An unavailable value is a special payload to a reactive system unifying handling of errors and asynchrony under a common mechanism responding to “design incompletion for any reason”. I named a special reactive payload as an “unavailable value” indicating that the design was incomplete either as a result of depending on pending I/O or else on a design/syntax error in the system.
My first 2024 simplistic version of this simply repurposed the JavaScript undefined value as a special reactive payload that would short-circuit behaviour of any computed and cull the action of any effect that was geared through it.
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