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/*
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* Computes names of variables used for storing match results and parse
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* positions in generated code. These variables are organized as two stacks.
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* The 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 |resultVar|
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* property. It will contain a name of the variable that will store a match
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* result of the expression represented by the node in generated code.
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*
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* * Some nodes will have a |posVar| property. It will contain a name of the
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* variable that will store a parse position in generated code.
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*
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* * All "rule" nodes will contain |resultVars| and |posVars| properties.
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* They will contain a list of values of |resultVar| and |posVar| properties
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* used in rule's subnodes. (This is useful to declare variables in
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* generated code.)
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*/
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PEG.compiler.passes.computeVarNames = function(ast) {
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function resultVar(index) { return "result" + index; }
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function posVar(index) { return "pos" + index; }
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function computeLeaf(node, index) {
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node.resultVar = resultVar(index.result);
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return { result: 0, pos: 0 };
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}
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function computeFromExpression(delta) {
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return function(node, index) {
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var depth = compute(
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node.expression,
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{
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result: index.result + delta.result,
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pos: index.pos + delta.pos
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}
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);
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node.resultVar = resultVar(index.result);
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if (delta.pos !== 0) {
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node.posVar = posVar(index.pos);
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}
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return {
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result: depth.result + delta.result,
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pos: depth.pos + delta.pos
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};
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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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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 = compute(node.expression, index);
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node.resultVar = resultVar(index.result);
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node.resultVars = map(range(depth.result + 1), resultVar);
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node.posVars = map(range(depth.pos), posVar);
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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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return compute(alternative, index);
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});
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node.resultVar = resultVar(index.result);
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return {
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result: Math.max.apply(null, pluck(depths, "result")),
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pos: Math.max.apply(null, pluck(depths, "pos"))
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};
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},
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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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return compute(
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element,
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{ result: index.result + i, pos: index.pos + 1 }
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);
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});
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node.resultVar = resultVar(index.result);
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node.posVar = posVar(index.pos);
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return {
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result:
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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.result; })
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)
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: 0,
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pos:
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node.elements.length > 0
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? 1 + Math.max.apply(null, pluck(depths, "pos"))
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: 1
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};
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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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action: computeFromExpression({ result: 0, pos: 1 }),
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rule_ref: computeLeaf,
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literal: computeLeaf,
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any: computeLeaf,
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"class": computeLeaf
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});
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compute(ast, { result: 0, pos: 0 });
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};
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