Lists

Lists in RuLA are ordered collections of values. They can contain any type of value: strings, numbers, other lists, or dictionaries.

Creating Lists

Use square brackets with comma-separated values:

['apple', 'banana', 'cherry']           # List of strings
[1, 2, 3, 4, 5]                          # List of numbers
[]                                       # Empty list
['text', 42, {'key': 'value'}]          # Mixed types

Accessing List Elements

Access elements by index (0-based):

fruits = ['apple', 'banana', 'cherry']
fruits[0]           # Returns 'apple'
fruits[2]           # Returns 'cherry'

List Manipulation

Adding Elements

APPEND([1, 2], 3)             # Returns [1, 2, 3]
CONCAT([1, 2], [3, 4])        # Concatenation: [1, 2, 3, 4]

Filtering

numbers = [1, 2, 3, 4, 5]
FILTER(numbers, x => x > 3)             # Returns [4, 5]
FILTER_FALSE(true, false, true, false)  # Returns [true, true]

Transforming (Mapping)

numbers = [1, 2, 3]
MAP(numbers, x => x * 2)        # Returns [2, 4, 6]

Sorting and Reversing

SORT([3, 1, 2])                 # Returns [1, 2, 3]
SORT(['banana', 'apple'])       # Returns ['apple', 'banana']
REVERSE([1, 2, 3])              # Returns [3, 2, 1]

Getting Unique Elements

SET([1, 2, 2, 3, 3, 3])         # Returns [1, 2, 3]

Flattening Nested Lists

FLATTEN([[1, 2], [3, 4]])       # Returns [1, 2, 3, 4]

Useful List Functions

Function	Description	Example
COUNT	Number of elements	COUNT([1, 2, 3]) → 3
SORT	Sort in ascending order	SORT([3, 1, 2]) → [1, 2, 3]
REVERSE	Reverse the order	REVERSE([1, 2, 3]) → [3, 2, 1]
FIRST_ELEMENT	Get first element	FIRST_ELEMENT([1, 2, 3]) → 1
LAST_ELEMENT	Get last element	LAST_ELEMENT([1, 2, 3]) → 3
APPEND	Add element to end	APPEND([1, 2], 3) → [1, 2, 3]
INDEX_OF	Find position (0-based)	INDEX_OF(['a', 'b'], 'b') → 1
SET	Remove duplicates	SET([1, 1, 2]) → [1, 2]
FLATTEN	Flatten one level	FLATTEN([[1], [2]]) → [1, 2]
UNION(list1, list2)	Combine unique elements	UNION([1, 2], [2, 3]) → [1, 2, 3]
INTERSECTION	Common elements	INTERSECTION([1, 2], [2, 3]) → [2]
SET_DIFFERENCE	Elements in list1 not in list2	SET_DIFFERENCE([1, 2], [2, 3]) → [1]
SUM	Sum of numbers	SUM([1, 2, 3]) → 6
AVG	Average of numbers	AVG([1, 2, 3]) → 2
MIN	Minimum value	MIN([3, 1, 2]) → 1
MAX	Maximum value	MAX([3, 1, 2]) → 3
CONCAT	Join all strings	CONCAT(['a', 'b']) → "ab"
JOIN	Join with separator	JOIN(['a', 'b'], '-') → "a-b"
MAP	Transform each element	MAP([1, 2], x => x * 2) → [2, 4]
FILTER	Keep matching elements	FILTER([1, 2, 3], x => x > 1) → [2, 3]
ALL	All values true?	ALL([true, true, false]) → False
ANY	Any value true?	ANY([true, true, false]) → True
SOME	Any value true? (alias for ANY)	SOME([true, false]) → True
CUSTOM_MAX	Max element ranked by an ordering list	CUSTOM_MAX([red, green], [green, red]) → red

Checking List Contents

fruits = ['apple', 'banana']

fruits contains 'apple'                  # True
fruits contains any ['apple', 'pear']    # True
fruits contains only ['apple', 'banana'] # True

'apple' in fruits               # True
'pear' not in fruits            # True

List Operations on Aggregated Data

# Get all values of an information across instances
all_prices = LIST_OF_ANY(order.line_item.price)
SUM(all_prices)
SORT(all_prices)