Hooks

Hooks are functions that can be called from semantic actions and visitor callbacks. They provide contextual information and actions.

Hook	Type	Availability	Description
$from	() => Location	Semantic actions, visitors	Returns the start location of the current match in the input (included)
$to	() => Location	Semantic actions, visitors	Returns the end location of the current match in the input (excluded)
$children	() => any[]	Semantic actions	Returns the children produced by the current match
$value	() => any	Semantic actions	Returns the value (i.e. the single child) produced by the current match. This is undefined if there is no child, or multiple children.
$raw	() => string	Semantic actions, visitors	Returns the substring of the current match
$options	() => Options	Semantic actions, visitors	Returns the current parse options
$context	() => any	Semantic actions, visitors	Returns the parse context. Shortcut for $options().context.
$warn	(message: string) => void	Semantic actions, visitors	Emits a warning at the current match's start location
$fail	(message: string) => void	Semantic actions, visitors	Emits a semantic failure at the current match's start location. In semantic actions, this failure is only a candidate (see Failures and warnings).
$expected	(expected: (string | RegExp | Expectation)[]) => void	Semantic actions, visitors	Emits an expectation failure at the current match's start location. In semantic actions, this failure is only a candidate and might be thrown out or merged according to the farthest failure heuristic (see Failures and warnings).
$commit	() => void	Semantic actions	Flushes the current farthest failure to the final failure output (see Error recovery)
$emit	(children: any[]) => void	Semantic actions	Emits the given children.
$node	(label: string, fields: Record<string, any>): Node	Semantic actions, visitors	Creates a Node with the given label and fields
$visit	(node: Node, visitor?: Visitor, options?: VisitOptions) => any	Visitors	Applies the current visitor (or visitor if the second argument is provided) to node and returns the result. New options can be passed down (useful for changing context, or disabling warning and failure reports).
$parent	() => Node | null	Visitors	Returns the Node from which the current visit was called from, or null if the current node is root