
}

void main(){
  auto fn = ((int n) => f(1, 1, n));
  sumf(10, fn).writeln;
}