Atomic Counters in Idris

Here’s the translation of the atomic counters example from Go to Idris:

import System.Concurrency
import Data.IORef

main : IO ()
main = do
    -- We'll use an IORef to represent our counter
    ops <- newIORef 0

    -- We'll use a MVar as a simple way to wait for all threads to finish
    done <- newEmptyMVar

    -- We'll start 50 threads that each increment the counter exactly 1000 times
    let numThreads = 50
    let incrementsPerThread = 1000

    -- Start the threads
    for_ [1..numThreads] $ \_ -> do
        fork $ do
            for_ [1..incrementsPerThread] $ \_ -> do
                modifyIORef' ops (+1)
            putMVar done ()

    -- Wait for all threads to finish
    for_ [1..numThreads] $ \_ -> takeMVar done

    -- Read the final value of the counter
    finalOps <- readIORef ops
    putStrLn $ "ops: " ++ show finalOps

This Idris code demonstrates a similar concept to the Go example of atomic counters, but with some differences due to the language’s features and idioms:

1. We use IORef instead of atomic.Uint64. IORef in Idris is not inherently atomic, but in this single-threaded runtime, it serves a similar purpose.

2. Instead of sync.WaitGroup, we use an MVar as a simple synchronization mechanism. We create an empty MVar for each thread and have the main thread wait on all of them.

3. We use fork to create new threads, which is similar to goroutines in Go.

4. The modifyIORef' function is used to increment the counter. This is not atomic in the same way as Go’s atomic operations, but it serves a similar purpose in this context.

5. We use for_ from the Idris standard library to create loops, both for creating threads and for the increments within each thread.

6. At the end, we read the final value of the counter using readIORef and print it.

To run this program, you would save it in a file with a .idr extension, for example AtomicCounters.idr, and then use the Idris compiler:

$ idris AtomicCounters.idr -o atomic-counters
$ ./atomic-counters
ops: 50000

Note that due to Idris’s single-threaded runtime, this program doesn’t actually run concurrently. In a real-world scenario with true concurrency, you would need to use more sophisticated synchronization mechanisms to ensure thread safety.