Allowed built-in functions
Elemental Inference allows the following built-in functions in both expressions. A call to any other
built-in fails the evaluation. Elemental Inference rejects such a call when you save the function, except
in the response expression of a model function, where it fails at run time. For more
information, see Writing function expressions.
Type conversion
| Function | Description | Example | Result |
|---|
$string(value) | Converts to a string. Serializes an object or array. | $string(200) | "200" |
$number(value) | Converts to a number | $number("42") | 42 |
$boolean(value) | Converts to a boolean | $boolean(1) | true |
Introspection
| Function | Description | Example | Result |
|---|
$length(string) | Length of a string | $length("hello") | 5 |
$count(array) | Number of elements in an array | $count(media.frames) | 4 |
$exists(value) | Whether a value exists | $exists(media.contextual.summary) | true or false |
$keys(object) | The key names of an object | $keys(media.contextual) | ["summary", "categories", ...] |
String
| Function | Description | Example | Result |
|---|
$uppercase(string) | Converts to uppercase | $uppercase("hello") | "HELLO" |
$lowercase(string) | Converts to lowercase | $lowercase("Hello") | "hello" |
$trim(string) | Removes leading and trailing whitespace | $trim(" hi ") | "hi" |
$substring(string, start, length) | Extracts a substring, starting at zero | $substring("abcdef", 2, 3) | "cde" |
$contains(string, pattern) | Whether a string contains a pattern | $contains(media.transcript, "penalty") | true or false |
$match(string, pattern) | Matches a string against a regular expression | $match("abc-123", /[0-9]+/) | The match details |
$replace(string, pattern, replacement) | Replaces matches | $replace("hello", "l", "r") | "herro" |
$split(string, separator) | Splits a string into an array | $split("a,b,c", ",") | ["a", "b", "c"] |
$join(array, separator) | Joins an array into a string | $join(media.contextual.categories, ", ") | "Basketball, Television" |
Regular expressions use RE2 syntax, which doesn't support backreferences or
lookaround.
Numeric
| Function | Description | Example | Result |
|---|
$sum(array) | Sum | $sum([1, 2, 3]) | 6 |
$max(array) | Largest value | $max([10, 5, 20]) | 20 |
$min(array) | Smallest value | $min([10, 5, 20]) | 5 |
$average(array) | Arithmetic mean | $average([10, 20, 30]) | 20 |
$abs(number) | Absolute value | $abs(-7) | 7 |
$floor(number) | Rounds down | $floor(3.9) | 3 |
$round(number, precision) | Rounds to a precision | $round(3.456, 2) | 3.46 |
Array
| Function | Description | Example | Result |
|---|
$append(array1, array2) | Concatenates two arrays. The usual way to put prompt text before mapped media. | $append([1, 2], [3, 4]) | [1, 2, 3, 4] |
$reverse(array) | Reverses the order | $reverse([1, 2, 3]) | [3, 2, 1] |
$sort(array) | Sorts the array | $sort([3, 1, 2]) | [1, 2, 3] |
$distinct(array) | Removes duplicates | $distinct([1, 2, 2, 3]) | [1, 2, 3] |
$map(array, function) | Applies a function to each element | $map([1,2,3], function($v){$v*2}) | [2, 4, 6] |
$filter(array, function) | Keeps the elements for which the function returns true | $filter([1,2,3,4], function($v){$v > 2}) | [3, 4] |
$reduce(array, function, init) | Reduces an array to one value | $reduce([1,2,3], function($a,$b){$a+$b}, 0) | 6 |
Object
| Function | Description | Example | Result |
|---|
$merge(array) | Merges an array of objects into one object | $merge([{"a":1}, {"b":2}]) | {"a":1,"b":2} |
$lookup(object, key) | Reads a value by key name | $lookup(media.contextual, "summary") | The value of summary |
$each(object, function) | Applies a function to each key-value pair | $each({"a":1}, function($v,$k){$k & "=" & $v}) | ["a=1"] |
Boolean, encoding, date and time, and JSON
| Function | Description | Example |
|---|
$not(value) | Logical NOT | $not($exists(media.transcript)) |
$random() | A random number from 0 up to but not including 1 | $random() > 0.5 ? "a" : "b" |
$encodeUrl(string) | URL-encodes a string, preserving structural characters such as / and ? | $encodeUrl("https://example.com/a b") |
$encodeUrlComponent(string) | URL-encodes one component, encoding all special characters | $encodeUrlComponent("a&b=c") |
$decodeUrl(string) | Decodes a URL-encoded string | $decodeUrl("a%20b") |
$decodeUrlComponent(string) | Decodes a URL-encoded component | $decodeUrlComponent("a%26b") |
$base64encode(string) | Encodes to Base64 | $base64encode("hello") |
$base64decode(string) | Decodes from Base64 | $base64decode("aGVsbG8=") |
$now() | The current time as an ISO 8601 string | $now() |
$millis() | The current time in milliseconds since the epoch | $millis() |
$toMillis(string) | Converts an ISO 8601 string to milliseconds | $toMillis("2026-01-15T12:00:00.000Z") |
$fromMillis(number) | Converts milliseconds to an ISO 8601 string | $fromMillis(1768478400000) |
$parse(string) | Parses a JSON string into data. Use it in a response expression when you asked the model for JSON. | $parse(content[type = "text"][0].text) |
$random() produces a new value each time it is evaluated. To use the
same value in two places, bind it first: ($r := $random(); ...).
Functions that are not allowed
Any built-in that isn't listed in the preceding tables is blocked, including
$pad() and $eval(). $pad() can allocate an
unbounded amount of memory inside a single call, and $eval() would let an
expression build and run new code at run time.
The transform operator (~> | location |
update |) is also unavailable, because it calls
$clone(), which isn't allowed. Build the object you want with an object
constructor or $merge() instead.
