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operator	is referent
	Related Syntax

Summary

Boolean Returns true if the stream is attached to a referent and false otherwise. Replacing is with isnt will reverse the results.

Syntax

  stream? stream-name  indexer? (is | isnt) referent

Tests whether the specified stream is attached to a referent.

Note that if a stream is bound to a previously defined referent and then discarded, that referent still exists, but is no longer attached.