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pegjs/lib/compiler/passes/report-left-recursion.js

66 lines
1.6 KiB
JavaScript

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