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/*
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* Computes indices of variables used for storing match results and parse
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* positions in generated code. These variables are organized as one stack. The
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* following will hold after running this pass:
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*
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* * All nodes except "grammar" and "rule" nodes will have a |resultIndex|
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* property. It will contain an index of the variable that will store a
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* match result of the expression represented by the node in generated code.
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*
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* * Some nodes will have a |posIndex| property. It will contain an index of
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* the variable that will store a parse position in generated code.
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*
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* * All "rule" nodes will contain |resultIndices| property. It will contain a
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* list of values of |resultIndex| and |posIndex| properties used in rule's
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* subnodes. (This is useful to declare variables in generated code.)
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*/
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PEG.compiler.passes.computeVarIndices = function(ast) {
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function computeLeaf(node, index) { return 0; }
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function computeFromExpression(delta) {
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return function(node, index) {
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var depth;
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node.expression.resultIndex = delta.result > 0
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? index + delta.result + delta.pos
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: node.resultIndex;
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depth = compute(
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node.expression,
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index + delta.result + delta.pos
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);
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if (delta.pos !== 0) {
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node.posIndex = index + delta.pos;
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}
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return depth + delta.result + delta.pos;
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};
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}
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var compute = buildNodeVisitor({
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grammar:
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function(node, index) {
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each(node.rules, function(node) {
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node.resultIndex = index;
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compute(node, index);
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});
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},
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rule:
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function(node, index) {
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var depth;
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node.expression.resultIndex = node.resultIndex;
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depth = compute(node.expression, index);
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node.resultIndices = range(depth + 1);
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},
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named: computeFromExpression({ result: 0, pos: 0 }),
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choice:
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function(node, index) {
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var depths = map(node.alternatives, function(alternative) {
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alternative.resultIndex = node.resultIndex;
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return compute(alternative, index);
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});
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return Math.max.apply(null, depths);
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},
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action: computeFromExpression({ result: 0, pos: 1 }),
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sequence:
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function(node, index) {
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var depths = map(node.elements, function(element, i) {
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element.resultIndex = index + i + 2;
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return compute(element, index + i + 2);
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});
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node.posIndex = index + 1;
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return node.elements.length > 0
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? Math.max.apply(
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null,
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map(depths, function(d, i) { return i + d; })
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)
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+ 2
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: 1;
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},
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labeled: computeFromExpression({ result: 0, pos: 0 }),
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simple_and: computeFromExpression({ result: 0, pos: 1 }),
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simple_not: computeFromExpression({ result: 0, pos: 1 }),
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semantic_and: computeLeaf,
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semantic_not: computeLeaf,
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optional: computeFromExpression({ result: 0, pos: 0 }),
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zero_or_more: computeFromExpression({ result: 1, pos: 0 }),
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one_or_more: computeFromExpression({ result: 1, pos: 0 }),
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rule_ref: computeLeaf,
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literal: computeLeaf,
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"class": computeLeaf,
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any: computeLeaf
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});
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compute(ast, 0);
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};
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