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66 lines
1.6 KiB
JavaScript
66 lines
1.6 KiB
JavaScript
var utils = require("../../utils"),
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GrammarError = require("../../grammar-error");
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/* Checks that no left recursion is present. */
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module.exports = function(ast) {
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function nop() {}
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function checkExpression(node, appliedRules) {
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check(node.expression, appliedRules);
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}
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function checkSubnodes(propertyName) {
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return function(node, appliedRules) {
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utils.each(node[propertyName], function(subnode) {
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check(subnode, appliedRules);
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});
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};
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}
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var check = utils.buildNodeVisitor({
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grammar: checkSubnodes("rules"),
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rule:
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function(node, appliedRules) {
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check(node.expression, appliedRules.concat(node.name));
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},
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named: checkExpression,
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choice: checkSubnodes("alternatives"),
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action: checkExpression,
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sequence:
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function(node, appliedRules) {
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if (node.elements.length > 0) {
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check(node.elements[0], appliedRules);
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}
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},
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labeled: checkExpression,
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text: checkExpression,
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simple_and: checkExpression,
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simple_not: checkExpression,
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semantic_and: nop,
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semantic_not: nop,
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optional: checkExpression,
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zero_or_more: checkExpression,
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one_or_more: checkExpression,
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rule_ref:
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function(node, appliedRules) {
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if (utils.contains(appliedRules, node.name)) {
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throw new GrammarError(
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"Left recursion detected for rule \"" + node.name + "\"."
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);
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}
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check(utils.findRuleByName(ast, node.name), appliedRules);
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},
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literal: nop,
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"class": nop,
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any: nop
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});
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check(ast, []);
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};
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