HaskellでGoぽく定期実行

chan2.go

package main

import (
	"fmt"
	"time"
)

func main() {
	fmt.Println("Starting...")
	ch := time.After(3 * time.Second)
	<-ch
	fmt.Println("Started")
	ch = time.Tick(3 * time.Second)
	for _ = range ch {
		fmt.Println("3")
	}
}

chan2.hs

import Control.Concurrent (forkIO, threadDelay)
import Control.Concurrent.Chan (Chan, newChan, readChan, writeChan)
import Control.Monad (forever)

delay :: Int -> IO ()
delay = threadDelay . (* 1000000)

after :: Int -> IO (Chan ())
after time = do
    ch <- newChan
    _ <- forkIO $ delay time >> writeChan ch ()
    return ch

tick :: Int -> IO (Chan ())
tick time = do
    ch <- newChan
    _ <- forkIO $ forever $ delay time >> writeChan ch ()
    return ch
    
main :: IO ()
main = do
    putStrLn "Starting..."
    after 3 >>= readChan
    putStrLn "Started"
    ch' <- tick 3
    forever $ readChan ch' >> putStrLn "3"