Definitely. Dyalog APL has support for source files, too, but I didn't want to overcomplicate things. The way that it saves environments (i.e. to a binary file

Definitely. Dyalog APL has support for source files, too, but I didn't want to overcomplicate things. The way that it saves environments (i.e. to a binary file or to a source file) is tangential to the point: that it has the ability to save the environment at all. REPLs go best with languages that can save their live environments, so that you don't have to worry about getting your work back out of the REPL environment. If your language can't save its environment, you need some other way to improve the REPL-to-source workflow.