Sounds like the shift cable broke. Not likely the actual cable broke, but possibly became disconnected at one end or the other. Should be easy enough to check/repair. I'd suggest starting at the engine end since there's more vibration back there and you can access it just by popping the hatch. Have a friend move the lever and see if you can see the end of the cable moving. If it moves, you know it's connected/working at the shifter and the problem is at the engine end. If not, it's at the shift end.
Don
'01 22 Classic, 502/B1
And a bunch of other stuff
"If everything seems under control, you're just not going fast enough" - Mario Andretti