---

name: scl-expressions description: Comprehensive guide to SCL's dynamic expression language ($var, $jq, pipelines).

SCL Expressions Skill

1. The Expression Syntax

SCL allows dynamic values using backtick expressions: `...`. Inside backticks, you can call functions and pipe data.

Canonical Example:

Copy# Get ID from variable 'meta', filter with jq, and extract ID
table_id `$var('meta') |> $jq('.tables[] | select(.name == "user") | .id')`

2. Variables (var)

Variables define reusable data blocks. They are commonly used to store GraphQL query results for use in subsequent set blocks.

Syntax:

Copyvar my_variable_name {
  # A. GraphQL Query
  query ```
  query {
    tables: dev_simple_system__tables { id name }
  }

B. Static JSON

value ``` { "api_key": "12345", "retries": 3 }

Copy}

3. Function Reference

$var(name)

• Purpose: Retrieves the value of a named variable defined earlier in the file.
• Returns: JSON Object (result of query) or Value.
• Example: $var('metadata')

$jq(filter)

• Purpose: Transforms JSON input using a jq filter string.
• Common Patterns:
  • .field: Access property.
  • .[]: Iterate array.
  • select(.x == "y"): Filter array items.
  • map(.id): Transform array.
  • .users[0].id: Deep access.
• Example: $jq('.tables[] | select(.name == "order") | .id')

$json()

• Purpose: Parses a string into a JSON object. Useful when setting configuration fields that expect :json type.
• Example:

  Copyoperations `["insert", "update"] |> $json()`
  

$file(path)

• Purpose: Reads the contents of a file relative to the app root.
• Common Use: Loading scripts for Record Behaviors.
• Example: $file('scripts/record-behaviors/user.js')

$env(key)

• Purpose: Accessing environment variables (e.g., API Keys).
• Example: $env('STRIPE_SECRET_KEY')

$encode_image(path)

• Purpose: Loads an image file as a Base64 Data URI.
• Example: $encode_image('assets/logo.png')

4. Common Patterns

Pattern A: Dynamic ID Lookup

When creating metadata, logic, or binding records, you need the UUIDs of tables/fields.

Copy# 1. Fetch Metadata
var meta {
  query ```
  query {
    tables: dev_simple_system__tables(where: { application_id: {_eq: "com.acme.app"} }) {
      id name
    }
  }

}

2. Use ID

set dev_simple_system.record_behavior, user_behavior {

dynamic lookup

table_id $var('meta') |> $jq('.tables[] | select(.name == "user") | .id') }

Copy
### Pattern B: Injection
Injecting configuration into a JSON field.

```scl
var config {
  value `{ "theme": "dark", "notifications": true }`
}

set dev_simple_system.setting, app_config {
  value `$var('config') |> $json()`
}