Expressions and functions

This page documents ABL’s expression language: operators, variable paths, {{}} template-string interpolation, the 36 built-in functions, and type coercion rules. Expressions are used in conditions (WHEN, CHECK, constraint rules), value assignments (SET), template interpolation ({{}}), and function calls. For rich content output formats (voice, cards, carousels, interactive actions, templates), see Rich content.

Expression syntax

Comparison operators

Operator	Syntax	Description
`==`	`a == b`	Equal to.
`!=`	`a != b`	Not equal to.
`>`	`a > b`	Greater than.
`<`	`a < b`	Less than.
`>=`	`a >= b`	Greater than or equal to.
`<=`	`a <= b`	Less than or equal to.
`in`	`a IN [x,y,z]`	Value is in the list.
`not_in`	`a NOT IN [x]`	Value is not in the list.
`matches`	`a matches r`	Value matches a regular expression.
`contains`	`a contains b`	String contains substring, or array contains element.
`startsWith`	`a startsWith b`	String starts with a prefix.
`endsWith`	`a endsWith b`	String ends with a suffix.

Logical operators

Operator	Syntax	Description
`AND`	`a AND b`	Both conditions must be true.
`OR`	`a OR b`	At least one must be true.
`NOT`	`NOT a`	Negates the condition.

Write logical operators in uppercase (AND, OR, NOT). ! is also accepted as a prefix negation.

Unary operators

Operator	Syntax	Description
`NOT` / `!`	`NOT condition` / `!condition`	Negates a condition.
`IS SET`	`var IS SET`	True if the variable is not null/undefined (empty string counts as set).
`IS NOT SET`	`var IS NOT SET`	True if the variable is null or undefined.
`is_number`	`var is_number`	True if the variable is a number.

Operator precedence

Parentheses ()
Unary operators (NOT, IS SET, IS NOT SET)
Comparison operators (==, !=, >, <, >=, <=, contains, matches)
AND
OR

Use parentheses to override default precedence:

WHEN: (status == "active" OR status == "pending") AND amount > 0

Variable paths and dot notation

Reference variables using dot notation to access nested values.

user.name                  # Access nested property
user.addresses[0].city     # Array index access
acctResult.status          # Tool result field

Path resolution rules

The evaluator looks up the full path in the session context.
The Platform resolves each segment left to right: user.address.city resolves user, then address on the result, then city.
If any segment resolves to null or undefined, the entire path resolves to undefined.
Array access uses bracket notation: items[0], items[2].name.

Template strings

Template strings use {{}} syntax for variable interpolation within RESPOND, summary, and other string properties — including inside a TEMPLATES: block body:

RESPOND: "Hello, {{customer_name}}! Your balance is {{available_balance}}."

Conditional sections

Templates support conditional rendering with {{#if}}...{{/if}}:

RESPOND: |
  Transfer complete.
  {{#if fx_rate}}Exchange rate: {{fx_rate}}{{/if}}
  Estimated arrival: {{estimated_arrival}}.

Function calls in templates

You can call built-in functions within template strings:

SET:
  formatted_balance = FORMAT_CURRENCY(available_balance, "USD")
RESPOND: "Your balance is {{formatted_balance}}."

Built-in function reference

ABL provides 36 built-in functions organized into seven categories (plus the CEL-only content-analysis helpers described below). All functions are called with FUNCTION_NAME(arg1, arg2, ...) syntax. Function names are uppercase.

Math functions

Function	Signature	Description	Example
`ADD`	`ADD(a, b) -> number`	Add two numbers.	`ADD(2, 3)` returns `5`
`SUB`	`SUB(a, b) -> number`	Subtract b from a.	`SUB(10, 3)` returns `7`
`MUL`	`MUL(a, b) -> number`	Multiply two numbers.	`MUL(4, 5)` returns `20`
`DIV`	`DIV(a, b) -> number`	Divide a by b. Returns `null` for division by zero.	`DIV(10, 2)` returns `5`
`ROUND`	`ROUND(n, decimals?) -> number`	Round to specified decimal places. Default: 0.	`ROUND(3.14159, 2)` returns `3.14`
`ABS`	`ABS(n) -> number`	Absolute value.	`ABS(-5)` returns `5`
`MIN`	`MIN(a, b) -> number`	Return the smaller of two numbers.	`MIN(3, 7)` returns `3`
`MAX`	`MAX(a, b) -> number`	Return the larger of two numbers.	`MAX(3, 7)` returns `7`

Math functions coerce string arguments to numbers automatically: ADD("2", "3") returns 5.

String functions

Function	Signature	Description	Example
`UPPER`	`UPPER(s) -> string`	Convert to uppercase.	`UPPER("hello")` returns `"HELLO"`
`LOWER`	`LOWER(s) -> string`	Convert to lowercase.	`LOWER("HELLO")` returns `"hello"`
`TRIM`	`TRIM(s) -> string`	Strip leading/trailing whitespace.	`TRIM(" hi ")` returns `"hi"`
`SUBSTRING`	`SUBSTRING(s, start, end?) -> string`	Extract a substring.	`SUBSTRING("hello", 0, 3)` returns `"hel"`
`REPLACE`	`REPLACE(s, find, repl) -> string`	Replace all occurrences.	`REPLACE("a,b,c", ",", "-")` returns `"a-b-c"`
`SPLIT`	`SPLIT(s, delimiter) -> string[]`	Split string into array.	`SPLIT("a,b,c", ",")` returns `["a","b","c"]`
`JOIN`	`JOIN(arr, delimiter) -> string`	Join array into string.	`JOIN(["a","b"], ", ")` returns `"a, b"`
`PAD_START`	`PAD_START(s, length, char?) -> string`	Left-pad to specified length.	`PAD_START("42", 6, "0")` returns `"000042"`
`PAD_END`	`PAD_END(s, length, char?) -> string`	Right-pad to specified length.	`PAD_END("42", 6, "0")` returns `"420000"`
`REPEAT`	`REPEAT(s, count) -> string`	Repeat string N times.	`REPEAT("", 4)` returns `"***"`

The string functions gracefully handle null and undefined and return an empty string: UPPER(null) returns "". To prevent memory issues, the limit on string output is 100,000 characters.

Formatting functions

Function	Signature	Description	Example
`MASK`	`MASK(s, pattern, char?) -> string`	Mask a string. See Mask Patterns below.	`MASK("4111111111111111", "last4")` returns `"************1111"`
`FORMAT_CURRENCY`	`FORMAT_CURRENCY(n, currency, locale?) -> string`	Format a number as currency.	`FORMAT_CURRENCY(1234.5, "USD")` returns `"$1,234.50"`
`FORMAT_DATE`	`FORMAT_DATE(d, format, tz?) -> string`	Format a date string.	`FORMAT_DATE("2024-03-15T10:30:00Z", "YYYY-MM-DD")` returns `"2024-03-15"`
`ORDINAL`	`ORDINAL(n) -> string`	Convert number to ordinal string.	`ORDINAL(1)` returns `"1st"`, `ORDINAL(22)` returns `"22nd"`

The mask patterns are explained below.

Pattern	Behavior	Example result
`last4`	Mask all characters except the last 4.	`"************1111"`
`first4`	Mask all characters except the first 4.	`"4111************"`
`N*N`	Show N chars at start, mask middle, show N at end.	`MASK(s, "4*4")` shows 4+4

The default mask character is *. Pass a third argument to use a different character: MASK(ssn, "last4", "x"). The date format uses the following notations:

Token	Description	Example
`YYYY`	Four-digit year	`2024`
`MM`	Two-digit month	`03`
`DD`	Two-digit day	`15`
`HH`	Two-digit hour (24h)	`10`
`mm`	Two-digit minute	`30`
`ss`	Two-digit second	`00`

Example: FORMAT_DATE("2024-03-15T10:30:00Z", "YYYY-MM-DD HH:mm") returns "2024-03-15 10:30". FORMAT_DATE formats in UTC by default — a date-time string without an explicit offset is interpreted as UTC, so the output is deterministic regardless of where the runtime executes. Pass an optional IANA timezone name as the third argument to format in that zone instead:

FORMAT_DATE("2024-03-15T10:30:00Z", "YYYY-MM-DD HH:mm", "America/New_York")  # "2024-03-15 06:30"

An unrecognized timezone falls back to UTC.

Type checking and coercion functions

Function	Signature	Description	Example
`IS_ARRAY`	`IS_ARRAY(x) -> boolean`	True if the value is an array.	`IS_ARRAY([1,2])` returns `true`
`IS_NUMBER`	`IS_NUMBER(x) -> boolean`	True if the value is a number (not NaN).	`IS_NUMBER(42)` returns `true`
`IS_STRING`	`IS_STRING(x) -> boolean`	True if the value is a string.	`IS_STRING("hi")` returns `true`
`TO_NUMBER`	`TO_NUMBER(x) -> number`	null	Convert to number. Returns `null` if conversion fails. `TO_NUMBER("42")` returns `42`
`TO_STRING`	`TO_STRING(x) -> string`	Convert to string. Returns `""` for null/undefined.	`TO_STRING(42)` returns `"42"`

Array functions

Function	Signature	Description	Example
`LENGTH`	`LENGTH(x) -> number`	Array length or string length. Returns 0 for other types.	`LENGTH([1,2,3])` returns `3`
`ARRAY_FIND`	`ARRAY_FIND(arr, field, value) -> object`	null	Find first element where `field == value`. `ARRAY_FIND(users, "id", 42)` returns the matching object
`ARRAY_FIND_INDEX`	`ARRAY_FIND_INDEX(arr, field, value) -> number`	Find index of first match. Returns -1 if not found.	`ARRAY_FIND_INDEX(items, "type", "b")` returns the index

Object functions

Function	Signature	Description	Example
`OBJECT_KEYS`	`OBJECT_KEYS(obj) -> string[]`	Return array of object keys.	`OBJECT_KEYS({a:1, b:2})` returns `["a","b"]`
`OBJECT_VALUES`	`OBJECT_VALUES(obj) -> any[]`	Return array of object values.	`OBJECT_VALUES({a:1, b:2})` returns `[1, 2]`
`OBJECT_MERGE`	`OBJECT_MERGE(obj1, obj2, ...) -> object`	Merge objects. Right-side values win on conflict.	`OBJECT_MERGE({a:1}, {b:2})` returns `{a:1, b:2}`

OBJECT_KEYS and OBJECT_VALUES return an empty array for non-object inputs (null, arrays, strings). OBJECT_MERGE accepts any number of arguments and skips non-object values.

Utility functions

Function	Signature	Description	Example
`COALESCE`	`COALESCE(a, b, ...) -> any`	Return the first non-null, non-undefined value. Returns `null` if all arguments are null.	`COALESCE(null, undefined, "hello")` returns `"hello"`
`NOW`	`NOW() -> string`	Return the current timestamp as an ISO 8601 string.	`NOW()` returns `"2024-03-15T10:30:00.000Z"`
`UNIQUE_ID`	`UNIQUE_ID(length?) -> string`	Generate a random alphanumeric string. Default length: 6.	`UNIQUE_ID(12)` returns `"aB3kM9pQ2xLw"`

COALESCE considers 0 and false as valid (non-null) values: COALESCE(0, "fallback") returns 0. UNIQUE_ID generates a random alphanumeric string suitable for reference numbers. It is not cryptographically secure — do not use it for tokens or secrets.

Content-analysis functions (CEL guardrails)

CEL-based guardrail checks have access to an additional abl.* namespace of content-analysis helpers:

Function	Description
`abl.contains_pii(text)`	True if the text contains PII.
`abl.detect_pii(text)`	Structured PII detection result.
`abl.redact_pii(text)`	Returns the text with PII redacted.
`abl.matches_pattern(text, pattern)`	Regex match (RE2-backed).
`abl.not_matches_pattern(text, pattern)`	Negation of `matches_pattern`.
`abl.word_count(text)`	Word count.
`abl.sentence_count(text)`	Sentence count.
`abl.contains_url(text)`	True if the text contains a URL.
`abl.contains_email(text)`	True if the text contains an email address.
`abl.contains_code(text)`	True if the text contains a fenced code block.
`abl.pii_equal(left, right)`	True if two PII-vault tokens hold the same underlying value. See below.

In CEL expressions the core functions above are also available under the abl. namespace with lowercase names (e.g. abl.upper(x)), and CEL-native operators (&&, ||, !, %, in, ternary ? :) and macros (size(), has()) can be used.

abl.pii_equal(left, right) compares two values without ever exposing the underlying plaintext to the expression — both left and right must be live PII-vault tokens (the opaque form a PII-classified value takes once captured, e.g. via a sensitive: true GATHER field), and the comparison happens inside the vault itself. Values are canonicalized before comparing (email lowercased/trimmed, phone/SSN/credit-card digits-only, etc.), so abl.pii_equal(session.data.values.email, caller_provided_email) matches Member@Example.com against member@example.com.

CHECK: abl.pii_equal(session.data.values.email, caller_provided_email)
ON_FAIL: identity_mismatch

If either operand isn’t a live vault token for the same PII type — missing, expired, or a plain string — abl.pii_equal throws rather than returning false. This is deliberate: silently returning false on a fault would make !abl.pii_equal(x, y) evaluate true on a comparison that couldn’t actually be performed. Guard against this with IS SET checks on both operands before comparing, or route the resulting evaluation error through your usual error handling.

Nested function calls

Functions can be nested as arguments to other functions:

SET:
  result = ADD(MUL(2, 3), SUB(10, 4))     # Returns 12
  name = UPPER(TRIM("  hello  "))           # Returns "HELLO"
  fallback = COALESCE(user.lastName, "Guest")

Nesting is limited to a maximum depth of 32 to prevent stack overflow.

Using expressions in ABL

In conditions (WHEN, CHECK, constraint rules)

WHEN: user.age >= 18 AND user.verified == true
CHECK: amount <= available_balance
- REQUIRE sanctions_clear == true

In SET assignments

SET:
  balance_formatted = FORMAT_CURRENCY(available_balance, "USD")
  wire_reference = UNIQUE_ID(12)
  greeting = COALESCE(user.name, "valued customer")

In template interpolation

RESPOND: "Hello, {{customer_name}}! Balance: {{FORMAT_CURRENCY(available_balance, 'USD')}}."

In TRANSFORM pipelines

TRANSFORM:
  SOURCE: search_results
  AS: item
  INTO: filtered_results
  FILTER: item.price <= budget AND item.available == true
  MAP:
    name: item.hotel_name
    price: FORMAT_CURRENCY(item.price, "USD")
  SORT_BY: price ASC
  LIMIT: 5

Type coercion rules

The evaluator applies these coercion rules during expression evaluation:

Context	Rule
Equality (`==`)	null/undefined == null/undefined is true. Strings compared case-sensitively. Numbers parsed from strings.
Inequality (`!=`)	If either side is undefined/null, returns true.
Numeric (`>`, `<`, etc.)	Strings parsed to numbers. Booleans become 0/1. Arrays become length. Undefined becomes 0.
Truthiness (bare variable)	`false`, `0`, `""`, `"false"`, `null`, `undefined`, empty arrays, empty objects are falsy. Everything else is truthy.
IS SET / IS NOT SET	Checks for null/undefined only. Empty string IS SET.

Related articles:

Rich content — voice configuration, format-specific output, carousels, interactive actions, and templates
Memory and constraints — condition expressions in constraint rules, variable paths and session context
Multi-Agent and supervisor — condition syntax for WHEN clauses in routing/escalation
Data Types and utilities — types used in function signatures, lookup validation functions

​Expression syntax

​Comparison operators

​Logical operators

​Unary operators

​Operator precedence

​Variable paths and dot notation

​Path resolution rules

​Template strings

​Conditional sections

​Function calls in templates

​Built-in function reference

​Math functions

​String functions

​Formatting functions

​Type checking and coercion functions

​Array functions

​Object functions

​Utility functions

​Content-analysis functions (CEL guardrails)

​Nested function calls

​Using expressions in ABL

​In conditions (WHEN, CHECK, constraint rules)

​In SET assignments

​In template interpolation

​In TRANSFORM pipelines

​Type coercion rules

Expression syntax

Comparison operators

Logical operators

Unary operators

Operator precedence

Variable paths and dot notation

Path resolution rules

Template strings

Conditional sections

Function calls in templates

Built-in function reference

Math functions

String functions

Formatting functions

Type checking and coercion functions

Array functions

Object functions

Utility functions

Content-analysis functions (CEL guardrails)

Nested function calls

Using expressions in ABL

In conditions (WHEN, CHECK, constraint rules)

In SET assignments

In template interpolation

In TRANSFORM pipelines

Type coercion rules