Pure Functions

Pure Functions

In this lesson — part of Functional Foundations — you'll learn pure functions in Elm and why it matters in real work.

Why it matters

Functional style — pure functions and immutability — makes code easier to test and reason about.

Key ideas

• Pure functions
• Immutability
• No shared mutable state
• Predictable outputs

In practice

Here's the idea in pseudocode — the exact syntax varies by language:

// Elm: pure function
function double(n) { return n * 2 }

Try it yourself

Exercise: In Elm, rewrite a function that mutates a global so it's pure.

Recap

You now understand pure functions and can apply it in Elm. Mark this lesson complete and continue to the next one.