In a number of languages with a number of editors / editor plugins, with a code file open I can easily keep open in parallel a REPL window/tab that has the code

In a number of languages with a number of editors / editor plugins, with a code file open I can easily keep open in parallel a REPL window/tab that has the code file (and libs/pkgs/modules that it imports) loaded in interpreted mode and can reload either on save or if that isn't hooked up, certainly by a repl command like `:reload` in GHCi which I use in SublimeHaskell. Marvellous "live-coding" experience of sorts. Works particular well when writing pure functions (same in = same out, every time, no side-effects etc) and in a language where quickly defining some temp vars for passing some random test arguments in a swift non-verbose manner is a total non-issue