How does that really work? Because at the end of the day, to build your program, you need to have code in a source file of disk Not necessarily in the way you

How does that really work? Because at the end of the day, to build your program, you need to have code in a source file of disk Not necessarily in the way you'd imagine. In Smalltalk, there is what amounts to a transaction log of your code changes, which you can replay. There is also an operation analogous to a database "checkpoint" where you save the whole memory image. In most production environments, there is a 3rd mechanism which also tracks and saves the configuration in a database, which also serves as part of a build/deployment mechanism. Code in the REPL is not persistent In Smalltalk, all code executed in one of the REPL-like things is recorded on the transaction log of your code changes. I am guessing you actually mean, that development was REPL supported, and that you used the repl to test your code, and help you design your code In many Smalltalk environments, there are REPL-like things everywhere, including the many of the fields/panes of the debugger, and seasoned Smalltalkers would pretty much write the system in the debugger.