Do not tackle the bigger "abstractions around visibility, delay, blocking" etc. issue. This is a minimal fix:

• print code already deals with future as a special case

• should special-case promise as well

• make a definterface IPromiseImpl that you can switch on

  • right above promise in core.clj

  • has a method that gets you what you need to ask "has-value?"

• in print code

  • if has value, show it, if not, show :not-delivered

• make sure to fix print code in both core_print and pprint