PEG.js grammar: Extract the |ActionExpression| rule

Having it separated from the |SequenceExpression| rule is cleaner and more logical.
2014-04-04 10:03:22 +02:00 · 2014-04-04 10:03:22 +02:00 · 8e6f98e45c
parent 5c6f4dd38b
commit 8e6f98e45c
3 changed files with 79 additions and 119 deletions
--- a/lib/parser.js
+++ b/lib/parser.js
@ -70,15 +70,10 @@ module.exports = (function() {
                ? { type: "choice", alternatives: buildList(first, rest, 3) }
                : first;
            },
-        peg$c11 = function(first, rest, code) {
-              var expression = rest.length > 0
-                ? { type: "sequence", elements: buildList(first, rest, 1) }
-                : first;
-              return {
-                type:       "action",
-                expression: expression,
-                code:       code
-              };
+        peg$c11 = function(expression, code) {
+              return code !== null
+                ? { type: "action", expression: expression, code: code[1] }
+                : expression;
            },
        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__();
-          if (s3 !== peg$FAILED) {
-            s4 = peg$parseCodeBlock();
-            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$c0;
-          }
+          peg$reportedPos = s0;
+          s1 = peg$c12(s1, s2);
+          s0 = s1;
        } else {
          peg$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;
    }
--- a/spec/parser.spec.js
+++ b/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(
-      oneRuleGrammar(sequenceOfLiterals)
+    expect('start = "abcd" { code }').toParseAs(
+      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 ActionExpression is "\"abcd\" { code }". */
+  it("parses ActionExpression", function() {
+    expect('start = "abcd" "efgh" "ijkl" { code }').toParseAs(
+      oneRuleGrammar(actionOnSequence)
+    );
+    expect('start = "abcd" "efgh" "ijkl"\n{ code }').toParseAs(
+      oneRuleGrammar(actionOnSequence)
+    );
+  });
+
  /* Canonical SequenceExpression is "\"abcd\" \"efgh\" \"ijkl\"". */
  it("parses SequenceExpression", function() {
-    expect('start = a:"abcd" { code }').toParseAs(
-      oneRuleGrammar({ type: "action", expression: labeledAbcd, code: " code " })
-    );
-    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(
-      oneRuleGrammar({
-        type:       "action",
-        expression: sequenceOfLabeleds,
-        code:       " code "
-      })
-    );
-
    expect('start = a:"abcd"').toParseAs(
      oneRuleGrammar(labeledAbcd)
    );
--- a/src/parser.pegjs
+++ b/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
-  = first:LabeledExpression rest:(__ LabeledExpression)* __ code:CodeBlock {
-      var expression = rest.length > 0
-        ? { type: "sequence", elements: buildList(first, rest, 1) }
-        : first;
-      return {
-        type:       "action",
-        expression: expression,
-        code:       code
-      };
+ActionExpression
+  = expression:SequenceExpression code:(__ CodeBlock)? {
+      return code !== null
+        ? { type: "action", expression: expression, code: code[1] }
+        : expression;
    }
-  / first:LabeledExpression rest:(__ LabeledExpression)* {
+
+SequenceExpression
+  = first:LabeledExpression rest:(__ LabeledExpression)* {
      return rest.length > 0
        ? { type: "sequence", elements: buildList(first, rest, 1) }
        : first;