Rust in a program

use "rust.qwer"server fn count_primes(n: int) -> map {    let started = now()    let r = primes(n)    merge(r, { ms: now() - started })}server fn collatz(n: int) -> map ! str {    let started = now()    let [number, length] = longest_collatz(n)?    { number, length, ms: now() - started }}component Lab() {    state n = 10000000    state primes_found = null    state chain = null    state problem = ""    <section.lab>        <label>Up to <input type="number" bind:value={n} min="2"/></label>        <div.buttons>            <button @click={() => { primes_found = count_primes(int(n)) }}>Count primes</button>            <button @click={() => {                let r = collatz(int(n))                problem = is_err(r) ? r.error : ""                chain = is_err(r) ? null : r            }}>Longest Collatz chain</button>        </div>        {primes_found != null && <p>            <b>{primes_found.count}</b> primes below {n}, the largest <b>{primes_found.largest}</b> ({primes_found.ms} ms)        </p>}        {chain != null && <p>            Below {n}, <b>{chain.number}</b> takes the most steps to reach 1: <b>{chain.length}</b> ({chain.ms} ms)        </p>}        {problem != "" && <p.problem>{problem}</p>}    </section>}let style = css`body { font: 16px/1.5 system-ui, sans-serif; max-width: 40rem; margin: 3rem auto; padding: 0 1rem; color: #1f2328; }input { font: inherit; width: 10rem; margin-left: .5rem; padding: .3rem .5rem; }.buttons { display: flex; gap: .5rem; margin: 1rem 0; }button { font: inherit; padding: .4rem .9rem; border-radius: 6px; border: 1px solid #d0d7de; background: #f6f8fa; cursor: pointer; }.problem { color: #cf222e; }`route GET / =    <html>        <head><meta charset="utf-8"/><title>Rust in Quillo</title><style>{style}</style></head>        <body><h1>Rust in Quillo</h1><Lab/></body>    </html>

//! Number work for rust.qwe, in Rust.//!//! Every top-level `pub fn` here is a function of the programs that//! `use "rust.qwer"`: Quillo builds this file (once per content) and loads it.use std::collections::HashMap;/// How many primes there are below `n`, and the largest of them.pub fn primes(n: i64) -> HashMap<String, i64> {    let n = n.clamp(0, 200_000_000) as usize;    let mut composite = vec![false; n];    let (mut count, mut largest) = (0, 0);    for i in 2..n {        if !composite[i] {            count += 1;            largest = i as i64;            let mut j = i * i;            while j < n {                composite[j] = true;                j += i;            }        }    }    HashMap::from([("count".to_string(), count), ("largest".to_string(), largest)])}/// The number below `n` whose Collatz sequence is longest, and its length.pub fn longest_collatz(n: i64) -> Result<Vec<i64>, String> {    if n < 2 || n > 50_000_000 {        return Err(format!("{} is out of range (2 to 50,000,000)", n));    }    let n = n as usize;    let mut steps = vec![0u32; n];    let (mut best, mut best_len) = (1, 1);    for start in 2..n {        let (mut x, mut len) = (start as u64, 0u32);        while x >= start as u64 {            x = if x % 2 == 0 { x / 2 } else { 3 * x + 1 };            len += 1;        }        steps[start] = len + steps[x as usize];        if steps[start] + 1 > best_len {            best = start;            best_len = steps[start] + 1;        }    }    Ok(vec![best as i64, best_len as i64])}