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Read from a Queue repeatedly until it is closed.

When an element is received, call action and recurse if it returns True. When no element is available, evaluate na and recurse if it returns True.

Read from a Queue repeatedly until it is closed.

When an element is received, call action and recurse.

Read from a Queue and convert the result to Maybe, returning Nothing if there is no element available or the queue has been closed.

Abstracts queues like TBQueue.

For documentation on the constructors, see the module Polysemy.Conc.Data.Queue.

import Polysemy.Conc (Queue, QueueResult)
import Polysemy.Conc.Effect.Queue as Queue

prog :: Member (Queue Int) r => Sem r (QueueResult Int)
prog = do
  Queue.write 5
  Queue.write 10
  Queue.read >>= \case
    QueueResult.Success i -> fmap (i +) <$> Queue.read
    r -> pure r