Your First Template

Build a complete, realistic template from scratch.

Project: User Profile Page

We'll create a user profile page template that displays user information with conditional sections.

Step 1: Define Your Context

First, gather the data you want to display:

context = %{
  "user" => %{
    "name" => "Alice Johnson",
    "email" => "alice@example.com",
    "role" => "admin",
    "active" => true,
    "joined_date" => "2023-01-15",
    "profile" => %{
      "bio" => "Passionate about Elixir and functional programming",
      "location" => "San Francisco, CA",
      "website" => "https://alice.dev"
    }
  },
  "company" => %{
    "name" => "Tech Startup Inc",
    "industry" => "Software Development"
  },
  "projects" => [
    %{"name" => "Phoenix API", "status" => "active"},
    %{"name" => "Elixir Utilities", "status" => "active"},
    %{"name" => "Old Project", "status" => "archived"}
  ]
}

Step 2: Write the Template

Create a template that renders the profile:

template = """
# {{ user.name }}

**Role:** {{ user.role | capitalize }}
**Email:** {{ user.email }}
**Status:** {% if user.active %}Active{% else %}Inactive{% endif %}
**Member Since:** {{ user.joined_date }}

## Bio
{{ user.profile.bio }}

## Contact Information
- **Location:** {{ user.profile.location }}
- **Website:** {{ user.profile.website }}
- **Company:** {{ company.name }} ({{ company.industry }})

## Projects ({{ projects | length }})
{% for project in projects %}
- **{{ project.name }}** - {{ project.status | capitalize }}
{% endfor %}

{% if user.role == "admin" %}

## Admin Section
You have administrative privileges in this system.

### Quick Actions
- Manage Users
- System Settings
- View Logs

{% endif %}
"""

Step 3: Render the Template

{:ok, result} = Mau.render(template, context)
IO.puts(result)

Expected Output

# Alice Johnson

**Role:** Admin
**Email:** alice@example.com
**Status:** Active
**Member Since:** 2023-01-15

## Bio
Passionate about Elixir and functional programming

## Contact Information
- **Location:** San Francisco, CA
- **Website:** https://alice.dev
- **Company:** Tech Startup Inc (Software Development)

## Projects (3)
- **Phoenix API** - Active
- **Elixir Utilities** - Active
- **Old Project** - Archived

## Admin Section
You have administrative privileges in this system.

### Quick Actions
- Manage Users
- System Settings
- View Logs

Walkthrough: What's Happening

1. Simple Interpolation

{{ user.name }}  →  "Alice Johnson"

Access nested properties with dot notation.

2. Filters

{{ user.role | capitalize }}  →  "Admin"

Transforms the value before display.

3. Conditionals

{% if user.active %}Active{% else %}Inactive{% endif %}

Renders different text based on conditions.

4. List Length

{{ projects | length }}  →  "3"

Count items in a collection.

5. Loops

{% for project in projects %}
  - **{{ project.name }}** - {{ project.status | capitalize }}
{% endfor %}

Iterates through each item in the list.

6. Role-Based Sections

{% if user.role == "admin" %}
  {# Admin content #}
{% endif %}

Show different content based on user role.

Variations and Exercises

Exercise 1: Add Member Status Badge

Modify the status line to show different badges:

**Status:**
{% if user.active %}
  🟢 Active
{% else %}
  🔴 Inactive
{% endif %}

Exercise 2: Filter Active Projects

Show only active projects:

## Active Projects
{% for project in projects %}
  {% if project.status == "active" %}
    - {{ project.name }}
  {% endif %}
{% endfor %}

Exercise 3: Add Last Login

Add to context:

context = %{
  # ... existing data
  "last_login" => "2024-01-29T14:30:00Z"
}

Then in template:

**Last Login:** {{ last_login }}

Exercise 4: Role-Based Menu

{% if user.role == "admin" %}
  [Admin Dashboard]
{% elsif user.role == "moderator" %}
  [Moderation Panel]
{% else %}
  [User Settings]
{% endif %}

Common Patterns

1. Conditional Rendering

{% if user.profile.bio %}
  <div class="bio">{{ user.profile.bio }}</div>
{% endif %}

This checks if bio exists before showing it.

2. List with Fallback

{% if projects %}
  {% for project in projects %}
    - {{ project.name }}
  {% endfor %}
{% else %}
  No projects yet
{% endif %}

3. Formatted Lists

{% for project in projects %}
  {% if forloop.first %}(1){% else %}, ({{ forloop.index }}){% endif %} {{ project.name }}
{% endfor %}

Output: (1) Phoenix API, (2) Elixir Utilities, (3) Old Project

4. Empty vs Populated

{% if user.projects %}
  Projects: {{ user.projects | join(", ") }}
{% else %}
  No projects
{% endif %}

Debugging Tips

Check Your Context

Print context to verify data structure:

IO.inspect(context, pretty: true)

Test Small Pieces

Before building the full template, test individual expressions:

Mau.render("{{ user.name }}", context)
Mau.render("{{ user.role | capitalize }}", context)

Handle Missing Data

Always check if data exists before accessing it:

{% if user.profile %}
  Bio: {{ user.profile.bio }}
{% endif %}

Preview Output

Render to a temporary file and check formatting:

{:ok, result} = Mau.render(template, context)
File.write!("preview.txt", result)

Next Steps

Now that you understand the basics, explore more advanced features:

• Filters Guide - More powerful filters
• Control Flow Guide - Advanced conditionals
• Map Directives Guide - Transform nested data
• Report Generation Example - Real-world use cases

Key Takeaways

✅ Templates combine text, variables, and logic ✅ Use {{ }} for dynamic content ✅ Use {% %} for logic (if, for) ✅ Chain filters with | to transform data ✅ Conditionals show/hide content ✅ Loops iterate over collections ✅ Always handle missing or empty data

You're ready to build templates! Start with simple examples and gradually add complexity.