List Expressions

GQL has two expression forms that iterate over a list. They share the <variable> IN <list> shape but produce different things:

List Comprehension

A list comprehension creates a new list by iterating over an existing list, optionally filtering elements and transforming them.

Syntax
<list comprehension> ::=
  "[" <variable> "IN" <list> [ < "WHERE" | "FILTER" > <condition> ] [ "|" <expr> ] "]"

Details

• <variable>: the iteration variable, bound to each element of <list> in turn.
• WHERE|FILTER <condition>: optional filter; only elements that meet the condition are included.
• <expr>: optional transformation. if omitted, the original element is emitted.

Transform each element:

GQL
RETURN [x IN [1, 2, 3, 4, 5] | x * 10]

Result: [10, 20, 30, 40, 50]

Filter elements:

GQL
RETURN [x IN [1, 2, 3, 4, 5] WHERE x > 2]

Result: [3, 4, 5]

Filter and transform:

GQL
RETURN [x IN [1, 2, 3, 4, 5] WHERE x > 2 | x * 10]

Result: [30, 40, 50]

List Quantifiers

Quantifiers reduce a list to a single boolean by testing a condition against its elements.

Syntax
<list quantifier> ::=
  < "ANY" | "ALL" | "NONE" | "SINGLE" > "(" <variable> "IN" <list> "WHERE" <condition> ")"

GQL
RETURN ANY(x IN [1, 2, 3] WHERE x > 2),   // true
       ALL(x IN [1, 2, 3] WHERE x > 2),   // false
       NONE(x IN [1, 2, 3] WHERE x > 5),  // true
       SINGLE(x IN [1, 2, 2] WHERE x = 2) // false