Control Flow Guide

Master conditionals and loops in templates.

If/Elsif/Else Conditionals

Control rendering based on conditions.

Simple If

Render content only when condition is true:

{% if user.active %}
  Welcome back!
{% endif %}

If user.active is falsy, the content is not rendered.

If/Else

Provide alternative content:

{% if user.active %}
  Welcome back!
{% else %}
  Please activate your account
{% endif %}

Multiple Conditions (If/Elsif/Else)

Check multiple conditions in order:

{% if user.role == "admin" %}
  Admin Dashboard
{% elsif user.role == "moderator" %}
  Moderation Panel
{% elsif user.role == "user" %}
  User Dashboard
{% else %}
  Guest Area
{% endif %}

The first true condition renders; rest are skipped.

Nested Conditionals

Conditions can be nested:

{% if user %}
  Name: {{ user.name }}
  {% if user.email %}
    Email: {{ user.email }}
  {% endif %}
{% endif %}

Conditions

Comparisons

{{ 5 > 3 }}          # true
{{ 5 < 3 }}          # false
{{ 5 == 5 }}         # true
{{ 5 != 3 }}         # true
{{ 5 >= 5 }}         # true
{{ 5 <= 10 }}        # true

Use comparisons in if statements:

{% if age >= 18 %}
  Adult
{% else %}
  Minor
{% endif %}

String Comparisons

{% if user.name == "Alice" %}
  Hi Alice!
{% endif %}

{% if status != "active" %}
  Inactive account
{% endif %}

Logical Operators

Combine conditions with and, or, not:

{% if user.active and user.verified %}
  Fully verified
{% endif %}

{% if user.admin or user.moderator %}
  Staff member
{% endif %}

{% if not user.banned %}
  Account is good
{% endif %}

Complex Conditions

Use parentheses for clarity:

{% if (age >= 18 and verified) or admin %}
  Can proceed
{% endif %}

{% if (status == "active") and not (role == "banned") %}
  Show content
{% endif %}

Truthiness

Values are evaluated as truthy or falsy:

Falsy:

• nil (null)
• false
• "" (empty string)
• [] (empty list)
• {} (empty map/object)

Truthy:

• Everything else, including:
  • true
  • Non-empty strings: "hello"
  • Numbers: 0, 1, -1 (all numbers are truthy)
  • Non-empty lists
  • Non-empty maps

Using Truthiness

Check if value exists:

{% if user.email %}
  Email: {{ user.email }}
{% endif %}

This renders only if email is defined and not empty.

Check if list has items:

{% if items %}
  {{ items | length }} items found
{% else %}
  No items
{% endif %}

Inline Conditionals

Render conditionals on a single line:

Status: {% if active %}Active{% else %}Inactive{% endif %}

{% if premium %}🌟{% endif %} {{ user.name }}

For Loops

Iterate over collections.

Basic Loop

{% for item in items %}
  {{ item }}
{% endfor %}

This repeats the content for each item in the array.

Loop Over Objects

{% for user in users %}
  Name: {{ user.name }}
  Email: {{ user.email }}
{% endfor %}

Each user has access to all properties.

Nested Loops

{% for category in categories %}
  Category: {{ category.name }}
  {% for item in category.items %}
    - {{ item }}
  {% endfor %}
{% endfor %}

Loop with Conditionals

{% for item in items %}
  {% if item.available %}
    <li>{{ item.name }}</li>
  {% endif %}
{% endfor %}

Loop Variables

Access loop metadata with forloop:

{% for item in items %}
  {{ forloop.index }}: {{ item }}
{% endfor %}

Available Variables

• forloop.index - Position (1-based: 1, 2, 3...)
• forloop.index0 - Position (0-based: 0, 1, 2...)
• forloop.first - Boolean, true on first iteration
• forloop.last - Boolean, true on last iteration
• forloop.length - Total number of items

Examples

Number each item:

{% for item in items %}
  {{ forloop.index }}. {{ item }}
{% endfor %}

Mark first and last:

{% for item in items %}
  {% if forloop.first %}
    (First) {{ item }}
  {% elsif forloop.last %}
    (Last) {{ item }}
  {% else %}
    {{ item }}
  {% endif %}
{% endfor %}

Add separators:

{% for item in items %}
  {{ item }}{% unless forloop.last %}, {% endunless %}
{% endfor %}

Output: Item1, Item2, Item3

Alternate rows:

{% for item in items %}
  {% if forloop.index0 | modulo(2) == 0 %}
    <tr class="even">
  {% else %}
    <tr class="odd">
  {% endif %}
    <td>{{ item }}</td>
  </tr>
{% endfor %}

Progress indicator:

{% for item in items %}
  [{{ forloop.index }}/{{ forloop.length }}] {{ item }}
{% endfor %}

Empty Loop Handling

Check if loop will run:

{% if items %}
  {% for item in items %}
    {{ item }}
  {% endfor %}
{% else %}
  No items to display
{% endif %}

Or with length filter:

{% if items | length > 0 %}
  Found {{ items | length }} items
{% else %}
  No items found
{% endif %}

Control Patterns

Conditional List Items

<ul>
{% for item in items %}
  {% if item.active %}
    <li>{{ item.name }}</li>
  {% endif %}
{% endfor %}
</ul>

Role-Based Display

{% if user.admin %}
  <div class="admin-tools">
    <button>Ban User</button>
    <button>Edit Settings</button>
  </div>
{% elsif user.moderator %}
  <div class="mod-tools">
    <button>Warn User</button>
  </div>
{% endif %}

Permission Checks

{% if user.can_edit_post %}
  <button class="edit">Edit</button>
{% endif %}

{% if user.can_delete_post and post.owner == user.id %}
  <button class="delete">Delete</button>
{% endif %}

Status Indicators

{% for order in orders %}
  <div class="order">
    Order #{{ order.id }}
    {% if order.status == "pending" %}
      <span class="pending">Pending</span>
    {% elsif order.status == "shipped" %}
      <span class="shipped">Shipped</span>
    {% elsif order.status == "delivered" %}
      <span class="delivered">Delivered</span>
    {% else %}
      <span class="unknown">Unknown</span>
    {% endif %}
  </div>
{% endfor %}

Pagination Indicators

Page {{ current_page }} of {{ total_pages }}

{% if current_page > 1 %}
  <a href="?page={{ current_page | minus(1) }}">Previous</a>
{% endif %}

{% if current_page < total_pages %}
  <a href="?page={{ current_page | plus(1) }}">Next</a>
{% endif %}

Default Values

{% if user.bio %}
  Bio: {{ user.bio }}
{% else %}
  Bio: Not provided
{% endif %}

Or with filters:

Name: {{ user.name | default("Anonymous") }}

Common Mistakes

Wrong Operator

{# Wrong - string comparison #}
{% if items == [] %}

{# Right - check length #}
{% if items | length == 0 %}

{# Or - check truthiness #}
{% if items %}

Missing Endif

{# Syntax error #}
{% if condition %}
  Content

{# Correct #}
{% if condition %}
  Content
{% endif %}

Truthiness Confusion

{# 0 is truthy in Mau #}
{% if count == 0 %}
  No items
{% endif %}

{# Not this #}
{% if not count %}
  (0 is truthy, this won't work)
{% endif %}

Advanced Patterns

Ternary-like Pattern

Simulate ternary with inline if:

Status: {% if active %}Online{% else %}Offline{% endif %}

Guard Clauses

Use early returns with negation:

{% if not user %}
  Please log in
{% else %}
  Welcome {{ user.name }}
{% endif %}

Multi-Level Conditions

{% if user %}
  {% if user.admin %}
    Admin: {{ user.name }}
  {% elsif user.active %}
    Active: {{ user.name }}
  {% else %}
    Inactive: {{ user.name }}
  {% endif %}
{% else %}
  No user
{% endif %}

Summary

See Also

• Template Language Reference - Expression syntax
• Variables Guide - Variable access patterns
• Filters Guide - Using filters in conditions