You might want to have a look at Matt Paras’s config. He’s been developping the plugin system using steel, his own scheme interpreter in rust.
To send things to the repl, it uses eval-buffer from the helix-ext.scm file.
The integration and customizability is for sure not that of Emacs yet, but with the plugin system soon to be merged, we can hope to have a proper REPL and Parinfer implementation!
https://github.com/mattwparas/helix-config
