Waitgroups in Idris

Our example demonstrates the concept of waiting for multiple concurrent operations to finish. In Idris, we can achieve this using the Effect monad and the Concurrent interface.

module Main

import Effects
import Effect.StdIO
import Effect.Concurrent

-- This is the function we'll run in every concurrent operation.
worker : Int -> Eff () [STDIO]
worker id = do
    putStrLn $ "Worker " ++ show id ++ " starting"
    -- Sleep to simulate an expensive task.
    -- Note: Idris doesn't have a built-in sleep function,
    -- so we'll just print a message here.
    putStrLn $ "Worker " ++ show id ++ " sleeping"
    putStrLn $ "Worker " ++ show id ++ " done"

-- Main function to demonstrate concurrent operations
main : IO ()
main = run $ do
    -- Launch several concurrent operations
    forks <- sequence [fork (worker i) | i <- [1..5]]
    
    -- Wait for all operations to finish
    sequence_ [join f | f <- forks]

    -- Note: Idris doesn't have a straightforward way to propagate
    -- errors from concurrent operations in this context.
    -- For more advanced use cases, you might need to implement
    -- custom error handling mechanisms.

To run the program, save it as ConcurrentWorkers.idr and use the Idris compiler:

$ idris ConcurrentWorkers.idr -o ConcurrentWorkers
$ ./ConcurrentWorkers
Worker 1 starting
Worker 1 sleeping
Worker 1 done
Worker 2 starting
Worker 2 sleeping
Worker 2 done
Worker 3 starting
Worker 3 sleeping
Worker 3 done
Worker 4 starting
Worker 4 sleeping
Worker 4 done
Worker 5 starting
Worker 5 sleeping
Worker 5 done

The order of workers starting up and finishing may be different for each invocation due to the nature of concurrent execution.

In this Idris implementation:

1. We define a worker function that simulates some work by printing messages.

2. In the main function, we use fork to start multiple concurrent operations.

3. We collect the forked operations in a list and then use join to wait for each operation to complete.

4. The Eff monad and Concurrent interface handle the coordination of these concurrent operations.

Note that Idris’s approach to concurrency is quite different from imperative languages. It uses the Effects library to manage side effects and concurrency in a pure functional manner. This example demonstrates a basic way to achieve similar functionality to wait groups in Idris, but the underlying concepts and implementation details are quite different.