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- -- A generic fifo module. See docs/lua-modules/fifo.md for use examples.
- local tr, ti = table.remove, table.insert
- -- Remove an element and pass it to k, together with a boolean indicating that
- -- this is the last element in the queue; if that returns a value, leave that
- -- pending at the top of the fifo.
- --
- -- If k returns nil, the fifo will be advanced. Moreover, k may return a
- -- second result, a boolean, indicating "phantasmic" nature of this element.
- -- If this boolean is true, then the fifo will advance again, passing the next
- -- value, if there is one, to k, or priming itself for immediate execution at
- -- the next call to queue.
- --
- -- If the queue is empty, do not invoke k but flag it to enable immediate
- -- execution at the next call to queue.
- --
- -- Returns 'true' if the queue contained at least one non-phantom entry,
- -- 'false' otherwise.
- local function dequeue(q,k)
- if #q > 0
- then
- local new, again = k(q[1], #q == 1)
- if new == nil
- then tr(q,1)
- if again then return dequeue(q, k) end -- note tail call
- else q[1] = new
- end
- return true
- else q._go = true ; return false
- end
- end
- -- Queue a on queue q and dequeue with `k` if the fifo had previously emptied.
- local function queue(q,a,k)
- ti(q,a)
- if k ~= nil and q._go then q._go = false; dequeue(q, k) end
- end
- -- return a table containing just the FIFO constructor
- return {
- ['new'] = function()
- return { ['_go'] = true ; ['queue'] = queue ; ['dequeue'] = dequeue }
- end
- }
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