Private Functions in Clojure

Clojure developers coming from Object Oriented backgrounds know how useful it is to separate implementation details from functions and methods that are supposed to be used by other coders. Java has public and private methods. This allows devs to limit usage and visibility of functions that are not meant to be used directly.

There are two options in Clojure for keeping functions private. First, you can use a special macro, defn- . defn-  works just like defn , except that the function is only visible inside the current namespace. This makes the function private in the Java sense to the term. Continue reading “Private Functions in Clojure”

Clojure REPL for Development

A common way to develop code (don’t blame the messenger) is to start the application watch for the logged errors, make changes and then restart the application again, looking for more logged errors.

That’s not how it’s done in the world of Clojure, not just because it’s bad, but because the process of starting any Clojure program is horribly slow. Instead, in Clojure normally you start the application and then connect with a terminal window running a Clojure REPL. For example, if you are running a Luminus server, when you start it, it will tell you what port the server is listening for REPL connections on.

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Clojure Destructuring with Functions

In clojure terms, destructuring is taking apart a sequence and putting the pieces you care about into variables you can more easily work with. Destructuring involves square brackets that make it look like a vector, but it is really binding a variable from a given seq to a new variable. Let’s look at an example involving a function in Clojure.

Notice the -main function has three variables in a vector: a site address, a web page, and a user name. It is much easier in the new function to unpackage these variables form the vector and bind them to variables that have meaningful names, and then use the names.

The result is as follows.

What if we have more values in the seq than values we intend to bind to? For example, below we added an additional index with the words “random stuff”.

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