This might go in a slightly different direction, but I would really love Fiber to define #to_proc allowing things like [1, 2, 3].each(&fiber).

Also note that in ANSI smalltalk (which has a rather common object model touby) a block closure is implementing the valuable protocol (objects that respond to #value and akin, smalltalk's #call), which would be something like the common ancestor for procs and fibers.

Konstantin