Variable Access Operators

These operators access data from the evaluation context.

Feature flags (Rust crate). var and val are baseline; exists requires the ext-control feature. Every language binding enables all operator features. See the feature table.

var

Access a value from the data object using dot notation.

Syntax:

{ "var": "path" }
{ "var": ["path", default] }

Arguments:

• path - Dot-separated path to the value (string)
• default - Optional default value if path doesn’t exist

Returns: The value at the path, or the default value, or null.

Examples:

// Simple access
{ "var": "name" }
// Data: { "name": "Alice" }
// Result: "Alice"

// Nested access
{ "var": "user.address.city" }
// Data: { "user": { "address": { "city": "NYC" } } }
// Result: "NYC"

// Array index access
{ "var": "items.0" }
// Data: { "items": ["a", "b", "c"] }
// Result: "a"

// Default value
{ "var": ["missing", "default"] }
// Data: {}
// Result: "default"

// Access entire data object
{ "var": "" }
// Data: { "x": 1, "y": 2 }
// Result: { "x": 1, "y": 2 }

Try it:

Notes:

• Empty string "" returns the entire data context
• In array operations (map, filter, reduce), "" refers to the current element
• Numeric indices work for both arrays and string characters
• Returns null if path doesn’t exist and no default is provided

val

Alternative variable access with additional path navigation capabilities.

Syntax:

{ "val": "path" }
{ "val": ["path", default] }

Arguments:

• path - Path to the value, supports additional navigation syntax
• default - Optional default value

Returns: The value at the path, or the default value, or null.

Examples:

// Simple access (same as var)
{ "val": "name" }
// Data: { "name": "Bob" }
// Result: "Bob"

// Nested access (use the array form; a dot string is NOT split)
{ "val": ["config", "settings", "enabled"] }
// Data: { "config": { "settings": { "enabled": true } } }
// Result: true

// A dot-path string is treated as a single literal key, so it does NOT navigate
{ "val": "config.settings.enabled" }
// Data: { "config": { "settings": { "enabled": true } } }
// Result: null (looks up the key "config.settings.enabled", which is absent)

Try it:

Notes:

• val does NOT support var’s dot-path strings: a string argument is a single literal key, so { "val": "a.b" } looks up the key "a.b", it does not descend into a then b
• For nested access use the array form { "val": ["a", "b"] }, where each element is one path segment
• Useful for complex data navigation where path segments are computed

exists

Check if a variable path exists in the data.

Syntax:

{ "exists": "key" }
{ "exists": ["key1", "key2", ...] }
{ "exists": { "var": "path" } }

Arguments:

• key - A single top-level key (string), or
• ["key1", "key2", ...] - An array of path segments for nested access, or
• A var operation that resolves to the key/path to check

Returns: true if the path exists, false otherwise.

Examples:

// Check if key exists
{ "exists": "name" }
// Data: { "name": "Alice" }
// Result: true

// Check missing key
{ "exists": "age" }
// Data: { "name": "Alice" }
// Result: false

// Check nested path (use the array form; a dot string is one literal key)
{ "exists": ["user", "profile"] }
// Data: { "user": { "profile": { "name": "Bob" } } }
// Result: true

// A dot-path string checks a single literal key, so it does not descend
{ "exists": "user.profile" }
// Data: { "user": { "profile": { "name": "Bob" } } }
// Result: false (no top-level key named "user.profile")

// Check with var
{ "exists": { "var": "fieldName" } }
// Data: { "fieldName": "name", "name": "Alice" }
// Result: true (checks if "name" exists)

Try it:

Notes:

• Returns false for paths that don’t exist
• Does not check if the value is null/empty, only if the path exists
• Useful for conditional logic based on data structure