Toggle Display Units

Hey everyone.

I'm trying to create a shortcut to toggle between display unit types: US Ft with Decimal inches and Metric Millimeters (since I switch between the two so often). I know there's a script out there with a floater that has buttons to switch between these but I was hoping to just have it in a shortcut.

This seems like it should be the simplest thing in the world but... I'm pretty noob and obviously missing something here. Here's what I have:

macroScript ToggleDisplayUnits
category:"MyTools T"
ButtonText:"ToggleDisplayUnits"
Tooltip:"Toggle Display Units"

(
if units.displayType=#US units.USType=#Ft_Dec_In then
(
units.displayType=#Metric units.metricType=#Millimeters
)
else
(
units.displayType=#US units.USType=#Ft_Dec_In
)
)

The error it gives me is:

-- No "=" function for (#us (prop USType Global:units))

Again, I'm a complete newb -_- Any tips or pointers would be greatly appreciated!