kakoune-repl-send is a plugin that enables you to run an interpreter/a repl in the background and sent code to it from a buffer.
This code is then evaluated and the result is shown in another terminal window.
I use it a lot in development to explore function results or to do follow-up computations without having to run a long computation every time.
This version differs from kakoune-repl-bridge which also returns the output of the executed expression in the dquote register. The benefit of this plugin is that due to its simpler nature it works with more interpreters/repls (probably works with anything, you might even use another type of program that takes input from stdin).