To add on to what others have said, a good repl lets you point it at at a minimum of a file and load its contents into active state (so if you want access to a

To add on to what others have said, a good repl lets you point it at at a minimum of a file and load its contents into active state (so if you want access to a bunch of functions you load that file based on the command of the language you are in). You can then do the one lines you are talking about, but you could also update the file if you find you want to tweak a function and usually highlight and ctrl+enter to re-evaluate that one function, updating its state in the live environment. This way instead of recompiling the entire system you recompile that one function and anything using it now points to the new version. F# actually has this and while it probably is not as powerful as Slime with CL it can give an idea of the power you are missing (and F#'s has gotten some nice improvements in the script side of .fsx files such as being able to add nuget files with a line in the script in newer versions).