[weikju]

You have files and editors for your files, eg emacs or vim or vscode.

Your editor is also directly connected to your running application and can compile individual functions or pieces of code to update the application without a full edit/compile/run/test loop. It happens way faster and more interactively while you code. You can directly inspect the running program and its data within that same framework and with the exact same tools and functions you use to code.

To answer another way, you don’t code your application in a REPL, like by line , but with all the tools you’d expect (editor or ide, git, etc) PLUS that live connection to your software.