Try ReactiveML

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ReactiveML is a programming language similar to OCaml extended with the synchronous reactive model. It is dedicated to the implementation of interactive systems as found in graphical user interfaces, video games and simulation problems.

For example, the file planet.rml contains a simple implementation of the n-body problem:

lessons/planets.rml

You can add ten new planets moving in parallel by typing the following line or simply by clicking on it:

#exec (for i = 1 to 10 dopar run planet done);;

You can stop the simulation with:

emit quit;;