FEEL Reference

FEEL (Friendly Enough Expression Language) is the standard expression language defined by the OMG for use in DMN and BPMN. All expressions in Priostack — conditions, output expressions, variable mappings — use FEEL.

Types

Arithmetic Operators

// Basic arithmetic
1 + 2          // => 3
10 - 3         // => 7
4 * 5          // => 20
10 / 3         // => 3.3333...
10 ** 2        // => 100  (exponentiation)

// 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

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

Date and Time Functions

// Check if date is a weekday
day of week(today()) in ["Saturday", "Sunday"]  // => true if weekend

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

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

List Functions

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
for item in items return item.name        // list of names
for i in 1..5 return i * i               // [1, 4, 9, 16, 25]

// 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"

// Merge contexts
context merge({ a: 1 }, { b: 2 })  // => { a: 1, b: 2 }

// Context from list of pairs
context([["a", 1], ["b", 2]])  // => { a: 1, b: 2 }

// Get keys and values
get entries({ a: 1, b: 2 })   // => [{key:"a",value:1},{key:"b",value:2}]
get value({ a: 1 }, "a")      // => 1

Conditional Expressions

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

// Nested conditions
if tier = "gold" then
  if amount > 500 then 15 else 10
else
  if amount > 200 then 8 else 5

// Null-safe access (returns null instead of error)
if customer != null then customer.email else null

Function Definitions

// Define and immediately call a function
(function(x, y) x + y)(3, 4)  // => 7

// Named function (in DMN context or FEEL context)
{
  discount: function(tier, amount)
    if tier = "gold" and amount > 500 then 0.15
    else if tier = "gold" then 0.10
    else 0,
  finalPrice: amount * (1 - discount(customerTier, amount))
}