FEEL Reference

FEEL (Friendly Enough Expression Language) is the standard expression language defined by the OMG for use in DMN and BPMN. Expressions in Priostack - sequence-flow conditions, DMN input expressions and output entries, CMMN sentries - use FEEL.

The engine implements a subset of FEEL, and this page lists what it evaluates. An expression outside that subset has no answer: in a gateway condition the instance goes to INCIDENT, and in a DMN cell the deploy refuses it.

Types

Arithmetic Operators

// Basic arithmetic
1 + 2          // => 3
10 - 3         // => 7
4 * 5          // => 20
10 / 3         // => 3.3333...
// there is no exponent operator: ** is not evaluated

// With variables
amount * 1.2   // apply 20% markup
(price - cost) / cost * 100  // percentage margin

// Duration arithmetic
date("2026-05-01") + duration("P30D")  // => date("2026-05-31")
now() - duration("PT1H")               // one hour ago

Comparison Operators

amount = 100        // equal
amount != 100       // not equal
amount < 100        // less than
amount <= 100       // less than or equal
amount > 100        // greater than
amount >= 100       // greater than or equal

// Range expressions (shorthand for comparisons)
amount in [0..100]  // 0 <= amount <= 100 (inclusive)
amount in ]0..100[  // 0 < amount < 100 (exclusive)
amount in [0..100)  // 0 <= amount < 100 (mixed)

// Membership test
status in ("pending", "review", "approved")  // any of these values

A range opening with (, such as (0..100), and a square-bracket list, such as ["pending", "review"], are not accepted after in today: write an exclusive bound with ] or [ turned outward, and a list of values in parentheses.

Logical Operators

true and false     // => false
true or false      // => true
not(true)          // => false

// Compound conditions
amount > 0 and status = "approved"
(tier = "gold" or tier = "platinum") and amount > 100

String Functions

Not implemented: trim, string join, split.

Date and Time Functions

Not implemented: day of week, day of year, month of year, week of year.

// Check if a date is at the weekend (d holds a date such as "2026-10-03")
d.weekday >= 6  // => true on Saturday and Sunday

// Calculate age from birthdate, as a value
years and months duration(date("1990-01-15"), today()).years  // => age in years

// Check if overdue
dueDate < today()  // => true if past due

Compare a property read from a variable, as in d.weekday >= 6. A property read directly off a function call works as a value, but comparing it does not work today: years and months duration(date(birth), today()).years >= 18 answers false, and has no answer in a gateway condition.

List Functions

Not implemented: append, concatenate, insert before, remove, reverse, index of, distinct values, flatten, sort.

Filter and Quantifier Expressions

// Filter: keep items matching a condition
items[price > 100]            // all items where price > 100
items[status = "approved"]    // all approved items

// Some/Every quantifiers
some x in items satisfies x.price > 100    // true if any item has price > 100
every x in items satisfies x.valid = true  // true if all items are valid

// For expression: transform a list variable
for item in items return item.name        // list of names
// iterating over a range (for i in 1..5) is not supported

// Access first element
items[1].name    // name of first item (1-based)
items[-1].name   // name of last item

Context Operations

// Create a context
{ name: "Alice", age: 30, address: { city: "Paris" } }

// Access fields
person.name           // => "Alice"
person.address.city   // => "Paris"

// Not implemented: context merge, context(), get entries, get value

Conditional Expressions

// if/then/else
if amount > 1000 then "high" else "low"

// Combine conditions instead of nesting: an if inside another if is not
// supported. Use a decision table for more than two branches.
if tier = "gold" and amount > 500 then 15 else 0

// Guard against a missing value: customer.email when customer holds a value, null otherwise
if customer != null then customer.email else null

Function Definitions

Not supported: the engine evaluates neither function literals nor functions defined inside a context. Put reusable logic in a decision table, or compute it in a worker.

Numeric Functions

min, max and sum also take separate arguments: sum(1, 2, 3). Not implemented: round up, round down, decimal, product, mean, median.

Usage in DMN Decision Tables

In decision table input cells, FEEL expressions are used as unary tests against the input column value:

Output cells contain FEEL expressions, within the subset above:

// Output: fixed string
"approved"

// Output: conditional based on other variables
if amount > 100000 then "escalate" else "approve"

// Output: computed value
amount * interestRate

Usage in BPMN Gateways

In BPMN sequence flows from exclusive gateways, add a <conditionExpression>:

<sequenceFlow id="to-approve" sourceRef="gw1" targetRef="approve-task">
  <conditionExpression>= riskLevel = "LOW" or (riskLevel = "MEDIUM" and amount &lt; 50000)</conditionExpression>
</sequenceFlow>

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