我已经将一段 Rust 代码示例翻译成 Clojure。
Rust(命令式和函数式):
注意:这里将命令式和函数式代码放在一起以增加清晰度。在测试中,我会分别运行它们。
// The `AdditiveIterator` trait adds the `sum` method to iterators
use std::iter::AdditiveIterator;
use std::iter;
fn main() {
println!("Find the sum of all the squared odd numbers under 1000");
let upper = 1000u;
// Imperative approach
// Declare accumulator variable
let mut acc = 0;
// Iterate: 0, 1, 2, ... to infinity
for n in iter::count(0u, 1) {
// Square the number
let n_squared = n * n;
if n_squared >= upper {
// Break loop if exceeded the upper limit
break;
} else if is_odd(n_squared) {
// Accumulate value, if it's odd
acc += n_squared;
}
}
println!("imperative style: {}", acc);
// Functional approach
let sum_of_squared_odd_numbers =
// All natural numbers
iter::count(0u, 1).
// Squared
map(|n| n * n).
// Below upper limit
take_while(|&n| n < upper).
// That are odd
filter(|n| is_odd(*n)).
// Sum them
sum();
println!("functional style: {}", sum_of_squared_odd_numbers);
}
fn is_odd(n: uint) -> bool {
n % 2 == 1
}
Rust(命令式)时间:
~/projects/rust_proj $> time ./hof_imperative
Find the sum of all the squared odd numbers under 1000
imperative style: 5456
real 0m0.006s
user 0m0.001s
sys 0m0.004s
~/projects/rust_proj $> time ./hof_imperative
Find the sum of all the squared odd numbers under 1000
imperative style: 5456
real 0m0.004s
user 0m0.000s
sys 0m0.004s
~/projects/rust_proj $> time ./hof_imperative
Find the sum of all the squared odd numbers under 1000
imperative style: 5456
real 0m0.005s
user 0m0.004s
sys 0m0.001s
Rust(函数式)时间:
~/projects/rust_proj $> time ./hof
Find the sum of all the squared odd numbers under 1000
functional style: 5456
real 0m0.007s
user 0m0.001s
sys 0m0.004s
~/projects/rust_proj $> time ./hof
Find the sum of all the squared odd numbers under 1000
functional style: 5456
real 0m0.007s
user 0m0.007s
sys 0m0.000s
~/projects/rust_proj $> time ./hof
Find the sum of all the squared odd numbers under 1000
functional style: 5456
real 0m0.007s
user 0m0.004s
sys 0m0.003s
Clojure:
(defn sum-square-less-1000 []
"Find the sum of all the squared odd numbers under 1000
"
(->> (iterate inc 0)
(map (fn [n] (* n n)))
(take-while (partial > 1000))
(filter odd?)
(reduce +)))
Clojure时间:
user> (time (sum-square-less-1000))
"Elapsed time: 0.443562 msecs"
5456
user> (time (sum-square-less-1000))
"Elapsed time: 0.201981 msecs"
5456
user> (time (sum-square-less-1000))
"Elapsed time: 0.4752 msecs"
5456
问题:
(reduce +)
和(apply +)
在Clojure中有什么区别?- 这段Clojure代码是否符合惯用方式?
- 我能得出结论:速度:Clojure > Rust命令式 > Rust函数式吗?Clojure在性能方面真的让我感到惊讶。
time
shell 工具包含整个程序的执行过程,不仅仅是直接计算(与 Clojure 的time
不同),因此不适用于比较运行时间非常短的程序,例如time true
(什么也不做)在我的电脑上的运行时间范围从 0.002 秒到 0.006 秒。 - huon