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Mutants Assembleλ︎

In this section you will apply changes to values, how to define your own simple functions.

We will also introduce the following functions for the first time:

function Description
atom create an anonymous function, one without a name
deref, @ assign a name to a function

Create a new Clojure projectλ︎

Pracitcalli Clojure CLI Config provides the :project/create alias to create projects using deps-new project.

clojure -T:project/create :template app :name practicalli/mutants-assemble

Open the src/practicalli/mutants_assemble.clj file in a Clojure aware editor and start the REPL.

Define an atomλ︎

Use the def function to bind a name to an atom.

The atom wraps data, initially an empty vector.

(def mutants (atom []))

The vector remains an immutable value, even though it is contained within a mutable atom container

Define a function using defn which takes a mutant as an argument and updates the value managed by the atom. The reference to the atom is also an argument, making this a pure function and more generic as any given atom can be updated with this function.

(defn add-mutant [mutants mutant]
  (swap! mutants conj mutant))

swap! uses a function to create a new value for the atom to manage. In this case the conj function is used to join the value of mutant with the existing mutants atom value, creating a new vector.

swap! is a macro so the syntax is a little different. Essentially this is the same as an expression (conj mutants mutant), with the value this returns swapped into the atom.

Call the function with the mutants atom and a mutant to add, which is a string containing the name of a mutant character.

(add-mutant mutants "Black Widow")

The value the atom is managing has been swapped for a new value. The original value was not modified (vectors are immutable) so the atom now points to a new value, a vector containing a string.

Viewing the value managed by the atomλ︎

Use the deref function to see the value the atom is managing.

(deref mutants)

It is idiomatic to use @ which is a syntax alias for the deref function, rather than explicitly using deref.


Reset the atom valueλ︎

reset! will change the value managed by the atom by providing the new value. This is simpler than using swap! as it does not use the existing value in the atom.

(reset! mutants [])

Now all the mutants are gone (and we can start looking for new ones to add).