For "image" read, a runnable core file that can be updated (from within the program) and saved. Seriously. Forth and Smalltalk are two languages that are typi

For "image" read, a runnable core file that can be updated (from within the program) and saved. Seriously. Forth and Smalltalk are two languages that are typically "image" based. Because of that, the concept of a "program" might not make sense, because it's more of an operating environment. And even if you do buy the concept of a "program", each program is, in essence, a potential development environment (if the REPL is exposed---it can be sometimes be hidden or even modified). As such, a "program upgrade" is (in my opinion) insanely difficult to manage in such an environment, as the customer may have extended the program in an incompatible way with respect to the upgrade. Also, the concept of "source code" might not exist as we understand it (a human readable set of instructions the computer will carry out stored in a file or files). Forth will compile the code directly; Smalltalk (disclaimer: I have no experience with Smalltalk) might store the code you type somewhere, so it can be viewed and edited, but there's no guarantee it's a "file".