confusing error message on (4)

[jbclements]

When I run this program (or many other syntactically invalid programs):

#lang pie

(4)

... I get the error message

?: expected more terms starting with rand
  parsing context: 
   while parsing application in: (4)

I don't understand what 'rand' has to do with this situation. Could this error message be improved?

Thanks!

[david-christiansen]

New message:

?: expected more terms starting with first argument
  parsing context: 
   while parsing function application in: (4)

Thanks!