a.mill

// <- for send and receive

import mill.time
import mill.conc.chan
import mill.conc.thread

sub withTimeout[R](timeout: time.Duration, s: () => R): R {
    let resultChan = chan.make[R]()
    thread.spawn(sub(): () { resultChan <- s() })
    select {
    case let result = <-resultChan => result
    case let _ = <-time.after(timeout) => throw(timeoutError)
    }
}

b.mill

// chan.send and chan.recv for send and receive

import mill.time
import mill.conc.chan
import mill.conc.thread

sub withTimeout[R](timeout: time.Duration, s: () => R): R {
    let resultChan = chan.make[R]()
    thread.spawn(sub(): () { chan.send(resultChan, s()) })
    select {
    case let result = chan.recv(resultChan) => result
    case let _ = chan.recv(time.after(timeout)) => throw(timeoutError)
    }
}

c.mill

// always-in-scope (unless shadowed) send and recv for send and receive

import mill.time
import mill.conc.chan
import mill.conc.thread

sub withTimeout[R](timeout: time.Duration, s: () => R): R {
    let resultChan = chan.make[R]()
    thread.spawn(sub(): () { send(resultChan, s()) })
    select {
    case let result = recv(resultChan) => result
    case let _ = recv(time.after(timeout)) => throw(timeoutError)
    }
}