Advanced Logic

This guide covers advanced Liquid patterns for power users who need to implement complex business logic, state management, and data transformations.

Advanced Liquid Patterns

Custom Helper Functions

While Liquid doesn't support custom functions directly, you can simulate them with assign blocks and variables.

{% comment %} Calculate tax helper {% endcomment %}
{% liquid
  assign _price = include.price
  assign _taxRate = include.taxRate | default: 0.1
  assign _tax = _price | times: _taxRate
  assign result = _tax
%}

{% comment %} Usage {% endcomment %}
{% liquid
  assign include = ""
  assign include.price = subtotal
  assign include.taxRate = 0.15
%}
Tax: ${{ result }}

State Machines

Create complex workflows with state tracking. This is useful for multi-step processes where the path depends on a combination of previous actions.

{% liquid
  assign state = current_state | default: "initial"
  assign nextState = ""

  case state
    when "initial"
      if has_account == "yes"
        assign nextState = "login"
      else
        assign nextState = "registration"
      endif

    when "login"
      if login_successful == "yes"
        assign nextState = "dashboard"
      else
        assign nextState = "password-reset"
      endif

    when "registration"
      if registration_complete == "yes"
        assign nextState = "verification"
      endif

    when "verification"
      if verified == "yes"
        assign nextState = "dashboard"
      endif
  endcase
%}

{{ nextState }}

Data Transformation Pipelines

Chain multiple transformations to clean and format data.

{% liquid
  assign raw = user_input
  assign cleaned = raw | strip | downcase
  assign words = cleaned | split: " "
  assign unique = words | uniq
  assign sorted = unique | sort_natural
  assign result = sorted | join: ", "
%}

Processed: {{ result }}

Common Advanced Patterns

Pattern 1: Multi-Stage Approval Workflow

{% liquid
  assign stage = approval_stage | default: "pending"
  assign nextStage = ""

  if stage == "pending"
    if manager_approved == "yes"
      assign nextStage = "director-review"
    else
      assign nextStage = "rejected"
    endif
  elsif stage == "director-review"
    if director_approved == "yes"
      assign nextStage = "final-approval"
    else
      assign nextStage = "rejected"
    endif
  elsif stage == "final-approval"
    if ceo_approved == "yes"
      assign nextStage = "approved"
    else
      assign nextStage = "rejected"
    endif
  endif

  echo nextStage
%}

Pattern 2: Dynamic Pricing Engine

{% liquid
  assign basePrice = base_price
  assign quantity = quantity

  # Volume discount
  if quantity >= 100
    assign volumeDiscount = 0.2
  elsif quantity >= 50
    assign volumeDiscount = 0.15
  elsif quantity >= 10
    assign volumeDiscount = 0.1
  else
    assign volumeDiscount = 0
  endif

  # Loyalty discount
  if loyalty_years >= 5
    assign loyaltyDiscount = 0.1
  elsif loyalty_years >= 2
    assign loyaltyDiscount = 0.05
  else
    assign loyaltyDiscount = 0
  endif

  # Calculate
  assign subtotal = basePrice | times: quantity
  assign volumeSavings = subtotal | times: volumeDiscount
  assign afterVolume = subtotal | minus: volumeSavings
  assign loyaltySavings = afterVolume | times: loyaltyDiscount
  assign total = afterVolume | minus: loyaltySavings
%}

Subtotal: ${{ subtotal }}
Volume Discount (-{{ volumeDiscount | times: 100 }}%): -${{ volumeSavings }}
Loyalty Discount (-{{ loyaltyDiscount | times: 100 }}%): -${{ loyaltySavings }}
Total: ${{ total }}

Pattern 3: Risk Assessment Scoring

{% liquid
  assign riskScore = 0

  # Age factor
  assign age = birth_date | diff_time: today, "year"
  if age < 25
    assign riskScore = riskScore | plus: 20
  elsif age < 35
    assign riskScore = riskScore | plus: 10
  endif

  # Income factor
  assign income = annual_income
  if income < 30000
    assign riskScore = riskScore | plus: 30
  elsif income < 60000
    assign riskScore = riskScore | plus: 15
  endif

  # Credit history
  if credit_score < 600
    assign riskScore = riskScore | plus: 40
  elsif credit_score < 700
    assign riskScore = riskScore | plus: 20
  endif

  # Determine level
  if riskScore >= 60
    assign riskLevel = "High"
    assign approved = false
  elsif riskScore >= 30
    assign riskLevel = "Medium"
    assign approved = true
  else
    assign riskLevel = "Low"
    assign approved = true
  endif
%}

Risk Score: {{ riskScore }}
Risk Level: {{ riskLevel }}
{% if approved %}Approved{% else %}Denied{% endif %}

Performance Optimization

Minimize Repeated Calculations

❌ Inefficient:

Total: {{ price | times: quantity | times: 1.1 }}
Tax: {{ price | times: quantity | times: 0.1 }}
Subtotal: {{ price | times: quantity }}

✅ Efficient:

{% assign subtotal = price | times: quantity %}
Subtotal: {{ subtotal }}
Tax: {{ subtotal | times: 0.1 }}
Total: {{ subtotal | times: 1.1 }}

Cache Complex Lookups

{% liquid
  assign userType = membership

  case userType
    when "platinum"
      assign discount = 0.25
      assign priority = 1
      assign support = "24/7"
    when "gold"
      assign discount = 0.15
      assign priority = 2
      assign support = "business hours"
    else
      assign discount = 0
      assign priority = 5
      assign support = "email only"
  endcase
%}

Avoid Nested Loops

❌ Slow:

{% for item in items %}
  {% for category in categories %}
    {% if item.category == category.id %}
      {{ item.name }} - {{ category.name }}
    {% endif %}
  {% endfor %}
{% endfor %}

✅ Better:

{% assign categoryMap = categories | map: "id" %}
{% for item in items %}
  {{ item.name }} - {{ categoryMap[item.category] }}
{% endfor %}

Debugging Techniques

Output Debugging

DEBUG: {{ values | json: 2 }}

Step-by-Step Tracing

{% liquid
  echo "Step 1: Input = " | append: input
  assign cleaned = input | strip
  echo "\nStep 2: Cleaned = " | append: cleaned
  assign processed = cleaned | upcase
  echo "\nStep 3: Processed = " | append: processed
%}

Conditional Debugging

{% if debug_mode == "yes" %}
  <pre>
  Values: {{ values | json: 2 }}
  Calculations:
  - Subtotal: {{ subtotal }}
  - Tax: {{ tax }}
  - Total: {{ total }}
  </pre>
{% endif %}