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DocumentationWorking with YAML Schemas⚡ Template Expressions

⚡ Template Expressions

Loopstack uses two distinct expression syntaxes for dynamic content rendering and data access throughout your automation configurations.

Expression Syntax Overview

Template Expressions ({{ }}) - Used for rendering dynamic content within text, typically in tool arguments, message content, and document templates:

transitions:
    # ...
  - id: next
    from: signup_received
    to: user_email_notified
    call:
      - tool: EmailTool
        arguments:
          subject: "Welcome {{user.name}}!"                    # Template expression that evaluates to a string
          body: |
            Hello {{user.name}},
 
            {{#if user.isPremium}}
              Thank you for being a premium member!
            {{else}}
              Consider upgrading to premium for more features.
            {{/if}}
 
            Best regards,
            The Team

Property Accessors (${ }) - Used for accessing variables and context data in YAML configuration values:

transitions:
    # ...
  - id: next
    from: signup_received
    to: user_email_notified
    call:
      - tool: DataProcessingHandler
        arguments:
          user_id: ${ ctx.workflow.user_id }
          input_data: ${ inputData }              # add Property directly, preserving data type

Both syntaxes can access the same underlying data, but serve different purposes:

  • Template expressions render dynamic text content with conditional logic and formatting (always outputs strings)
  • Property accessors inject raw data values into configuration parameters while preserving the original data type (string, object, array, boolean, etc.)

Template Expressions {{ }}

Loopstack uses Handlebars for rendering Template Expressions. Template Expressions can utilize a range of different Handlebars features and helpers:

Handlebars Syntax

Simple variable

{{myData.name}}

Nested property

{{myData.profile.email}}

Array access

{{myData.items.[0]}}

Default Helpers

if

{{#if myData.isActive}}Welcome back!{{/if}}

if/else

{{#if myData.isAdmin}}Admin Panel{{else}}User Panel{{/if}}

unless

{{#unless myData.isBlocked}}Access granted{{/unless}}

each

{{#each myData.users}}<li>{{this.name}}</li>{{/each}}

each with else

{{#each myData.items}}{{this}}{{else}}No items{{/each}}

Comparison and Logic Helpers

eq

strict equality

{{#if (eq myData.role "admin")}}Admin{{/if}}

ne

strict inequality

{{#if (ne myData.status "inactive")}}active{{/if}}

looseEq

loose equality

{{#if (looseEq myData.count "5")}}Five{{/if}}

looseNe

loose inequality

{{#if (looseNe myData.value null)}}Has value{{/if}}

gt

greater than

{{#if (gt myData.age 18)}}Adult{{/if}}

gte

greater than or equal

{{#if (gte myData.score 90)}}Perfect!{{/if}}

lt

less than

{{#if (lt myData.cold 32)}}Freezing{{/if}}

lte

less than or equal

{{#if (lte myData.age 30)}}Young adult{{/if}}

and

{{#if (and myData.isActive myData.isVerified)}}Verified user{{/if}}

or

{{#if (or myData.isPremium myData.isTrial)}}Premium features{{/if}}

not

{{#if (not myData.isBlocked)}}Welcome{{/if}}

contains

{{#if (contains myData.email "@company.com")}}Employee{{/if}}

startsWith

{{#if (startsWith myData.doctor "Dr.")}}Doctor{{/if}}

endsWith

{{#if (endsWith myData.file.name ".pdf")}}PDF file{{/if}}

regexTest

{{#if (regexTest myData.phone "^\\+1")}}US number{{/if}}

regexTest with flags {{#if (regexTest myData.email "^[A-Z]+@" "i")}}Valid email{{/if}}

in

in (array)

{{#if (in myData.role myData.validRoles)}}Valid role{{/if}}

in (object) {{#if (in "email" myData)}}Has email{{/if}}

length

Total: {{length myData.items}}

isEmpty

{{#if (isEmpty myData.empty)}}No tags{{/if}}

typeOf

Type: {{typeOf myData.value}}

isNull

{{#if (isNull myData.deletedAt)}}Active{{/if}}

isUndefined

{{#if (isUndefined myData.tempData)}}No temp data{{/if}}

isNumber

{{#if (isNumber myData.age)}}Age: {{myData.age}}{{/if}}

isString

{{#if (isString myData.bio)}}{{myData.bio}}{{/if}}

isBoolean

{{#if (isBoolean myData.flag)}}Boolean value{{/if}}

isArray

{{#if (isArray myData.items)}}List of items{{/if}}

isObject

{{#if (isObject myData)}}User object{{/if}}

Mathematical Operations

add

Total: ${{add myData.price myData.tax myData.shipping}}

subtract

Discount: ${{subtract myData.original myData.sale}}

multiply

Tax: ${{multiply myData.price 0.08}}

divide

Average: {{divide myData.total myData.count}}

modulo

Remainder: {{modulo 17 5}}

Utility Helpers

default

Name: {{default myData.displayName myData.username}}

Date and Time

Current Date

currentDate

Today: {{currentDate}}

currentDate with format {{currentDate "yyyy-MM-dd"}}

currentDate with time {{currentDate "yyyy-MM-dd h:mm"}}

Date Formatting

formatDate

Created: {{formatDate myData.createdAt}}

formatDate with format {{formatDate myData.event.date "yyyy-MM-dd"}}

Time Ago

timeAgo

Last seen: {{timeAgo myData.lastLoginAt}}

timeAgo for comments Posted {{timeAgo myData.comment.createdAt}}

timeAgo for events Event ended {{timeAgo myData.event.endDate}}

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