'let :=' for immediate evaluation in assignment.  Does this work
for included files?

Default parameters, ie:
  goal foo (name, release = true) = ...
You might only allow defaults to be added to the end, or you
might allow goals to be called with labelled parameters.

Fix: You must use 'all ()' on the command line.

"Quiet" code.  Generally {CODE} sections in user files should be
echos, and those in stdlib should run silently (except if debugging).
Maybe we should have a quiet keyword to indicate this?