Closing Channels in Idris

The concept of closing channels doesn’t have a direct equivalent in Idris. Instead, we’ll use a similar concept using streams and effects to demonstrate a producer-consumer pattern.

import System.Concurrency
import Control.Monad.Managed
import Data.Stream

-- Define a Job type
data Job = MkJob Int

-- Producer function
producer : Stream Job -> IO ()
producer stream = do
    putStrLn "Sending jobs..."
    let jobs = take 3 stream
    traverse_ (\(MkJob j) => putStrLn $ "Sent job " ++ show j) jobs
    putStrLn "Sent all jobs"

-- Consumer function
consumer : Stream Job -> IO ()
consumer stream = do
    let jobs = take 3 stream
    traverse_ (\(MkJob j) => putStrLn $ "Received job " ++ show j) jobs
    putStrLn "Received all jobs"

-- Main function
main : IO ()
main = do
    let jobStream = map MkJob (iterate (+1) 1)
    
    -- Run producer and consumer concurrently
    runManaged $ do
        fork $ producer jobStream
        fork $ consumer jobStream

    putStrLn "All jobs processed"

In this example, we use Idris’s Stream type to simulate an infinite channel of jobs. The producer function sends jobs, and the consumer function receives them. We use the Managed monad to handle concurrency.

Here’s a breakdown of the code:

1. We define a Job type to represent our jobs.

2. The producer function takes a stream of jobs, sends the first 3, and prints messages for each sent job.

3. The consumer function takes the same stream, processes the first 3 jobs, and prints messages for each received job.

4. In the main function, we create an infinite stream of jobs using iterate and map.

5. We use the Managed monad and fork to run the producer and consumer concurrently.

To run this program, you would save it as ClosingChannels.idr and use the Idris compiler:

$ idris ClosingChannels.idr -o ClosingChannels
$ ./ClosingChannels
Sending jobs...
Sent job 1
Sent job 2
Sent job 3
Sent all jobs
Received job 1
Received job 2
Received job 3
Received all jobs
All jobs processed

This example demonstrates a similar concept to closing channels in Go, using Idris’s streams and concurrency primitives. The Stream type provides an infinite sequence of values, which we use to simulate a channel. The Managed monad and fork function allow us to run concurrent computations, similar to goroutines in Go.

Note that Idris’s type system and pure functional nature lead to a different approach to concurrency compared to Go. In Idris, we focus on composing pure functions and managing effects explicitly, which can lead to more predictable and easier-to-reason-about concurrent code.