234 lines
8.9 KiB
JavaScript
234 lines
8.9 KiB
JavaScript
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import { isDocument, isNode, isPair, isCollection, isMap, isSeq, isScalar, isAlias } from './nodes/identity.js';
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const BREAK = Symbol('break visit');
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const SKIP = Symbol('skip children');
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const REMOVE = Symbol('remove node');
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/**
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* Apply a visitor to an AST node or document.
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*
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* Walks through the tree (depth-first) starting from `node`, calling a
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* `visitor` function with three arguments:
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* - `key`: For sequence values and map `Pair`, the node's index in the
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* collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
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* `null` for the root node.
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* - `node`: The current node.
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* - `path`: The ancestry of the current node.
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*
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* The return value of the visitor may be used to control the traversal:
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* - `undefined` (default): Do nothing and continue
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* - `visit.SKIP`: Do not visit the children of this node, continue with next
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* sibling
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* - `visit.BREAK`: Terminate traversal completely
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* - `visit.REMOVE`: Remove the current node, then continue with the next one
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* - `Node`: Replace the current node, then continue by visiting it
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* - `number`: While iterating the items of a sequence or map, set the index
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* of the next step. This is useful especially if the index of the current
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* node has changed.
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*
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* If `visitor` is a single function, it will be called with all values
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* encountered in the tree, including e.g. `null` values. Alternatively,
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* separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
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* `Alias` and `Scalar` node. To define the same visitor function for more than
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* one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
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* and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
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* specific defined one will be used for each node.
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*/
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function visit(node, visitor) {
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const visitor_ = initVisitor(visitor);
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if (isDocument(node)) {
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const cd = visit_(null, node.contents, visitor_, Object.freeze([node]));
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if (cd === REMOVE)
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node.contents = null;
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}
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else
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visit_(null, node, visitor_, Object.freeze([]));
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}
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// Without the `as symbol` casts, TS declares these in the `visit`
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// namespace using `var`, but then complains about that because
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// `unique symbol` must be `const`.
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/** Terminate visit traversal completely */
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visit.BREAK = BREAK;
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/** Do not visit the children of the current node */
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visit.SKIP = SKIP;
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/** Remove the current node */
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visit.REMOVE = REMOVE;
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function visit_(key, node, visitor, path) {
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const ctrl = callVisitor(key, node, visitor, path);
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if (isNode(ctrl) || isPair(ctrl)) {
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replaceNode(key, path, ctrl);
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return visit_(key, ctrl, visitor, path);
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}
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if (typeof ctrl !== 'symbol') {
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if (isCollection(node)) {
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path = Object.freeze(path.concat(node));
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for (let i = 0; i < node.items.length; ++i) {
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const ci = visit_(i, node.items[i], visitor, path);
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if (typeof ci === 'number')
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i = ci - 1;
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else if (ci === BREAK)
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return BREAK;
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else if (ci === REMOVE) {
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node.items.splice(i, 1);
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i -= 1;
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}
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}
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}
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else if (isPair(node)) {
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path = Object.freeze(path.concat(node));
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const ck = visit_('key', node.key, visitor, path);
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if (ck === BREAK)
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return BREAK;
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else if (ck === REMOVE)
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node.key = null;
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const cv = visit_('value', node.value, visitor, path);
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if (cv === BREAK)
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return BREAK;
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else if (cv === REMOVE)
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node.value = null;
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}
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}
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return ctrl;
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}
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/**
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* Apply an async visitor to an AST node or document.
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*
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* Walks through the tree (depth-first) starting from `node`, calling a
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* `visitor` function with three arguments:
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* - `key`: For sequence values and map `Pair`, the node's index in the
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* collection. Within a `Pair`, `'key'` or `'value'`, correspondingly.
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* `null` for the root node.
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* - `node`: The current node.
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* - `path`: The ancestry of the current node.
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*
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* The return value of the visitor may be used to control the traversal:
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* - `Promise`: Must resolve to one of the following values
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* - `undefined` (default): Do nothing and continue
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* - `visit.SKIP`: Do not visit the children of this node, continue with next
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* sibling
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* - `visit.BREAK`: Terminate traversal completely
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* - `visit.REMOVE`: Remove the current node, then continue with the next one
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* - `Node`: Replace the current node, then continue by visiting it
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* - `number`: While iterating the items of a sequence or map, set the index
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* of the next step. This is useful especially if the index of the current
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* node has changed.
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*
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* If `visitor` is a single function, it will be called with all values
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* encountered in the tree, including e.g. `null` values. Alternatively,
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* separate visitor functions may be defined for each `Map`, `Pair`, `Seq`,
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* `Alias` and `Scalar` node. To define the same visitor function for more than
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* one node type, use the `Collection` (map and seq), `Value` (map, seq & scalar)
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* and `Node` (alias, map, seq & scalar) targets. Of all these, only the most
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* specific defined one will be used for each node.
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*/
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async function visitAsync(node, visitor) {
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const visitor_ = initVisitor(visitor);
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if (isDocument(node)) {
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const cd = await visitAsync_(null, node.contents, visitor_, Object.freeze([node]));
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if (cd === REMOVE)
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node.contents = null;
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}
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else
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await visitAsync_(null, node, visitor_, Object.freeze([]));
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}
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// Without the `as symbol` casts, TS declares these in the `visit`
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// namespace using `var`, but then complains about that because
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// `unique symbol` must be `const`.
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/** Terminate visit traversal completely */
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visitAsync.BREAK = BREAK;
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/** Do not visit the children of the current node */
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visitAsync.SKIP = SKIP;
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/** Remove the current node */
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visitAsync.REMOVE = REMOVE;
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async function visitAsync_(key, node, visitor, path) {
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const ctrl = await callVisitor(key, node, visitor, path);
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if (isNode(ctrl) || isPair(ctrl)) {
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replaceNode(key, path, ctrl);
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return visitAsync_(key, ctrl, visitor, path);
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}
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if (typeof ctrl !== 'symbol') {
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if (isCollection(node)) {
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path = Object.freeze(path.concat(node));
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for (let i = 0; i < node.items.length; ++i) {
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const ci = await visitAsync_(i, node.items[i], visitor, path);
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if (typeof ci === 'number')
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i = ci - 1;
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else if (ci === BREAK)
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return BREAK;
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else if (ci === REMOVE) {
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node.items.splice(i, 1);
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i -= 1;
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}
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}
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}
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else if (isPair(node)) {
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path = Object.freeze(path.concat(node));
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const ck = await visitAsync_('key', node.key, visitor, path);
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if (ck === BREAK)
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return BREAK;
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else if (ck === REMOVE)
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node.key = null;
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const cv = await visitAsync_('value', node.value, visitor, path);
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if (cv === BREAK)
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return BREAK;
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else if (cv === REMOVE)
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node.value = null;
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}
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}
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return ctrl;
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}
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function initVisitor(visitor) {
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if (typeof visitor === 'object' &&
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(visitor.Collection || visitor.Node || visitor.Value)) {
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return Object.assign({
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Alias: visitor.Node,
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Map: visitor.Node,
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Scalar: visitor.Node,
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Seq: visitor.Node
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}, visitor.Value && {
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Map: visitor.Value,
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Scalar: visitor.Value,
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Seq: visitor.Value
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}, visitor.Collection && {
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Map: visitor.Collection,
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Seq: visitor.Collection
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}, visitor);
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}
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return visitor;
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}
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function callVisitor(key, node, visitor, path) {
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if (typeof visitor === 'function')
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return visitor(key, node, path);
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if (isMap(node))
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return visitor.Map?.(key, node, path);
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if (isSeq(node))
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return visitor.Seq?.(key, node, path);
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if (isPair(node))
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return visitor.Pair?.(key, node, path);
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if (isScalar(node))
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return visitor.Scalar?.(key, node, path);
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if (isAlias(node))
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return visitor.Alias?.(key, node, path);
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return undefined;
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}
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function replaceNode(key, path, node) {
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const parent = path[path.length - 1];
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if (isCollection(parent)) {
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parent.items[key] = node;
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}
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else if (isPair(parent)) {
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if (key === 'key')
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parent.key = node;
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else
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parent.value = node;
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}
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else if (isDocument(parent)) {
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parent.contents = node;
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}
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else {
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const pt = isAlias(parent) ? 'alias' : 'scalar';
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throw new Error(`Cannot replace node with ${pt} parent`);
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}
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}
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export { visit, visitAsync };
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