test2.lua

local log = {}
local _f = {}
_f["swing"] = robot.swing
_f["sleep"] = function() os.sleep(.4) return true end

local function run(f)
    table.insert(log, os.clock().." "..f)
    if _f[f] then
        table.insert(log, os.clock().." "..f.." end")
    else
        table.insert(log, os.clock().." "..f.." end")
    end
end

run("swing")
run("sleep")

print(textutils.serialise(log))