Ep 041: Why Do Clojurians Make Such a Big Deal About Immutability?

Functional Design in Clojure

Each week, we answer a different question about Clojure and functional programming.

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

This week, the question is: "Why do Clojurians make such a big deal about immutability?" We cover several practical side effects of immutability and why we've become such big fans of data that doesn't let us down.

Selected quotes:

• "Well, we don't have Monads to talk about."
• "What good is a program, if you can't change stuff!?"
• "The memory cost of data structures is in proportion to the changes, not the users."
• "I can hang on to a reference to the old state and a reference to the new state very cheaply."
• "You can reduce comparison to referential equality."
• "Once you can efficiently save every version of the state, going back to a previous version is no big deal."
• "I love determinism. Determinism is trustable."
• "I can trust immutable data. And if I can trust it, then it can occupy a smaller part of my brain."

Related episodes:

• 002: Tic-Tac-Toe, State in a Row
• 039: Why use Clojure over another functional language?