Do not store result variable indices, just the counts

spec/compiler/passes/compute-var-indices.spec.js

@@ -24,8 +24,8 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a named", function() {
     expect(pass).toChangeAST('start "start" = &"a"', ruleDetails({
-      resultIndices: [0, 1],
-      expression:    {
+      resultCount: 2,
+      expression:  {
         resultIndex: 0,
         expression:  { resultIndex: 0, posIndex: 1 }
       }
@@ -34,23 +34,23 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a choice", function() {
     expect(pass).toChangeAST('start = &"a" / &"b" / &"c"', ruleDetails({
-      resultIndices: [0, 1],
-      expression:    choiceDetails
+      resultCount: 2,
+      expression:  choiceDetails
     }));
     expect(pass).toChangeAST('start = &"a" / &"b"* / &"c"', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    choiceDetails
+      resultCount: 3,
+      expression:  choiceDetails
     }));
     expect(pass).toChangeAST('start = &"a" / &(&"b") / &"c"', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    choiceDetails
+      resultCount: 3,
+      expression:  choiceDetails
     }));
   });
 
   it("computes variable indices for an action", function() {
     expect(pass).toChangeAST('start = &"a" { code }', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    {
+      resultCount: 3,
+      expression:  {
         resultIndex: 0,
         posIndex:    1,
         expression:  { resultIndex: 0, posIndex: 2 }
@@ -60,47 +60,47 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a sequence", function() {
     expect(pass).toChangeAST('start = ', ruleDetails({
-      resultIndices: [0, 1],
-      expression:    { resultIndex: 0, posIndex: 1 }
+      resultCount: 2,
+      expression:  { resultIndex: 0, posIndex: 1 }
     }));
     expect(pass).toChangeAST('start = &"a" &"b" &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5],
-      expression:    sequenceDetails
+      resultCount: 6,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &"a" &"b" &"c"*', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5, 6],
-      expression:    sequenceDetails
+      resultCount: 7,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &"a" &"b"* &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5],
-      expression:    sequenceDetails
+      resultCount: 6,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &"a" &("b"*)* &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5, 6],
-      expression:    sequenceDetails
+      resultCount: 7,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &"a"* &"b" &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5],
-      expression:    sequenceDetails
+      resultCount: 6,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &("a"*)* &"b" &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5],
-      expression:    sequenceDetails
+      resultCount: 6,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &(("a"*)*)* &"b" &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5, 6],
-      expression:    sequenceDetails
+      resultCount: 7,
+      expression:  sequenceDetails
     }));
     expect(pass).toChangeAST('start = &"a" &(&"b") &"c"', ruleDetails({
-      resultIndices: [0, 1, 2, 3, 4, 5],
-      expression:    sequenceDetails
+      resultCount: 6,
+      expression:  sequenceDetails
     }));
   });
 
   it("computes variable indices for a labeled", function() {
     expect(pass).toChangeAST('start = label:&"a"', ruleDetails({
-      resultIndices: [0, 1],
-      expression:    {
+      resultCount: 2,
+      expression:  {
         resultIndex: 0,
         expression:  { resultIndex: 0, posIndex: 1 }
       }
@@ -109,8 +109,8 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a simple and", function() {
     expect(pass).toChangeAST('start = &(&"a")', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    {
+      resultCount: 3,
+      expression:  {
         resultIndex: 0,
         posIndex:    1,
         expression:  { resultIndex: 0, posIndex: 2 }
@@ -120,8 +120,8 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a simple not", function() {
     expect(pass).toChangeAST('start = !(&"a")', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    {
+      resultCount: 3,
+      expression:  {
         resultIndex: 0,
         posIndex:    1,
         expression:  { resultIndex: 0, posIndex: 2 }
@@ -131,22 +131,22 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a semantic and", function() {
     expect(pass).toChangeAST('start = &{ code }', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 
   it("computes variable indices for a semantic not", function() {
     expect(pass).toChangeAST('start = !{ code }', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 
   it("computes variable indices for an optional", function() {
     expect(pass).toChangeAST('start = (&"a")?', ruleDetails({
-      resultIndices: [0, 1],
-      expression:    {
+      resultCount: 2,
+      expression:  {
         resultIndex: 0,
         expression:  { resultIndex: 0, posIndex: 1 }
       }
@@ -155,8 +155,8 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a zero or more", function() {
     expect(pass).toChangeAST('start = (&"a")*', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    {
+      resultCount: 3,
+      expression:  {
         resultIndex: 0,
         expression:  { resultIndex: 1, posIndex: 2 }
       }
@@ -165,8 +165,8 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a one or more", function() {
     expect(pass).toChangeAST('start = (&"a")+', ruleDetails({
-      resultIndices: [0, 1, 2],
-      expression:    {
+      resultCount: 3,
+      expression:  {
         resultIndex: 0,
         expression:  { resultIndex: 1, posIndex: 2 }
       }
@@ -175,29 +175,29 @@ describe("compiler pass |computeVarIndices|", function() {
 
   it("computes variable indices for a rule reference", function() {
     expect(pass).toChangeAST('start = a', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 
   it("computes variable indices for a literal", function() {
     expect(pass).toChangeAST('start = "a"', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 
   it("computes variable indices for a class", function() {
     expect(pass).toChangeAST('start = [a-z]', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 
   it("computes variable indices for an any", function() {
     expect(pass).toChangeAST('start = .', ruleDetails({
-      resultIndices: [0],
-      expression:    leafDetails
+      resultCount: 1,
+      expression:  leafDetails
     }));
   });
 });

src/compiler/passes/compute-var-indices.js

@@ -10,9 +10,10 @@
  *   * Some nodes will have a |posIndex| property. It will contain an index of
  *     the variable that will store a parse position in generated code.
  *
- *   * All "rule" nodes will contain |resultIndices| property. It will contain a
- *     list of values of |resultIndex| and |posIndex| properties used in rule's
- *     subnodes. (This is useful to declare variables in generated code.)
+ *   * All "rule" nodes will contain |resultCount| property. It will contain a
+ *     count of distinct values of |resultIndex| and |posIndex| properties used
+ *     in rule's subnodes. (This is useful to declare variables in generated
+ *     code.)
  */
 PEG.compiler.passes.computeVarIndices = function(ast) {
   function computeLeaf(node, index) { return 0; }
@@ -55,7 +56,7 @@ PEG.compiler.passes.computeVarIndices = function(ast) {
 
         depth = compute(node.expression, index);
 
-        node.resultIndices = range(depth + 1);
+        node.resultCount = depth + 1;
       },
 
     named:        computeFromExpression({ result: 0, pos: 0 }),

src/compiler/passes/generate-code.js

@@ -558,8 +558,8 @@ PEG.compiler.passes.generateCode = function(ast, options) {
             '    }',
             '    ',
             '  #end',
-            '  #if node.resultIndices.length > 0',
-            '    var #{map(node.resultIndices, resultVar).join(", ")};',
+            '  #if node.resultCount > 0',
+            '    var #{map(range(node.resultCount), resultVar).join(", ")};',
             '  #end',
             '  ',
             '  #block emit(node.expression)',
@@ -741,6 +741,7 @@ PEG.compiler.passes.generateCode = function(ast, options) {
 
   function fill(name, vars) {
     vars.string  = quote;
+    vars.range   = range;
     vars.map     = map;
     vars.pluck   = pluck;
     vars.keys    = keys;