REPL-Based Development and Feedback Loops
In recent years we have heard a lot about feedback loops in software development. REPL-Based development gives us additional levels of feedback loop.
Some examples of feedback loops, working roughly from fine-grained to coarse-grained loops (the precise order will be different for different processes), are:
Run Automatic Test Suite Get continuous feedback from test code.
Pair Programming Get continuous feedback from other developers.
Stand-ups Every day or so, report on what we are doing and what's holding us up.
Software Releases Every so often, release a new version of software; this allows us to get feedback from customers.
Retrospectives Every week or two, reflect on what's working and what's not working.
Most lists of feedback loops start with automatic tests, but can we get more fine-grained?
We can, with REPL-Based development.
For a detailed explanation of what REPL-based development is, see my REPL-based development article. One of the points I make there is that REPL-based development gives us the following feedback loops:
Explore Using a REPL Window We make use of a REPL window for simple exploration.
Evaluate Forms from Editor Windows We build up a program bit by bit in editor windows, and we repeatedly send new and modified forms to the REPL process.
Save to File We save our changes to file, and we load and run larger chunks of code in various ways.
Reload the REPL We regularly reload from scratch.
The list of REPL-based feedback loops almost dovetails with our first list of feedback loops — “almost” because the automatic test level is lower than the reload the REPL level. So we end up with:
Explore Using a REPL Window
Evaluate Forms from Editor Windows
Save to File
Run Automatic Test Suite
Reload the REPL
OK, maybe not deep, but probably worth writing down.