> Even if it were somehow to ignore api calls that say, modify your filesystem, how would the IDE 'know' about that api. Will someone have to manually go through all the apis in existence and make a list of which ones to emulate and which ones to not? That doesn't seem practical.
Why do Light Table need to emulate something? People have been executing code in REPL since forever, Light Table instant feedback seems like an extension to the REPL concept, with an ability to substitute all variables visually in-place. I can't see why it should be any different.
Because when you execute code in a REPL you choose when to do so, presumably because you understand the side effects. The IDE doesn't but has to execute the code anyway to give you the feedback. This might be useful for pure functions but you'd need some kind of integrated mocking functionality for impure code.
Why do Light Table need to emulate something? People have been executing code in REPL since forever, Light Table instant feedback seems like an extension to the REPL concept, with an ability to substitute all variables visually in-place. I can't see why it should be any different.