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I'm wondering if there is a language that supports programming in the following style that I think of as "data driven":

Imagine a language like C or Python except that it's possible to define a function whose input parameters are bound to particular variables. Then, whenever one of those input variables changes, the function is re-run.

Alternatively, the function might only ever be run when its output is needed, regardless of when its inputs are changed.

The first option is useful when things need to be kept up to date whenever something changes. The second option is useful when the computation is expensive, and you want to run it only when needed.

In my mind, this type of programming paradigm would require many stacks, perhaps one for each function that was defined in the above manner. This would allow those functions to be run in any order, and it would allow their execution to be occassionally blocked. Execution on one stack would be blocked anytime it needs the output of a function whose inputs are not yet ready.

This would be a single-threaded application. The runtime system would take care of switching from one stack to another in an appropriate manner. Deadlocks would be possible.

Martin
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  • This idea sounds similar to a spreadsheet. It has been argued elsewhere that spreadsheet programs are programming languages. – Ryan1729 Sep 23 '22 at 08:47
  • Yes, similar in the sense that dependencies are made explicit, and that a change can set off a chain reaction (of recalculations, in the case of a spreadsheet). In a C or Python program, such dependencies are just programmed with code, which can be tedious and error-prone. In the system I describe above, dependencies are just declared. – Martin Sep 23 '22 at 21:05

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