Simple example of coroutine based recursive searchPath

coro_searchPath.lua

ax=hs.axuielement
dockAX = ax.applicationElement(hs.application("Dock"))

ids={"mc","mc.display","mc.spaces"}

scf={}
for i,id in ipairs(ids) do
   table.insert(scf,ax.searchCriteriaFunction(
		   {{attribute="AXRole",      value="AXGroup"},
		    {attribute="AXIdentifier",value=id}}))
end

function searchPath(start,searchCriteriaFunctions,callback) 
   local co=coroutine.create(function (myco)
	 local searchResume = function (msg,results,cnt)
	    coroutine.resume(myco,results,cnt)
	 end
	 local elem={start} 
	 for _,search in ipairs(searchCriteriaFunctions) do
	    for _,el in ipairs(elem) do -- search all in parallel
	       el:elementSearch(searchResume, search, {depth=1})
	    end
	    local num=#elem
	    elem={}
	    if num==0 then break end
	    for _=1,num do -- wait for all searches to return
	       res,cnt=coroutine.yield()
	       for _,r in ipairs(res) do
		  table.insert(elem,r)
	       end
	    end
	 end
	 callback(elem)
   end)
   coroutine.resume(co,co)
end

-- Invoke Mission Control before running the Search
hs.timer.doAfter(2,function()
		    searchPath(dockAX,scf,
			       function (els)
				  print('Results: ')
				  for i,v in ipairs(els) do
				     print(v,v.AXIdentifier)
				  end
		    end)
end)