PEG.js grammar: Extract the |ActionExpression| rule

Having it separated from the |SequenceExpression| rule is cleaner and
more logical.

lib/parser.js

@@ -70,15 +70,10 @@ module.exports = (function() {
                 ? { type: "choice", alternatives: buildList(first, rest, 3) }
                 : first;
             },
-        peg$c11 = function(first, rest, code) {
+        peg$c11 = function(expression, code) {
-              var expression = rest.length > 0
+              return code !== null
-                ? { type: "sequence", elements: buildList(first, rest, 1) }
+                ? { type: "action", expression: expression, code: code[1] }
-                : first;
+                : expression;
-              return {
-                type:       "action",
-                expression: expression,
-                code:       code
-              };
             },
         peg$c12 = function(first, rest) {
               return rest.length > 0
@@ -748,7 +743,7 @@ module.exports = (function() {
       var s0, s1, s2, s3, s4, s5, s6, s7;
 
       s0 = peg$currPos;
-      s1 = peg$parseSequenceExpression();
+      s1 = peg$parseActionExpression();
       if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$currPos;
@@ -764,7 +759,7 @@ module.exports = (function() {
           if (s5 !== peg$FAILED) {
             s6 = peg$parse__();
             if (s6 !== peg$FAILED) {
-              s7 = peg$parseSequenceExpression();
+              s7 = peg$parseActionExpression();
               if (s7 !== peg$FAILED) {
                 s4 = [s4, s5, s6, s7];
                 s3 = s4;
@@ -799,7 +794,7 @@ module.exports = (function() {
             if (s5 !== peg$FAILED) {
               s6 = peg$parse__();
               if (s6 !== peg$FAILED) {
-                s7 = peg$parseSequenceExpression();
+                s7 = peg$parseActionExpression();
                 if (s7 !== peg$FAILED) {
                   s4 = [s4, s5, s6, s7];
                   s3 = s4;
@@ -836,6 +831,46 @@ module.exports = (function() {
       return s0;
     }
 
+    function peg$parseActionExpression() {
+      var s0, s1, s2, s3, s4;
+
+      s0 = peg$currPos;
+      s1 = peg$parseSequenceExpression();
+      if (s1 !== peg$FAILED) {
+        s2 = peg$currPos;
+        s3 = peg$parse__();
+        if (s3 !== peg$FAILED) {
+          s4 = peg$parseCodeBlock();
+          if (s4 !== peg$FAILED) {
+            s3 = [s3, s4];
+            s2 = s3;
+          } else {
+            peg$currPos = s2;
+            s2 = peg$c0;
+          }
+        } else {
+          peg$currPos = s2;
+          s2 = peg$c0;
+        }
+        if (s2 === peg$FAILED) {
+          s2 = peg$c1;
+        }
+        if (s2 !== peg$FAILED) {
+          peg$reportedPos = s0;
+          s1 = peg$c11(s1, s2);
+          s0 = s1;
+        } else {
+          peg$currPos = s0;
+          s0 = peg$c0;
+        }
+      } else {
+        peg$currPos = s0;
+        s0 = peg$c0;
+      }
+
+      return s0;
+    }
+
     function peg$parseSequenceExpression() {
       var s0, s1, s2, s3, s4, s5;
 
@@ -877,21 +912,9 @@ module.exports = (function() {
           }
         }
         if (s2 !== peg$FAILED) {
-          s3 = peg$parse__();
+          peg$reportedPos = s0;
-          if (s3 !== peg$FAILED) {
+          s1 = peg$c12(s1, s2);
-            s4 = peg$parseCodeBlock();
+          s0 = s1;
-            if (s4 !== peg$FAILED) {
-              peg$reportedPos = s0;
-              s1 = peg$c11(s1, s2, s4);
-              s0 = s1;
-            } else {
-              peg$currPos = s0;
-              s0 = peg$c0;
-            }
-          } else {
-            peg$currPos = s0;
-            s0 = peg$c0;
-          }
         } else {
           peg$currPos = s0;
           s0 = peg$c0;
@@ -900,57 +923,6 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === peg$FAILED) {
-        s0 = peg$currPos;
-        s1 = peg$parseLabeledExpression();
-        if (s1 !== peg$FAILED) {
-          s2 = [];
-          s3 = peg$currPos;
-          s4 = peg$parse__();
-          if (s4 !== peg$FAILED) {
-            s5 = peg$parseLabeledExpression();
-            if (s5 !== peg$FAILED) {
-              s4 = [s4, s5];
-              s3 = s4;
-            } else {
-              peg$currPos = s3;
-              s3 = peg$c0;
-            }
-          } else {
-            peg$currPos = s3;
-            s3 = peg$c0;
-          }
-          while (s3 !== peg$FAILED) {
-            s2.push(s3);
-            s3 = peg$currPos;
-            s4 = peg$parse__();
-            if (s4 !== peg$FAILED) {
-              s5 = peg$parseLabeledExpression();
-              if (s5 !== peg$FAILED) {
-                s4 = [s4, s5];
-                s3 = s4;
-              } else {
-                peg$currPos = s3;
-                s3 = peg$c0;
-              }
-            } else {
-              peg$currPos = s3;
-              s3 = peg$c0;
-            }
-          }
-          if (s2 !== peg$FAILED) {
-            peg$reportedPos = s0;
-            s1 = peg$c12(s1, s2);
-            s0 = s1;
-          } else {
-            peg$currPos = s0;
-            s0 = peg$c0;
-          }
-        } else {
-          peg$currPos = s0;
-          s0 = peg$c0;
-        }
-      }
 
       return s0;
     }

spec/parser.spec.js

@@ -24,6 +24,8 @@ describe("PEG.js grammar parser", function() {
         type:     "sequence",
         elements: [labeledAbcd, labeledEfgh, labeledIjkl]
       },
+      actionOnAbcd             = { type: "action", expression: literalAbcd,        code: " code " },
+      actionOnSequence         = { type: "action", expression: sequenceOfLiterals, code: " code " },
       choiceOfLiterals         = {
         type:         "choice",
         alternatives: [literalAbcd, literalEfgh, literalIjkl]
@@ -234,52 +236,41 @@ describe("PEG.js grammar parser", function() {
 
   /* Canonical ChoiceExpression is "\"abcd\" / \"efgh\" / \"ijkl\"". */
   it("parses ChoiceExpression", function() {
-    expect('start = "abcd" "efgh" "ijkl"').toParseAs(
+    expect('start = "abcd" { code }').toParseAs(
-      oneRuleGrammar(sequenceOfLiterals)
+      oneRuleGrammar(actionOnAbcd)
     );
     expect(
-      'start = "abcd" "efgh" "ijkl" / "abcd" "efgh" "ijkl" / "abcd" "efgh" "ijkl"'
+      'start = "abcd" { code } / "abcd" { code } / "abcd" { code }'
     ).toParseAs(oneRuleGrammar({
       type:         "choice",
-      alternatives: [sequenceOfLiterals, sequenceOfLiterals, sequenceOfLiterals]
+      alternatives: [actionOnAbcd, actionOnAbcd, actionOnAbcd]
     }));
     expect(
-      'start = "abcd" "efgh" "ijkl"\n/ "abcd" "efgh" "ijkl"\n/ "abcd" "efgh" "ijkl"'
+      'start = "abcd" { code }\n/ "abcd" { code }\n/ "abcd" { code }'
     ).toParseAs(oneRuleGrammar({
       type:         "choice",
-      alternatives: [sequenceOfLiterals, sequenceOfLiterals, sequenceOfLiterals]
+      alternatives: [actionOnAbcd, actionOnAbcd, actionOnAbcd]
     }));
     expect(
-      'start = "abcd" "efgh" "ijkl" /\n"abcd" "efgh" "ijkl" /\n"abcd" "efgh" "ijkl"'
+      'start = "abcd" { code } /\n"abcd" { code } /\n"abcd" { code }'
     ).toParseAs(oneRuleGrammar({
       type:         "choice",
-      alternatives: [sequenceOfLiterals, sequenceOfLiterals, sequenceOfLiterals]
+      alternatives: [actionOnAbcd, actionOnAbcd, actionOnAbcd]
     }));
   });
 
-  /* Canonical SequenceExpression is "\"abcd\" \"efgh\" \"ijkl\"". */
+  /* Canonical ActionExpression is "\"abcd\" { code }". */
-  it("parses SequenceExpression", function() {
+  it("parses ActionExpression", function() {
-    expect('start = a:"abcd" { code }').toParseAs(
+    expect('start = "abcd" "efgh" "ijkl" { code }').toParseAs(
-      oneRuleGrammar({ type: "action", expression: labeledAbcd, code: " code " })
+      oneRuleGrammar(actionOnSequence)
-    );
-    expect('start = a:"abcd"\n{ code }').toParseAs(
-      oneRuleGrammar({ type: "action", expression: labeledAbcd, code: " code " })
-    );
-    expect('start = a:"abcd" b:"efgh" c:"ijkl" { code }').toParseAs(
-      oneRuleGrammar({
-        type:       "action",
-        expression: sequenceOfLabeleds,
-        code:       " code "
-      })
     );
-    expect('start = a:"abcd"\nb:"efgh"\nc:"ijkl" { code }').toParseAs(
+    expect('start = "abcd" "efgh" "ijkl"\n{ code }').toParseAs(
-      oneRuleGrammar({
+      oneRuleGrammar(actionOnSequence)
-        type:       "action",
-        expression: sequenceOfLabeleds,
-        code:       " code "
-      })
     );
+  });
 
+  /* Canonical SequenceExpression is "\"abcd\" \"efgh\" \"ijkl\"". */
+  it("parses SequenceExpression", function() {
     expect('start = a:"abcd"').toParseAs(
       oneRuleGrammar(labeledAbcd)
     );

src/parser.pegjs

@@ -70,24 +70,21 @@ Expression
   = ChoiceExpression
 
 ChoiceExpression
-  = first:SequenceExpression rest:(__ "/" __ SequenceExpression)* {
+  = first:ActionExpression rest:(__ "/" __ ActionExpression)* {
       return rest.length > 0
         ? { type: "choice", alternatives: buildList(first, rest, 3) }
         : first;
     }
 
-SequenceExpression
+ActionExpression
-  = first:LabeledExpression rest:(__ LabeledExpression)* __ code:CodeBlock {
+  = expression:SequenceExpression code:(__ CodeBlock)? {
-      var expression = rest.length > 0
+      return code !== null
-        ? { type: "sequence", elements: buildList(first, rest, 1) }
+        ? { type: "action", expression: expression, code: code[1] }
-        : first;
+        : expression;
-      return {
-        type:       "action",
-        expression: expression,
-        code:       code
-      };
     }
-  / first:LabeledExpression rest:(__ LabeledExpression)* {
+
+SequenceExpression
+  = first:LabeledExpression rest:(__ LabeledExpression)* {
       return rest.length > 0
         ? { type: "sequence", elements: buildList(first, rest, 1) }
         : first;