Friendly enough expression language (FEEL) for the purpose of giving standard executable semantics to many kinds of expressions in decision model has the following features;

Side-effect free
Simple data model with numbers, dates, strings, lists and contexts
Simple syntax designed for a wide audience
Three-valued logic (true, false, null)

Data Types

FEEL supports the following datatypes:

number
string
boolean
days and time duration
years and months duration
time
date and time
list
context

Duration and date/time datatypes have no literal syntax. They must be constructed from a string representation using a built-in function (see conversion functions)

Contexts, Lists, Qualified Names

A context is a map of key-value pairs called context entries, and is written using curly braces to delimit the context, commas to separate the entries, and a colon to separate key and value. The key can be a string or a name. The value is an expression.

A list is written using square brackets to delimit the list, and commas to separate the list items. A singleton list is equal to its single item, Example "[e]=e" for all FEEL expressions.

Contexts and lists can reference other contexts and lists, giving rise to a directed acyclic graph. Naming is path based. The qualified name (QN) of a context entry is of the form "N1.N2 ... Nn" where N1 is the name of an in-scope context.

Nested lists encountered in the interpretation of N1.N2 ... Nn are preserved. For example,

    [{a: [{b: 1}, {b: [2.1, 2.2]}]}, {a: [{b: 3}, {b: 4}, {b: 5}]}].a.b =
    [[{b: 1}, {b: [2.1, 2.2]}], [{b: 3}, {b: 4}, {b: 5}]].b =
    [[1, [2.1, 2.1]],[ 3, 4, 5]]

Nested lists can be flattened using the flatten() built-in function.

Literal and Data Type Semantics

Equality

In general, the values to be compared must be of the same kind. For example; FEEL("1" = 1) = null

data type	e1 = e2
list	lists must be same length, and e1[n] = e2[n] must be equal
context	context must be same set of keys and every e1.key = e2.key must be equal
range	range start and end points must be same
number	value of numbers must be equal
string	value of string must be equals with case sensitivity
date	all date components must be equal
date and time	all date and time components must be equal
time	all time components must be equal
days and time duration	value of duration must be equal
years and months duration	value of duration must be equal
boolean	both e1 and e2 must be true or false

number

Feel numbers based on decimal format, there is no integer or float data types.

Literals consist of base 10 digits and an optional decimal point. –INF, +INF, and NaN literals are not supported. There is no distinction between -0 and 0. The number(from, grouping separator, decimal separator) built-in function supports a richer literal format. For example, FEEL(number("1.000.000,01", ".", ",")) = 1000000.01

There is no value for NaN, positiveInfinity, or negativeInfinity. Use null instead.

string

Literal strings can be double-quoted or single quoted sequence of characters. e.g. "abc" All strings compared as UTF-8 encoding.

boolean

Boolean literals are true and false.

time

Feel does not have time literals although time values can be expressed using a string literal and time built-in function.

Time values also have optional time zone offset. If no time zone offset specified, time is interpreted as local time of day.

Time data type has also provides an context of sequence of numbers for the hour, minute, second, and an optional time offset.

date

Feel does not have time literals although time values can be expressed using a string literal and date built-in function.

Date values has no time zone offset and interpreted as UTC time zone.

Date data type has also provides an context of sequence of numbers for the year, month, day of month.

date time

Feel does not have time literals although time values can be expressed using a string literal and date time built-in function.

Date time also have optional time zone offset. If no time zone offset specified, time is interpreted as UTC time zone.

Date time data type has also provides an context of sequence of numbers for the year, month, day, hour, minute, second, and optional time offset.

days and time duration

Feel does not have time literals although time values can be expressed using a string literal and days and time duration built-in function. Duration format expressed in ISO 8601 duration syntax.

Days and time duration data type has also provides an context of sequence of numbers for the days, hours, minutes, and seconds of duration and normalized such that the sum of these numbers is minimized. For example; FEEL(duration("P0DT25H")) = P1DT1H

years and months duration

Feel does not have time literals although time values can be expressed using a string literal and years and months duration built-in function. Duration format expressed in ISO 8601 duration syntax.

Days and time duration data type has also provides an context of sequence of numbers for the years and months of duration and normalized such that the sum of these numbers is minimized. For example; FEEL(duration("P0Y13M")) = P1Y1M

Lists and filters

Lists are immutable and may be nested. First element of list can be accessed using L[1] and last element accessed using L[-1]. If no element exists in list then L[n] = null.

Lists can be filtered with a boolean expression in square brackets. The expression in square brackets can reference a list element using name "item". If list entries is a context, item entries may be referenced within filter expression without item prefix. For example;

    [1, 2, 3, 4][item > 2] = [3, 4]
    [{x:1, y:2}, {x:2, y:3}][x=1] = {x:1, y:2}

For convenience a selection using "." operator with a list of contexts on its left hand side returns a list of selections. For example;

    [{x:1, y:2}, {x:2, y:3}].y = [2,3]

Context

Context is a collection of key and expression pairs called context entries. Keys are mapped to string values. The syntax for selecting value of context entry named key1 from context1 is "context1.key1"

To retrieve a list of key,value pairs from a context m, the following built-in function may be used: get entries(m).

Range

Feel supports the compact syntax for range of values.

Negation

Negation is performed with builtin not function. Semantics of negation is;

a	not(a)
true	false
false	true
otherwise	null

Binary logic

Binary logic can be expressed with "and" and "or" keywords. Binary logic semantics;

a	b	a and b	a or b
true	true	true	true
true	false	false	true
true	otherwise	null	true
false	true	false	true
false	false	false	false
false	otherwise	false	null
otherwise	otherwise	null	null

Xml Data Mapping

FEEL supports the xml data context in contexts. Xml namespaces are not supported but elements can be accessed with prefix. All xml values are interpreted as string values.

XML	context entry	Remarks
<e />	e : null	empty element mapped to null value.
<n:e />	n$e : null	namespaces are ignored and prefix can be used to access entry.
<e>v</e>	e : "v"	single element with value
<e>v1</e><e>v2</e>	e : ["v1","v2"]	repeating element with value
<e a="v">v1</e>	e$a : "v" e : "v1"	attributes are prefixed with @ element value accessed with name
<e a="v">v1 <c>v1</c> </e>	e$a : "v", e.c : "v1"	attributes are prefixed with @ childs accessed with name

Builtin Functions

To promote interoperability, FEEL includes a library of built-in functions. The syntax and semantics of the built-ins are required for a conformant FEEL implementation.

Conversion Functions

FEEL supports many conversions between values of different types. Of particular importance is the conversion from strings to dates, times, and durations. There is no literal representation for date, time, or duration. Also, formatted numbers such as 1,000.00 must be converted from a string by specifying the grouping separator and the decimal separator.

Name and Parameters	Parameter	Description	Example
date(from)	date string	convert from to a date	date("2012-12-25") – date("2012-12-24") = duration("P1D")
date(from)	date and time	convert from to a date (set time components to null)	date(date and time("2012-12-25T11:00:00Z")) = date("2012-12-25")
date(year, month, day)	year, month, day are numbers	creates a date from year, month, day component values	date(2012, 12, 25) = date("2012-12-25")
date and time(date, time)	date is a date or date time; time is a time	creates a date time from the given date (ignoring any time component) and the given time	date and time ("2012-12-24T23:59:00") = date and time (date("2012-12-24”), time(“T23:59:00"))
date and time(from)	date time string	convert from to a date and time	date and time("2012-12-24T23:59:00") + duration("PT1M") = date and time("2012-12- 25T00:00:00")
time(from)	time string	convert from to time	time("23:59:00z") + duration("PT2M") = time("00:01:00@Etc/UTC")
time(from)	time, date and time	convert from to time (ignoring date components)	time(date and time("2012-12-25T11:00:00Z")) = time("11:00:00Z")
time(hour, minute, second, offset)	hour, minute, second, are numbers, offset is a days and time duration, or null	creates a time from the given component values	time(“T23:59:00z") = time(23, 59, 0, duration(“PT0H”))
number(from, grouping separator, decimal separator)	string, string, string	convert from to a number	number("1 000,0", " ", ",") = number("1,000.0", ",", ".")
string(from)	non-null	convert from to a string	string(1.1) = "1.1" string(null) = null
duration(from)	duration string	convert from to a days and time or years and months duration	date and time("2012-12-24T23:59:00") - date and time("2012-12-22T03:45:00") = duration("P2DT20H14M") duration("P2Y2M") = duration("P26M")
years and months duration(from, to)	both are date and time	return years and months duration between from and to	years and months duration( date("2011-12-22"), date("2013-08-24") ) = duration("P1Y8M")

Boolean Functions

Name and Parameters

Parameter

Description

Example

boolean(from)

string

boolean conversion

boolean("true") = true

boolean("false") = false

boolean(true) = true

not(negand)

boolean

logical negation

not(true) = false

not(null) = null

String Functions

Name and Parameters	Parameter	Description	Example
substring(string, start position, length?)	string, number	return length (or all) characters in string, starting at start position. 1st position is 1, last position is -1	substring("foobar",3) = "obar" substring("foobar",3,3) = "oba" substring("foobar", -2, 1) = "a"
string length(string)	string	return length of string	string length("foo") = 3
upper case(string)	string	return uppercased string	upper case("aBc4") = "ABC4"
lower case(string)	string	return lowercased string	lower case("aBc4") = "abc4"
substring before (string, match)	string, string	return substring of string before the match in string	substring before("foobar", "bar") = "foo" substring before("foobar", "xyz") = ""
substring after (string, match)	string, string	return substring of string after the match in string	substring after("foobar", "ob") = "ar" substring after("", "a") = ""
replace(input, pattern, replacement, flags?)	string	regular expression pattern matching and replacement	replace("abcd", "(ab)\|(a)", "[1=$1][2=$2]") = "[1=ab][2=]cd"
contains(string, match)	string	does the string contain the match ?	contains("foobar", "of") = false
starts with(string, match)	string	does the string start with the match ?	starts with("foobar", "fo") = true
ends with(string, match)	string	does the string end with the match ?	ends with("foobar", "r") = true
matches(input, pattern, flags?)	string	does the input match the regexp pattern ?	matches("foobar", "^fo*b") = true

List Functions

Name and Parameters	Parameter	Description	Example
list contains(list, element)	list, any element of the semantic domain including null	does the list contain the element ?	list contains([1,2,3], 2) = true
count(list)	list	return size of list	count([1,2,3]) = 3
min(list) min(c1,..., cN), N >1 max(list) max(c1,..., cN), N >1	(list of) comparable items	return minimum item return maximum item	min([1,2,3]) = 1 min(1,2,3) = 1 max([1,2,3]) = 3 max(1,2,3) = 3
sum(list) sum(n1,..., nN), N >1	(list of) numbers	return sum of numbers	sum([1,2,3]) = 6 sum(1,2,3) = 6
mean(list) mean(n1,..., nN), N >1	(list of) numbers	return arithmetic mean (average) of numbers	mean([1,2,3]) = 2 mean(1,2,3) = 2
and(list) and(b1,..., bN), N >1	(list of) Boolean items	return false if any item is false, else true if all items are true, else null	and([false,null,true]) = false and(false,null,true) = false and([]) = true and(0) = null
or(list) or(b1,..., bN), N >1	(list of) Boolean items	return true if any item is true, else false if all items are false, else null	or([false,null,true]) = true or(false,null,true) = true or([]) = false or(0) = null
sublist(list, start position, length?)	list, number1, number2	return list of length (or all) elements of list, starting with list[start position]. 1st position is 1, last position is -1	sublist([1,2,3], 1, 2) = [2]
append(list, item...)	list, any element including null	return new list with items appended	append([1], 2, 3) = [1,2,3]
concatenate(list...)	list	return new list that is a concatenation of the arguments	concatenate([1,2],[3]) = [1,2,3]
insert before(list, position, newItem)	list, number1, any element including null	return new list with newItem inserted at position	insert before([1,3],1,2) = [1,2,3]
remove(list, position)	list, number1	list with item at position removed	remove([1,2,3], 2) = [1,3]
reverse(list)	list	reverse the list	reverse([1,2,3]) = [3,2,1]
index of(list, match)	list, any element including null	return ascending list of list positions containing match	index of([1,2,3,2],2) = [2,4]
union(list...)	list	concatenate with duplicate removal	union([1,2],[2,3]) = [1,2,3]
distinct values(list)	list	duplicate removal	distinct values([1,2,3,2,1] = [1,2,3]
flatten(list)	list	flatten nested lists	flatten([[1,2],[[3]], 4]) = [1,2,3,4]

Numeric functions

Name and Parameters	Parameter	Description	Example
decimal(n, scale)	number, number1	return n with given scale	decimal(1/3, 2) = .33 decimal(1.5, 0) = 2 decimal(2.5, 0) = 2
floor(n)	number	return greatest integer <= n	floor(1.5) = 1 floor(-1.5) = -2
ceiling(n)	number	return smallest integer >= n	ceiling(1.5) = 2 ceiling(-1.5) = -1