Play back at half-time REAPER script

JRB_PlaybackHalftime.lua

--[[
  toggle transport playrate between 0.5 and 1.0;

  sets master transport playback rate to 0.5
  if currently at 0.5, sets to 1.0

  by Jon Bash (@jonbash, www.jonbash.com)
]]--

playrate = reaper.Master_GetPlayRateAtTime(0)

function playback_halftime()
  if (playrate == 0.5) then
    -- reaper.Master_NormalizePlayRate(number playrate, boolean isnormalized)
    -- reaper.Master_NormalizePlayRate(1, false)
    -- reaper.CSurf_OnPlayRateChange(number playrate)
    reaper.CSurf_OnPlayRateChange(1)
  else
    reaper.CSurf_OnPlayRateChange(0.5)
  end
end

function main()
  playback_halftime()
end

main()