You evaulate code within your editor against the REPL, seeing the output in the same window you're writing in (perhaps in a different buffer).
The cycle is:
1. Write production code.
2. Write some dummy code in the same file (fake data, setup).
3. Evaluate that dummy code. See what happens.
4. Modify code until satisfied.
Your feedback loop is now single digit seconds, without context switching. It's extremely relaxing compared to the alternatives (rerunning tests, launching the program with flags, what have you).
The cycle is:
Your feedback loop is now single digit seconds, without context switching. It's extremely relaxing compared to the alternatives (rerunning tests, launching the program with flags, what have you).