FEEL Syntax

Friendly Enough Expression Language (FEEL) is standardized by OMG. It is a side-effect-free expression language designed to be easy for business professionals to read and write.

Data Types

FEEL allows you to work with rich data types.

Primitive Types

Type	Description	Examples
Number	High-precision decimal numbers. Supports scientific notation.	10, -5.2, 1.5e3
String	Text enclosed in double quotes. Special characters can be escaped.	"Hello World", "Bob's ID", "\u0009"
Boolean	Logical true or false.	true, false
Null	Represents a missing or unknown value.	null

Temporal Types

FEEL has first-class support for dates and times.

Date: date("2023-12-31") Time: time("14:30:00") or time("14:30:00@Europe/Paris") Date and Time: date and time("2023-12-31T14:30:00") Duration: Day-Time: duration("P2DT5H") (2 Days, 5 Hours) Year-Month: duration("P1Y6M") (1 Year, 6 Months)

Composite Types

Lists

Ordered collections of values. Elements can be of any type, including other lists.

[1, 2, 3, 4]
["Red", "Green", "Blue"]
[{x:1}, {x:2}]

Contexts

A set of key-value pairs, similar to a JSON object or a Map.

{
  "Customer Name": "Alice",
  "Age": 30,
  "Address": {
    "City": "New York",
    "Zip": "10001"
  }
}

Expressions

Arithmetic

Standard mathematical operations are supported.

10 + 5      // 15
10 - 2      // 8
10 * 3      // 30
20 / 4      // 5
2 ** 3      // 8 (Exponentiation)
(10 + 2) * 3 // 36

Boolean Logic

FEEL uses three-valued logic (true, false, null).

• AND: true and true -> true
• OR: true or false -> true
• Equality: Price = 100
• Inequality: Price != 100
• Comparison: Price > 50, Price <= 200

Conditional (If-Then-Else)

Evaluates a condition and returns one of two values.

if Age >= 18 then "Adult" else "Minor"

Flow Control

For Loops

Iterate over lists to transform primitive values or objects.

for x in [1, 2, 3] return x * 2  // [2, 4, 6]

Quantified Expressions

Check if some or every element in a list satisfies a condition.

some price in [10, 20, 30] satisfies price > 25  // true
every price in [10, 20, 30] satisfies price > 5   // true

Unary Tests

Unary tests are expressions that test a single input value (implicit ?). They are primarily used in Decision Tables (in the input entries) or with the in operator.

Test Type	Syntax	Meaning
Literal	"High"	The input MUST match "High"
Numeric	10	The input MUST be 10
Comparison	< 10	The input MUST be less than 10
Interval	[1..10]	Inclusive: 1 <= input <= 10
Interval	(1..10)	Exclusive: 1 < input < 10
Negation	not(10)	Any value EXCEPT 10
List	1, 2, 3	Input matches any item (OR logic)
Generalized	not(1, 2)	Neither 1 nor 2

Built-in Functions

FEEL includes a standard library of functions.

• count([1, 2, 3]) -> 3
• sum([10, 20]) -> 30
• string length("foo") -> 3
• upper case("hello") -> "HELLO"
• contains("foobar", "bar") -> true

Comments

Code can be annotated with comments.

// This is a single line comment
10 + 10

/*
 This is a
 block comment
*/