Elixir Doctests Error Fix

The Hook

You will learn how to fix common doctests 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

Doctests

The wrong approach and the correct fix are shown below:

Wrong:

defmodule Math do
  @doc """
  Adds two numbers
  ## Examples
      iex> Math.add(1, 2)
      3
  """
  def add(a, b), do: a + b
end

Output:

Right:

defmodule Math do
  @doc """
  Adds two numbers
  ## Examples
      iex> Math.add(1, 2)
      3
      iex> Math.add(-1, 1)
      0
  """
  def add(a, b), do: a + b
end
doctest Math

Output:

Prevention

Doctests embed examples in @doc. Verified with doctest Macro.

Common Mistakes with doctests

1. Using return to exit a function early instead of wrapping a pure value in the monad
2. Mixing let bindings with <- bindings in do notation, producing type errors
3. Overlapping type class instances that cause GHC to reject the program with ambiguous dispatch errors

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