Elixir Lists Error Fix

The Hook

You will learn how to fix common lists errors. This matters because understanding this concept is essential for productive development. Built by the developers of Doda Browser, DodaZIP, and Durga Antivirus Pro.

Quick Fix

Lists

The wrong approach and the correct fix are shown below:

Wrong:

list = [1, 2, 3]
IO.inspect(length(list))

Output:

Right:

list = [1, 2, 3]
[0 | list] # cons: [0, 1, 2, 3]
list ++ [4, 5] # concatenation
List.flatten([[1], [2]]) # [1, 2]
Enum.map(list, fn x -> x * 2 end)

Output:

Prevention

Lists are linked lists. Cons (|) prepends. ++ appends (slow).

Common Mistakes with lists

1. Forgetting deriving (Show, Eq) on custom data types needed for debugging
2. Placing the wildcard pattern first in case expressions, making all subsequent patterns unreachable
3. Using head and tail instead of pattern matching, causing runtime errors on empty lists

These mistakes appear frequently in real-world ELIXIR code. DodaTech's contributors have identified these patterns through analysis of open-source projects and production systems.

Practice Exercise

Write a pure function that safely divides two integers using Maybe, then test it with edge cases like division by zero and negative numbers.

This exercise reinforces the concepts covered in this guide. Try implementing it before checking online solutions.

FAQ