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  • deref on some IDerefs can block.
    • futures
    • promises
  • problem - If you can't accept blocking indefinitely you have no alternative
  • some reference type might not yet have a value
    • futures
    • promises
    • delays
  • problem - if you need to make a decision based upon whether or not such a reference has a value you can't, without forcing/blocking

Possible solutions

  • categorize references that can block
    • e.g. IMightBlock
  • offer a deref with timeout
    • e.g. (deref blocking-ref timeout timeout-val)
  • categorize references that might not yet have a value
    • e.g. IMightNotHaveAValue
  • offer a query fn for that
    • (has-value? aref)


  • which (if any) of these make sense for other refs?
    • timeout seems really confusing for non-blocking
    • has-value? could be trivially true for other refs
      • but causes paranoia?



  • I want to know if a potentially blocking deref has a value
    • future-done? for Future
    • (.hasValue foo) for Promise