Ep 102: REPLify!

Each week, we discuss a different topic about Clojure and functional programming.

If you have a question or topic you'd like us to discuss, tweet @clojuredesign, send an email to feedback@clojuredesign.club, or join the #clojuredesign-podcast channel on the Clojurians Slack.

This week, the topic is: "using the REPL to explore". We find ourselves in a murky situation, so we go to our REPL-connected editor to shine some light on the details.

Our discussion includes:

• Diving into the world of Sportify!
• How do you get started when diving into a new automation problem?
• The exact workflow we use for exploring existing systems.
• What is a "streaming specification"?
• How can the REPL help us explore?
• What does it mean for an editor to be REPL-connected?
• What is a "fiddle file"? What is a "fiddle workflow"?
• The first things we do when we start a brand new project.
• Switching from Leiningen to Clojure tools.
• Options for where to put your fiddle files.
• How to run a single Clojure file.
• What goes in our very first fiddle file? How do we build it up?
• How we handle configuration when we're fiddling.
• How to get connected and explore a database from a fiddle.
• Tips and tricks for exploring a database from a fiddle.
• Using defs to help work with live data.
• How long does it take to get started?

Selected quotes:

• "We often want to see highlights more than we want to see the game."

• "Like so many things with interns, there is really low supervision, so no one's really worried about how we get it done."

• "Having something done is better than not, so the bar is 0."

• "It sounds like a natural integration with an asynchronous message queue called 'Outlook'."

• "I like to call it 'streaming specification'. I'm not going to tell you everything. I'm coming up with this off the top my head."

• "We call them situated problems. They're problems that are set in the real world, so you need to know about all the things in the real world. It's a learning problem."

• "You say, 'the things we can't control.' I think of it as, 'the things that are foisted upon us!'"

• "We're going to find a way to use Clojure to solve this problem. I bet you didn't see that coming!"

• "The first thing I usually do is go for the completely correct and entirely comprehensive documentation that describes all of the different use cases that I might need, and in fact, has a sample code." (Ha! If only!)

• "It can be said that programming is debugging an empty file." "The first bug is my application does nothing!"

• "You want to get to your first rewrite as fast as possible, so write the messy version first. Then you can learn what you want the next version to be—even if the next version is also messy. The sooner you learn the better."

• "I'm starting to build up little pieces to help me explore."

• "We're going to figure it out interactively, using the REPL. We're getting our bearings."

• "Get in the code right away—hitting an external service as soon as possible—so we can begin to learn, so that we're solving the right problem instead of some problem of our imagination."

• "Once it's Clojure data structures, the whole world of Clojure opens up. All the power of mixing and matching and analyzing that data is open to you."

• "We're getting into the real thing. We're getting real data, real code. This is going to begin to grow up into something, but for now, we just want to see what's there—begin to explore—get some working code so that we can."

• "It's hard to imagine the workflow, because it's not a workflow that you do in other languages. If you haven't done this before, it's hard to just imagine it."

• "It's not just REPL first, but REPL-connected editor first, and there's a distinction."

Clojure command line

If you are unfamilar with the Clojure command line, check out the Deps and CLI Guide. You can set up global aliases in $HOME/.clojure/deps.edn. For example, this is one Christoph uses:

{:aliases
 {:nrepl {:extra-deps {nrepl/nrepl {:mvn/version "RELEASE"}
                       cider/piggieback {:mvn/version "RELEASE"}}
          :jvm-opts ["-server" "-XX:MaxMetaspaceSize=256m" "-Xmx1280m"]
          :main-opts ["-m" "nrepl.cmdline"]}}}

Run it with:

clojure -M:nrepl

You can see more examples in Nate's dotfiles and in Sean Corfield's dot-clojure project.

Links:

• Ep 014: Fiddle with the REPL
• Use #_ to ignore the next form
• Projects mentioned:
  • tmux
  • Calva
  • clojure-lsp
• Libraries mentioned:
  • next.jdbc
  • Honey SQL