From 57e806383cdcb15be3ea23ac4c0bbf5d3463e396 Mon Sep 17 00:00:00 2001
From: David Majda <david@majda.cz>
Date: Wed, 16 Oct 2013 08:08:35 +0200
Subject: [PATCH] Error handling: Use a special value (not |null|) to indicate
 failure

Using a special value to indicate match failure instead of |null| allows
actions to return |null| as a regular value. This simplifies e.g. the
JSON parser.

Note the special value is internal and intentionally undocumented. This
means that there is currently no official way how to trigger a match
failure from an action. This is a temporary state which will be fixed
soon.

The negative performance impact (see below) is probably caused by
changing lot of comparisons against |null| (which likely check the value
against a fixed constant representing |null| in the interpreter) to
comparisons against the special value (which likely check the value
against another value in the interpreter).

Implements part of #198.

Speed impact
------------
Before:     1146.82 kB/s
After:      1031.25 kB/s
Difference: -10.08%

Size impact
-----------
Before:     950817 b
After:      973269 b
Difference: 2.36%

(Measured by /tools/impact with Node.js v0.6.18 on x86_64 GNU/Linux.)
---
 README.md                                     |   2 +-
 examples/json.pegjs                           |  24 +-
 lib/compiler/passes/generate-bytecode.js      |  28 +-
 lib/compiler/passes/generate-javascript.js    |  20 +-
 lib/parser.js                                 | 734 +++++++++---------
 .../compiler/passes/generate-bytecode.spec.js |  18 +-
 spec/generated-parser.spec.js                 |  17 +-
 7 files changed, 409 insertions(+), 434 deletions(-)

diff --git a/README.md b/README.md
index aa1d36a..1549129 100644
--- a/README.md
+++ b/README.md
@@ -374,7 +374,7 @@ The action is a piece of JavaScript code that is executed as if it was inside a
 function. It gets the match results of labeled expressions in preceding
 expression as its arguments. The action should return some JavaScript value
 using the `return` statement. This value is considered match result of the
-preceding expression. The action can return `null` to indicate a match failure.
+preceding expression.
 
 The code inside the action can access all variables and functions defined in the
 initializer at the beginning of the grammar. Curly braces in the action code
diff --git a/examples/json.pegjs b/examples/json.pegjs
index 91ffa0c..43b2314 100644
--- a/examples/json.pegjs
+++ b/examples/json.pegjs
@@ -1,19 +1,5 @@
 /* JSON parser based on the grammar described at http://json.org/. */
 
-{
-  /*
-   * We can't return |null| in the |value| rule because that would mean parse
-   * failure. So we return a special object instead and convert it to |null|
-   * later.
-   */
-
-  var null_ = new Object;
-
-  function fixNull(value) {
-    return value === null_ ? null : value;
-  }
-}
-
 /* ===== Syntactical Elements ===== */
 
 start
@@ -26,9 +12,9 @@ object
 members
   = head:pair tail:("," _ pair)* {
       var result = {};
-      result[head[0]] = fixNull(head[1]);
+      result[head[0]] = head[1];
       for (var i = 0; i < tail.length; i++) {
-        result[tail[i][2][0]] = fixNull(tail[i][2][1]);
+        result[tail[i][2][0]] = tail[i][2][1];
       }
       return result;
     }
@@ -42,9 +28,9 @@ array
 
 elements
   = head:value tail:("," _ value)* {
-      var result = [fixNull(head)];
+      var result = [head];
       for (var i = 0; i < tail.length; i++) {
-        result.push(fixNull(tail[i][2]));
+        result.push(tail[i][2]);
       }
       return result;
     }
@@ -56,7 +42,7 @@ value
   / array
   / "true" _  { return true;  }
   / "false" _ { return false; }
-  / "null" _  { return null_; }
+  / "null" _  { return null;  }
 
 /* ===== Lexical Elements ===== */
 
diff --git a/lib/compiler/passes/generate-bytecode.js b/lib/compiler/passes/generate-bytecode.js
index fc9b7fc..e9d95cd 100644
--- a/lib/compiler/passes/generate-bytecode.js
+++ b/lib/compiler/passes/generate-bytecode.js
@@ -70,7 +70,7 @@ var utils = require("../../utils"),
  *
  * [11] IF_ERROR t, f
  *
- *        if (stack.top() === null) {
+ *        if (stack.top() === FAILED) {
  *          interpret(ip + 3, ip + 3 + t);
  *        } else {
  *          interpret(ip + 3 + t, ip + 3 + t + f);
@@ -78,7 +78,7 @@ var utils = require("../../utils"),
  *
  * [12] IF_NOT_ERROR t, f
  *
- *        if (stack.top() !== null) {
+ *        if (stack.top() !== FAILED) {
  *          interpret(ip + 3, ip + 3 + t);
  *        } else {
  *          interpret(ip + 3 + t, ip + 3 + t + f);
@@ -86,7 +86,7 @@ var utils = require("../../utils"),
  *
  * [13] WHILE_NOT_ERROR b
  *
- *        while(stack.top() !== null) {
+ *        while(stack.top() !== FAILED) {
  *          interpret(ip + 2, ip + 2 + b);
  *        }
  *
@@ -137,7 +137,7 @@ var utils = require("../../utils"),
  *
  * [20] FAIL e
  *
- *        stack.push(null);
+ *        stack.push(FAILED);
  *        fail(consts[e]);
  *
  * Calls
@@ -214,7 +214,7 @@ module.exports = function(ast, options) {
 
   function buildSimplePredicate(expression, negative, context) {
     var emptyStringIndex = addConst('""'),
-        nullIndex        = addConst('null');
+        failedIndex      = addConst('peg$FAILED');
 
     return buildSequence(
       [op.PUSH_CURR_POS],
@@ -235,7 +235,7 @@ module.exports = function(ast, options) {
         buildSequence(
           [op.POP],
           [negative ? op.POP_CURR_POS : op.POP],
-          [op.PUSH, nullIndex]
+          [op.PUSH, failedIndex]
         )
       )
     );
@@ -244,7 +244,7 @@ module.exports = function(ast, options) {
   function buildSemanticPredicate(code, negative, context) {
     var functionIndex    = addFunctionConst(utils.keys(context.env), code),
         emptyStringIndex = addConst('""'),
-        nullIndex        = addConst('null');
+        failedIndex      = addConst('peg$FAILED');
 
     return buildSequence(
       [op.REPORT_CURR_POS],
@@ -253,11 +253,11 @@ module.exports = function(ast, options) {
         [op.IF],
         buildSequence(
           [op.POP],
-          [op.PUSH, negative ? nullIndex : emptyStringIndex]
+          [op.PUSH, negative ? failedIndex : emptyStringIndex]
         ),
         buildSequence(
           [op.POP],
-          [op.PUSH, negative ? emptyStringIndex : nullIndex]
+          [op.PUSH, negative ? emptyStringIndex : failedIndex]
         )
       )
     );
@@ -357,7 +357,7 @@ module.exports = function(ast, options) {
     },
 
     sequence: function(node, context) {
-      var emptyArrayIndex, nullIndex;
+      var emptyArrayIndex, failIndex;
 
       function buildElementsCode(elements, context) {
         var processedCount, functionIndex;
@@ -381,7 +381,7 @@ module.exports = function(ast, options) {
               buildSequence(
                 processedCount > 1 ? [op.POP_N, processedCount] : [op.POP],
                 [op.POP_CURR_POS],
-                [op.PUSH, nullIndex]
+                [op.PUSH, failedIndex]
               )
             )
           );
@@ -409,7 +409,7 @@ module.exports = function(ast, options) {
       }
 
       if (node.elements.length > 0) {
-        nullIndex = addConst('null');
+        failedIndex = addConst('peg$FAILED');
 
         return buildSequence(
           [op.PUSH_CURR_POS],
@@ -500,7 +500,7 @@ module.exports = function(ast, options) {
 
     one_or_more: function(node, context) {
       var emptyArrayIndex = addConst('[]');
-          nullIndex       = addConst('null');
+          failedIndex     = addConst('peg$FAILED');
           expressionCode  = generate(node.expression, {
             sp:     context.sp + 1,
             env:    { },
@@ -513,7 +513,7 @@ module.exports = function(ast, options) {
         buildCondition(
           [op.IF_NOT_ERROR],
           buildSequence(buildAppendLoop(expressionCode), [op.POP]),
-          buildSequence([op.POP], [op.POP], [op.PUSH, nullIndex])
+          buildSequence([op.POP], [op.POP], [op.PUSH, failedIndex])
         )
       );
     },
diff --git a/lib/compiler/passes/generate-javascript.js b/lib/compiler/passes/generate-javascript.js
index d463f11..fadd891 100644
--- a/lib/compiler/passes/generate-javascript.js
+++ b/lib/compiler/passes/generate-javascript.js
@@ -223,18 +223,18 @@ module.exports = function(ast, options) {
       '',
       '        case ' + op.IF_ERROR + ':',         // IF_ERROR t, f
                  indent10(generateCondition(
-                   'stack[stack.length - 1] === null',
+                   'stack[stack.length - 1] === peg$FAILED',
                    0
                  )),
       '',
       '        case ' + op.IF_NOT_ERROR + ':',     // IF_NOT_ERROR t, f
                  indent10(
-                   generateCondition('stack[stack.length - 1] !== null',
+                   generateCondition('stack[stack.length - 1] !== peg$FAILED',
                    0
                  )),
       '',
       '        case ' + op.WHILE_NOT_ERROR + ':',  // WHILE_NOT_ERROR b
-                 indent10(generateLoop('stack[stack.length - 1] !== null')),
+                 indent10(generateLoop('stack[stack.length - 1] !== peg$FAILED')),
       '',
       '        case ' + op.MATCH_ANY + ':',        // MATCH_ANY a, f, ...
                  indent10(generateCondition('input.length > peg$currPos', 0)),
@@ -270,7 +270,7 @@ module.exports = function(ast, options) {
       '          break;',
       '',
       '        case ' + op.FAIL + ':',             // FAIL e
-      '          stack.push(null);',
+      '          stack.push(peg$FAILED);',
       '          if (peg$silentFails === 0) {',
       '            peg$fail(peg$consts[bc[ip + 1]]);',
       '          }',
@@ -515,15 +515,15 @@ module.exports = function(ast, options) {
             break;
 
           case op.IF_ERROR:         // IF_ERROR t, f
-            compileCondition(stack.top() + ' === null', 0);
+            compileCondition(stack.top() + ' === peg$FAILED', 0);
             break;
 
           case op.IF_NOT_ERROR:     // IF_NOT_ERROR t, f
-            compileCondition(stack.top() + ' !== null', 0);
+            compileCondition(stack.top() + ' !== peg$FAILED', 0);
             break;
 
           case op.WHILE_NOT_ERROR:  // WHILE_NOT_ERROR b
-            compileLoop(stack.top() + ' !== null', 0);
+            compileLoop(stack.top() + ' !== peg$FAILED', 0);
             break;
 
           case op.MATCH_ANY:        // MATCH_ANY a, f, ...
@@ -585,7 +585,7 @@ module.exports = function(ast, options) {
             break;
 
           case op.FAIL:             // FAIL e
-            parts.push(stack.push('null'));
+            parts.push(stack.push('peg$FAILED'));
             parts.push('if (peg$silentFails === 0) { peg$fail(' + c(bc[ip + 1]) + '); }');
             ip += 2;
             break;
@@ -745,6 +745,8 @@ module.exports = function(ast, options) {
     '',
     '  function parse(input) {',
     '    var options = arguments.length > 1 ? arguments[1] : {},',
+    '',
+    '        peg$FAILED = {},',
     ''
   ].join('\n'));
 
@@ -937,7 +939,7 @@ module.exports = function(ast, options) {
 
   parts.push([
     '',
-    '    if (peg$result !== null && peg$currPos === input.length) {',
+    '    if (peg$result !== peg$FAILED && peg$currPos === input.length) {',
     '      return peg$result;',
     '    } else {',
     '      peg$cleanupExpected(peg$maxFailExpected);',
diff --git a/lib/parser.js b/lib/parser.js
index ab6b1cf..ded3551 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -73,10 +73,12 @@ module.exports = (function() {
   function parse(input) {
     var options = arguments.length > 1 ? arguments[1] : {},
 
+        peg$FAILED = {},
+
         peg$startRuleFunctions = { grammar: peg$parsegrammar },
         peg$startRuleFunction  = peg$parsegrammar,
 
-        peg$c0 = null,
+        peg$c0 = peg$FAILED,
         peg$c1 = "",
         peg$c2 = [],
         peg$c3 = function(initializer, rules) {
@@ -482,26 +484,26 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parse__();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parseinitializer();
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$c1;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = [];
           s4 = peg$parserule();
-          if (s4 !== null) {
-            while (s4 !== null) {
+          if (s4 !== peg$FAILED) {
+            while (s4 !== peg$FAILED) {
               s3.push(s4);
               s4 = peg$parserule();
             }
           } else {
             s3 = peg$c0;
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c3(s2, s3);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -528,15 +530,15 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseaction();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parsesemicolon();
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$c1;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c4(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -559,24 +561,24 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseidentifier();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parsestring();
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$c1;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = peg$parseequals();
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             s4 = peg$parsechoice();
-            if (s4 !== null) {
+            if (s4 !== peg$FAILED) {
               s5 = peg$parsesemicolon();
-              if (s5 === null) {
+              if (s5 === peg$FAILED) {
                 s5 = peg$c1;
               }
-              if (s5 !== null) {
+              if (s5 !== peg$FAILED) {
                 peg$reportedPos = s0;
                 s1 = peg$c5(s1, s2, s4);
-                if (s1 === null) {
+                if (s1 === peg$FAILED) {
                   peg$currPos = s0;
                   s0 = s1;
                 } else {
@@ -611,13 +613,13 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parsesequence();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$currPos;
         s4 = peg$parseslash();
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           s5 = peg$parsesequence();
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s4 = [s4, s5];
             s3 = s4;
           } else {
@@ -628,13 +630,13 @@ module.exports = (function() {
           peg$currPos = s3;
           s3 = peg$c0;
         }
-        while (s3 !== null) {
+        while (s3 !== peg$FAILED) {
           s2.push(s3);
           s3 = peg$currPos;
           s4 = peg$parseslash();
-          if (s4 !== null) {
+          if (s4 !== peg$FAILED) {
             s5 = peg$parsesequence();
-            if (s5 !== null) {
+            if (s5 !== peg$FAILED) {
               s4 = [s4, s5];
               s3 = s4;
             } else {
@@ -646,10 +648,10 @@ module.exports = (function() {
             s3 = peg$c0;
           }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c6(s1, s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -673,16 +675,16 @@ module.exports = (function() {
       s0 = peg$currPos;
       s1 = [];
       s2 = peg$parselabeled();
-      while (s2 !== null) {
+      while (s2 !== peg$FAILED) {
         s1.push(s2);
         s2 = peg$parselabeled();
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parseaction();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c7(s1, s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -696,19 +698,19 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$currPos;
         s1 = [];
         s2 = peg$parselabeled();
-        while (s2 !== null) {
+        while (s2 !== peg$FAILED) {
           s1.push(s2);
           s2 = peg$parselabeled();
         }
-        if (s1 !== null) {
+        if (s1 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c8(s1);
         }
-        if (s1 === null) {
+        if (s1 === peg$FAILED) {
           peg$currPos = s0;
           s0 = s1;
         } else {
@@ -724,14 +726,14 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseidentifier();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parsecolon();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = peg$parseprefixed();
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c9(s1, s3);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -749,7 +751,7 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parseprefixed();
       }
 
@@ -761,12 +763,12 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parsedollar();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parsesuffixed();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c10(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -780,15 +782,15 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$currPos;
         s1 = peg$parseand();
-        if (s1 !== null) {
+        if (s1 !== peg$FAILED) {
           s2 = peg$parseaction();
-          if (s2 !== null) {
+          if (s2 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c11(s2);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -802,15 +804,15 @@ module.exports = (function() {
           peg$currPos = s0;
           s0 = peg$c0;
         }
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$currPos;
           s1 = peg$parseand();
-          if (s1 !== null) {
+          if (s1 !== peg$FAILED) {
             s2 = peg$parsesuffixed();
-            if (s2 !== null) {
+            if (s2 !== peg$FAILED) {
               peg$reportedPos = s0;
               s1 = peg$c12(s2);
-              if (s1 === null) {
+              if (s1 === peg$FAILED) {
                 peg$currPos = s0;
                 s0 = s1;
               } else {
@@ -824,15 +826,15 @@ module.exports = (function() {
             peg$currPos = s0;
             s0 = peg$c0;
           }
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$currPos;
             s1 = peg$parsenot();
-            if (s1 !== null) {
+            if (s1 !== peg$FAILED) {
               s2 = peg$parseaction();
-              if (s2 !== null) {
+              if (s2 !== peg$FAILED) {
                 peg$reportedPos = s0;
                 s1 = peg$c13(s2);
-                if (s1 === null) {
+                if (s1 === peg$FAILED) {
                   peg$currPos = s0;
                   s0 = s1;
                 } else {
@@ -846,15 +848,15 @@ module.exports = (function() {
               peg$currPos = s0;
               s0 = peg$c0;
             }
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               s0 = peg$currPos;
               s1 = peg$parsenot();
-              if (s1 !== null) {
+              if (s1 !== peg$FAILED) {
                 s2 = peg$parsesuffixed();
-                if (s2 !== null) {
+                if (s2 !== peg$FAILED) {
                   peg$reportedPos = s0;
                   s1 = peg$c14(s2);
-                  if (s1 === null) {
+                  if (s1 === peg$FAILED) {
                     peg$currPos = s0;
                     s0 = s1;
                   } else {
@@ -868,7 +870,7 @@ module.exports = (function() {
                 peg$currPos = s0;
                 s0 = peg$c0;
               }
-              if (s0 === null) {
+              if (s0 === peg$FAILED) {
                 s0 = peg$parsesuffixed();
               }
             }
@@ -884,12 +886,12 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseprimary();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parsequestion();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c15(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -903,15 +905,15 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$currPos;
         s1 = peg$parseprimary();
-        if (s1 !== null) {
+        if (s1 !== peg$FAILED) {
           s2 = peg$parsestar();
-          if (s2 !== null) {
+          if (s2 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c16(s1);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -925,15 +927,15 @@ module.exports = (function() {
           peg$currPos = s0;
           s0 = peg$c0;
         }
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$currPos;
           s1 = peg$parseprimary();
-          if (s1 !== null) {
+          if (s1 !== peg$FAILED) {
             s2 = peg$parseplus();
-            if (s2 !== null) {
+            if (s2 !== peg$FAILED) {
               peg$reportedPos = s0;
               s1 = peg$c17(s1);
-              if (s1 === null) {
+              if (s1 === peg$FAILED) {
                 peg$currPos = s0;
                 s0 = s1;
               } else {
@@ -947,7 +949,7 @@ module.exports = (function() {
             peg$currPos = s0;
             s0 = peg$c0;
           }
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$parseprimary();
           }
         }
@@ -961,17 +963,17 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseidentifier();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$currPos;
         peg$silentFails++;
         s3 = peg$currPos;
         s4 = peg$parsestring();
-        if (s4 === null) {
+        if (s4 === peg$FAILED) {
           s4 = peg$c1;
         }
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           s5 = peg$parseequals();
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s4 = [s4, s5];
             s3 = s4;
           } else {
@@ -983,16 +985,16 @@ module.exports = (function() {
           s3 = peg$c0;
         }
         peg$silentFails--;
-        if (s3 === null) {
+        if (s3 === peg$FAILED) {
           s2 = peg$c1;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c18(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1006,34 +1008,34 @@ module.exports = (function() {
         peg$currPos = s0;
         s0 = peg$c0;
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parseliteral();
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$parseclass();
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$currPos;
             s1 = peg$parsedot();
-            if (s1 !== null) {
+            if (s1 !== peg$FAILED) {
               peg$reportedPos = s0;
               s1 = peg$c19();
             }
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
               s0 = s1;
             }
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               s0 = peg$currPos;
               s1 = peg$parselparen();
-              if (s1 !== null) {
+              if (s1 !== peg$FAILED) {
                 s2 = peg$parsechoice();
-                if (s2 !== null) {
+                if (s2 !== peg$FAILED) {
                   s3 = peg$parserparen();
-                  if (s3 !== null) {
+                  if (s3 !== peg$FAILED) {
                     peg$reportedPos = s0;
                     s1 = peg$c20(s2);
-                    if (s1 === null) {
+                    if (s1 === peg$FAILED) {
                       peg$currPos = s0;
                       s0 = s1;
                     } else {
@@ -1065,12 +1067,12 @@ module.exports = (function() {
       peg$silentFails++;
       s0 = peg$currPos;
       s1 = peg$parsebraced();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c22(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1085,8 +1087,8 @@ module.exports = (function() {
         s0 = peg$c0;
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c21); }
       }
 
@@ -1102,31 +1104,31 @@ module.exports = (function() {
         s2 = peg$c23;
         peg$currPos++;
       } else {
-        s2 = null;
+        s2 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c24); }
       }
-      if (s2 !== null) {
+      if (s2 !== peg$FAILED) {
         s3 = [];
         s4 = peg$parsebraced();
-        if (s4 === null) {
+        if (s4 === peg$FAILED) {
           s4 = peg$parsenonBraceCharacters();
         }
-        while (s4 !== null) {
+        while (s4 !== peg$FAILED) {
           s3.push(s4);
           s4 = peg$parsebraced();
-          if (s4 === null) {
+          if (s4 === peg$FAILED) {
             s4 = peg$parsenonBraceCharacters();
           }
         }
-        if (s3 !== null) {
+        if (s3 !== peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 125) {
             s4 = peg$c25;
             peg$currPos++;
           } else {
-            s4 = null;
+            s4 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c26); }
           }
-          if (s4 !== null) {
+          if (s4 !== peg$FAILED) {
             s2 = [s2, s3, s4];
             s1 = s2;
           } else {
@@ -1141,7 +1143,7 @@ module.exports = (function() {
         peg$currPos = s1;
         s1 = peg$c0;
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s1 = input.substring(s0, peg$currPos);
       }
       s0 = s1;
@@ -1154,8 +1156,8 @@ module.exports = (function() {
 
       s0 = [];
       s1 = peg$parsenonBraceCharacter();
-      if (s1 !== null) {
-        while (s1 !== null) {
+      if (s1 !== peg$FAILED) {
+        while (s1 !== peg$FAILED) {
           s0.push(s1);
           s1 = peg$parsenonBraceCharacter();
         }
@@ -1173,7 +1175,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c28); }
       }
 
@@ -1188,15 +1190,15 @@ module.exports = (function() {
         s1 = peg$c29;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c30); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c31();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1222,15 +1224,15 @@ module.exports = (function() {
         s1 = peg$c32;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c33); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c34();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1256,15 +1258,15 @@ module.exports = (function() {
         s1 = peg$c35;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c36); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c37();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1290,15 +1292,15 @@ module.exports = (function() {
         s1 = peg$c38;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c39); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c40();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1324,15 +1326,15 @@ module.exports = (function() {
         s1 = peg$c41;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c42); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c43();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1358,15 +1360,15 @@ module.exports = (function() {
         s1 = peg$c44;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c45); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c46();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1392,15 +1394,15 @@ module.exports = (function() {
         s1 = peg$c47;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c48); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c49();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1426,15 +1428,15 @@ module.exports = (function() {
         s1 = peg$c50;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c51); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c52();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1460,15 +1462,15 @@ module.exports = (function() {
         s1 = peg$c53;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c54); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c55();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1494,15 +1496,15 @@ module.exports = (function() {
         s1 = peg$c56;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c57); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c58();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1528,15 +1530,15 @@ module.exports = (function() {
         s1 = peg$c59;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c60); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c61();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1562,15 +1564,15 @@ module.exports = (function() {
         s1 = peg$c62;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c63); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c64();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1596,15 +1598,15 @@ module.exports = (function() {
         s1 = peg$c65;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c66); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c67();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1630,47 +1632,47 @@ module.exports = (function() {
       s1 = peg$currPos;
       s2 = peg$currPos;
       s3 = peg$parseletter();
-      if (s3 === null) {
+      if (s3 === peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 95) {
           s3 = peg$c69;
           peg$currPos++;
         } else {
-          s3 = null;
+          s3 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c70); }
         }
       }
-      if (s3 !== null) {
+      if (s3 !== peg$FAILED) {
         s4 = [];
         s5 = peg$parseletter();
-        if (s5 === null) {
+        if (s5 === peg$FAILED) {
           s5 = peg$parsedigit();
-          if (s5 === null) {
+          if (s5 === peg$FAILED) {
             if (input.charCodeAt(peg$currPos) === 95) {
               s5 = peg$c69;
               peg$currPos++;
             } else {
-              s5 = null;
+              s5 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c70); }
             }
           }
         }
-        while (s5 !== null) {
+        while (s5 !== peg$FAILED) {
           s4.push(s5);
           s5 = peg$parseletter();
-          if (s5 === null) {
+          if (s5 === peg$FAILED) {
             s5 = peg$parsedigit();
-            if (s5 === null) {
+            if (s5 === peg$FAILED) {
               if (input.charCodeAt(peg$currPos) === 95) {
                 s5 = peg$c69;
                 peg$currPos++;
               } else {
-                s5 = null;
+                s5 = peg$FAILED;
                 if (peg$silentFails === 0) { peg$fail(peg$c70); }
               }
             }
           }
         }
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           s3 = [s3, s4];
           s2 = s3;
         } else {
@@ -1681,16 +1683,16 @@ module.exports = (function() {
         peg$currPos = s2;
         s2 = peg$c0;
       }
-      if (s2 !== null) {
+      if (s2 !== peg$FAILED) {
         s2 = input.substring(s1, peg$currPos);
       }
       s1 = s2;
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c71(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1705,8 +1707,8 @@ module.exports = (function() {
         s0 = peg$c0;
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c68); }
       }
 
@@ -1719,26 +1721,26 @@ module.exports = (function() {
       peg$silentFails++;
       s0 = peg$currPos;
       s1 = peg$parsedoubleQuotedString();
-      if (s1 === null) {
+      if (s1 === peg$FAILED) {
         s1 = peg$parsesingleQuotedString();
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 105) {
           s2 = peg$c73;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c74); }
         }
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$c1;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = peg$parse__();
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c75(s1, s2);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -1757,8 +1759,8 @@ module.exports = (function() {
         s0 = peg$c0;
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c72); }
       }
 
@@ -1771,15 +1773,15 @@ module.exports = (function() {
       peg$silentFails++;
       s0 = peg$currPos;
       s1 = peg$parsedoubleQuotedString();
-      if (s1 === null) {
+      if (s1 === peg$FAILED) {
         s1 = peg$parsesingleQuotedString();
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parse__();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c77(s1);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1794,8 +1796,8 @@ module.exports = (function() {
         s0 = peg$c0;
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c76); }
       }
 
@@ -1810,28 +1812,28 @@ module.exports = (function() {
         s1 = peg$c78;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c79); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$parsedoubleQuotedCharacter();
-        while (s3 !== null) {
+        while (s3 !== peg$FAILED) {
           s2.push(s3);
           s3 = peg$parsedoubleQuotedCharacter();
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 34) {
             s3 = peg$c78;
             peg$currPos++;
           } else {
-            s3 = null;
+            s3 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c79); }
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c80(s2);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -1857,15 +1859,15 @@ module.exports = (function() {
       var s0;
 
       s0 = peg$parsesimpleDoubleQuotedCharacter();
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parsesimpleEscapeSequence();
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$parsezeroEscapeSequence();
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$parsehexEscapeSequence();
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               s0 = peg$parseunicodeEscapeSequence();
-              if (s0 === null) {
+              if (s0 === peg$FAILED) {
                 s0 = peg$parseeolEscapeSequence();
               }
             }
@@ -1886,40 +1888,40 @@ module.exports = (function() {
         s2 = peg$c78;
         peg$currPos++;
       } else {
-        s2 = null;
+        s2 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c79); }
       }
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 92) {
           s2 = peg$c81;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c82); }
         }
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$parseeolChar();
         }
       }
       peg$silentFails--;
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         s1 = peg$c1;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.length > peg$currPos) {
           s2 = input.charAt(peg$currPos);
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c83); }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c84(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -1945,28 +1947,28 @@ module.exports = (function() {
         s1 = peg$c85;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c86); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$parsesingleQuotedCharacter();
-        while (s3 !== null) {
+        while (s3 !== peg$FAILED) {
           s2.push(s3);
           s3 = peg$parsesingleQuotedCharacter();
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 39) {
             s3 = peg$c85;
             peg$currPos++;
           } else {
-            s3 = null;
+            s3 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c86); }
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c80(s2);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -1992,15 +1994,15 @@ module.exports = (function() {
       var s0;
 
       s0 = peg$parsesimpleSingleQuotedCharacter();
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parsesimpleEscapeSequence();
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$parsezeroEscapeSequence();
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$parsehexEscapeSequence();
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               s0 = peg$parseunicodeEscapeSequence();
-              if (s0 === null) {
+              if (s0 === peg$FAILED) {
                 s0 = peg$parseeolEscapeSequence();
               }
             }
@@ -2021,40 +2023,40 @@ module.exports = (function() {
         s2 = peg$c85;
         peg$currPos++;
       } else {
-        s2 = null;
+        s2 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c86); }
       }
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 92) {
           s2 = peg$c81;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c82); }
         }
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$parseeolChar();
         }
       }
       peg$silentFails--;
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         s1 = peg$c1;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.length > peg$currPos) {
           s2 = input.charAt(peg$currPos);
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c83); }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c84(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2081,58 +2083,58 @@ module.exports = (function() {
         s1 = peg$c88;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c89); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 94) {
           s2 = peg$c90;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c91); }
         }
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$c1;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = [];
           s4 = peg$parseclassCharacterRange();
-          if (s4 === null) {
+          if (s4 === peg$FAILED) {
             s4 = peg$parseclassCharacter();
           }
-          while (s4 !== null) {
+          while (s4 !== peg$FAILED) {
             s3.push(s4);
             s4 = peg$parseclassCharacterRange();
-            if (s4 === null) {
+            if (s4 === peg$FAILED) {
               s4 = peg$parseclassCharacter();
             }
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             if (input.charCodeAt(peg$currPos) === 93) {
               s4 = peg$c92;
               peg$currPos++;
             } else {
-              s4 = null;
+              s4 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c93); }
             }
-            if (s4 !== null) {
+            if (s4 !== peg$FAILED) {
               if (input.charCodeAt(peg$currPos) === 105) {
                 s5 = peg$c73;
                 peg$currPos++;
               } else {
-                s5 = null;
+                s5 = peg$FAILED;
                 if (peg$silentFails === 0) { peg$fail(peg$c74); }
               }
-              if (s5 === null) {
+              if (s5 === peg$FAILED) {
                 s5 = peg$c1;
               }
-              if (s5 !== null) {
+              if (s5 !== peg$FAILED) {
                 s6 = peg$parse__();
-                if (s6 !== null) {
+                if (s6 !== peg$FAILED) {
                   peg$reportedPos = s0;
                   s1 = peg$c94(s2, s3, s5);
-                  if (s1 === null) {
+                  if (s1 === peg$FAILED) {
                     peg$currPos = s0;
                     s0 = s1;
                   } else {
@@ -2163,8 +2165,8 @@ module.exports = (function() {
         s0 = peg$c0;
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c87); }
       }
 
@@ -2176,20 +2178,20 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parseclassCharacter();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 45) {
           s2 = peg$c95;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c96); }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s3 = peg$parseclassCharacter();
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c97(s1, s3);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -2216,11 +2218,11 @@ module.exports = (function() {
 
       s0 = peg$currPos;
       s1 = peg$parsebracketDelimitedCharacter();
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         peg$reportedPos = s0;
         s1 = peg$c98(s1);
       }
-      if (s1 === null) {
+      if (s1 === peg$FAILED) {
         peg$currPos = s0;
         s0 = s1;
       } else {
@@ -2234,15 +2236,15 @@ module.exports = (function() {
       var s0;
 
       s0 = peg$parsesimpleBracketDelimitedCharacter();
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parsesimpleEscapeSequence();
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           s0 = peg$parsezeroEscapeSequence();
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             s0 = peg$parsehexEscapeSequence();
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               s0 = peg$parseunicodeEscapeSequence();
-              if (s0 === null) {
+              if (s0 === peg$FAILED) {
                 s0 = peg$parseeolEscapeSequence();
               }
             }
@@ -2263,40 +2265,40 @@ module.exports = (function() {
         s2 = peg$c92;
         peg$currPos++;
       } else {
-        s2 = null;
+        s2 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c93); }
       }
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         if (input.charCodeAt(peg$currPos) === 92) {
           s2 = peg$c81;
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c82); }
         }
-        if (s2 === null) {
+        if (s2 === peg$FAILED) {
           s2 = peg$parseeolChar();
         }
       }
       peg$silentFails--;
-      if (s2 === null) {
+      if (s2 === peg$FAILED) {
         s1 = peg$c1;
       } else {
         peg$currPos = s1;
         s1 = peg$c0;
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         if (input.length > peg$currPos) {
           s2 = input.charAt(peg$currPos);
           peg$currPos++;
         } else {
-          s2 = null;
+          s2 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c83); }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c84(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2322,53 +2324,53 @@ module.exports = (function() {
         s1 = peg$c81;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c82); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$currPos;
         peg$silentFails++;
         s3 = peg$parsedigit();
-        if (s3 === null) {
+        if (s3 === peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 120) {
             s3 = peg$c99;
             peg$currPos++;
           } else {
-            s3 = null;
+            s3 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c100); }
           }
-          if (s3 === null) {
+          if (s3 === peg$FAILED) {
             if (input.charCodeAt(peg$currPos) === 117) {
               s3 = peg$c101;
               peg$currPos++;
             } else {
-              s3 = null;
+              s3 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c102); }
             }
-            if (s3 === null) {
+            if (s3 === peg$FAILED) {
               s3 = peg$parseeolChar();
             }
           }
         }
         peg$silentFails--;
-        if (s3 === null) {
+        if (s3 === peg$FAILED) {
           s2 = peg$c1;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           if (input.length > peg$currPos) {
             s3 = input.charAt(peg$currPos);
             peg$currPos++;
           } else {
-            s3 = null;
+            s3 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c83); }
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             peg$reportedPos = s0;
             s1 = peg$c103(s3);
-            if (s1 === null) {
+            if (s1 === peg$FAILED) {
               peg$currPos = s0;
               s0 = s1;
             } else {
@@ -2398,24 +2400,24 @@ module.exports = (function() {
         s1 = peg$c104;
         peg$currPos += 2;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c105); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$currPos;
         peg$silentFails++;
         s3 = peg$parsedigit();
         peg$silentFails--;
-        if (s3 === null) {
+        if (s3 === peg$FAILED) {
           s2 = peg$c1;
         } else {
           peg$currPos = s2;
           s2 = peg$c0;
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c106();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2441,16 +2443,16 @@ module.exports = (function() {
         s1 = peg$c107;
         peg$currPos += 2;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c108); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$currPos;
         s3 = peg$currPos;
         s4 = peg$parsehexDigit();
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           s5 = peg$parsehexDigit();
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s4 = [s4, s5];
             s3 = s4;
           } else {
@@ -2461,14 +2463,14 @@ module.exports = (function() {
           peg$currPos = s3;
           s3 = peg$c0;
         }
-        if (s3 !== null) {
+        if (s3 !== peg$FAILED) {
           s3 = input.substring(s2, peg$currPos);
         }
         s2 = s3;
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c109(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2494,20 +2496,20 @@ module.exports = (function() {
         s1 = peg$c110;
         peg$currPos += 2;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c111); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$currPos;
         s3 = peg$currPos;
         s4 = peg$parsehexDigit();
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           s5 = peg$parsehexDigit();
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s6 = peg$parsehexDigit();
-            if (s6 !== null) {
+            if (s6 !== peg$FAILED) {
               s7 = peg$parsehexDigit();
-              if (s7 !== null) {
+              if (s7 !== peg$FAILED) {
                 s4 = [s4, s5, s6, s7];
                 s3 = s4;
               } else {
@@ -2526,14 +2528,14 @@ module.exports = (function() {
           peg$currPos = s3;
           s3 = peg$c0;
         }
-        if (s3 !== null) {
+        if (s3 !== peg$FAILED) {
           s3 = input.substring(s2, peg$currPos);
         }
         s2 = s3;
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c109(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2559,15 +2561,15 @@ module.exports = (function() {
         s1 = peg$c81;
         peg$currPos++;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c82); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = peg$parseeol();
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           peg$reportedPos = s0;
           s1 = peg$c112(s2);
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             peg$currPos = s0;
             s0 = s1;
           } else {
@@ -2592,7 +2594,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c114); }
       }
 
@@ -2606,7 +2608,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c116); }
       }
 
@@ -2617,7 +2619,7 @@ module.exports = (function() {
       var s0;
 
       s0 = peg$parselowerCaseLetter();
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parseupperCaseLetter();
       }
 
@@ -2631,7 +2633,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c118); }
       }
 
@@ -2645,7 +2647,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c120); }
       }
 
@@ -2657,18 +2659,18 @@ module.exports = (function() {
 
       s0 = [];
       s1 = peg$parsewhitespace();
-      if (s1 === null) {
+      if (s1 === peg$FAILED) {
         s1 = peg$parseeol();
-        if (s1 === null) {
+        if (s1 === peg$FAILED) {
           s1 = peg$parsecomment();
         }
       }
-      while (s1 !== null) {
+      while (s1 !== peg$FAILED) {
         s0.push(s1);
         s1 = peg$parsewhitespace();
-        if (s1 === null) {
+        if (s1 === peg$FAILED) {
           s1 = peg$parseeol();
-          if (s1 === null) {
+          if (s1 === peg$FAILED) {
             s1 = peg$parsecomment();
           }
         }
@@ -2682,12 +2684,12 @@ module.exports = (function() {
 
       peg$silentFails++;
       s0 = peg$parsesingleLineComment();
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         s0 = peg$parsemultiLineComment();
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c121); }
       }
 
@@ -2702,31 +2704,31 @@ module.exports = (function() {
         s1 = peg$c122;
         peg$currPos += 2;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c123); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$currPos;
         s4 = peg$currPos;
         peg$silentFails++;
         s5 = peg$parseeolChar();
         peg$silentFails--;
-        if (s5 === null) {
+        if (s5 === peg$FAILED) {
           s4 = peg$c1;
         } else {
           peg$currPos = s4;
           s4 = peg$c0;
         }
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           if (input.length > peg$currPos) {
             s5 = input.charAt(peg$currPos);
             peg$currPos++;
           } else {
-            s5 = null;
+            s5 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c83); }
           }
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s4 = [s4, s5];
             s3 = s4;
           } else {
@@ -2737,28 +2739,28 @@ module.exports = (function() {
           peg$currPos = s3;
           s3 = peg$c0;
         }
-        while (s3 !== null) {
+        while (s3 !== peg$FAILED) {
           s2.push(s3);
           s3 = peg$currPos;
           s4 = peg$currPos;
           peg$silentFails++;
           s5 = peg$parseeolChar();
           peg$silentFails--;
-          if (s5 === null) {
+          if (s5 === peg$FAILED) {
             s4 = peg$c1;
           } else {
             peg$currPos = s4;
             s4 = peg$c0;
           }
-          if (s4 !== null) {
+          if (s4 !== peg$FAILED) {
             if (input.length > peg$currPos) {
               s5 = input.charAt(peg$currPos);
               peg$currPos++;
             } else {
-              s5 = null;
+              s5 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c83); }
             }
-            if (s5 !== null) {
+            if (s5 !== peg$FAILED) {
               s4 = [s4, s5];
               s3 = s4;
             } else {
@@ -2770,7 +2772,7 @@ module.exports = (function() {
             s3 = peg$c0;
           }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           s1 = [s1, s2];
           s0 = s1;
         } else {
@@ -2793,10 +2795,10 @@ module.exports = (function() {
         s1 = peg$c124;
         peg$currPos += 2;
       } else {
-        s1 = null;
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c125); }
       }
-      if (s1 !== null) {
+      if (s1 !== peg$FAILED) {
         s2 = [];
         s3 = peg$currPos;
         s4 = peg$currPos;
@@ -2805,25 +2807,25 @@ module.exports = (function() {
           s5 = peg$c126;
           peg$currPos += 2;
         } else {
-          s5 = null;
+          s5 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c127); }
         }
         peg$silentFails--;
-        if (s5 === null) {
+        if (s5 === peg$FAILED) {
           s4 = peg$c1;
         } else {
           peg$currPos = s4;
           s4 = peg$c0;
         }
-        if (s4 !== null) {
+        if (s4 !== peg$FAILED) {
           if (input.length > peg$currPos) {
             s5 = input.charAt(peg$currPos);
             peg$currPos++;
           } else {
-            s5 = null;
+            s5 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c83); }
           }
-          if (s5 !== null) {
+          if (s5 !== peg$FAILED) {
             s4 = [s4, s5];
             s3 = s4;
           } else {
@@ -2834,7 +2836,7 @@ module.exports = (function() {
           peg$currPos = s3;
           s3 = peg$c0;
         }
-        while (s3 !== null) {
+        while (s3 !== peg$FAILED) {
           s2.push(s3);
           s3 = peg$currPos;
           s4 = peg$currPos;
@@ -2843,25 +2845,25 @@ module.exports = (function() {
             s5 = peg$c126;
             peg$currPos += 2;
           } else {
-            s5 = null;
+            s5 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c127); }
           }
           peg$silentFails--;
-          if (s5 === null) {
+          if (s5 === peg$FAILED) {
             s4 = peg$c1;
           } else {
             peg$currPos = s4;
             s4 = peg$c0;
           }
-          if (s4 !== null) {
+          if (s4 !== peg$FAILED) {
             if (input.length > peg$currPos) {
               s5 = input.charAt(peg$currPos);
               peg$currPos++;
             } else {
-              s5 = null;
+              s5 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c83); }
             }
-            if (s5 !== null) {
+            if (s5 !== peg$FAILED) {
               s4 = [s4, s5];
               s3 = s4;
             } else {
@@ -2873,15 +2875,15 @@ module.exports = (function() {
             s3 = peg$c0;
           }
         }
-        if (s2 !== null) {
+        if (s2 !== peg$FAILED) {
           if (input.substr(peg$currPos, 2) === peg$c126) {
             s3 = peg$c126;
             peg$currPos += 2;
           } else {
-            s3 = null;
+            s3 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c127); }
           }
-          if (s3 !== null) {
+          if (s3 !== peg$FAILED) {
             s1 = [s1, s2, s3];
             s0 = s1;
           } else {
@@ -2908,39 +2910,39 @@ module.exports = (function() {
         s0 = peg$c129;
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c130); }
       }
-      if (s0 === null) {
+      if (s0 === peg$FAILED) {
         if (input.substr(peg$currPos, 2) === peg$c131) {
           s0 = peg$c131;
           peg$currPos += 2;
         } else {
-          s0 = null;
+          s0 = peg$FAILED;
           if (peg$silentFails === 0) { peg$fail(peg$c132); }
         }
-        if (s0 === null) {
+        if (s0 === peg$FAILED) {
           if (input.charCodeAt(peg$currPos) === 13) {
             s0 = peg$c133;
             peg$currPos++;
           } else {
-            s0 = null;
+            s0 = peg$FAILED;
             if (peg$silentFails === 0) { peg$fail(peg$c134); }
           }
-          if (s0 === null) {
+          if (s0 === peg$FAILED) {
             if (input.charCodeAt(peg$currPos) === 8232) {
               s0 = peg$c135;
               peg$currPos++;
             } else {
-              s0 = null;
+              s0 = peg$FAILED;
               if (peg$silentFails === 0) { peg$fail(peg$c136); }
             }
-            if (s0 === null) {
+            if (s0 === peg$FAILED) {
               if (input.charCodeAt(peg$currPos) === 8233) {
                 s0 = peg$c137;
                 peg$currPos++;
               } else {
-                s0 = null;
+                s0 = peg$FAILED;
                 if (peg$silentFails === 0) { peg$fail(peg$c138); }
               }
             }
@@ -2948,8 +2950,8 @@ module.exports = (function() {
         }
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c128); }
       }
 
@@ -2963,7 +2965,7 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c140); }
       }
 
@@ -2978,12 +2980,12 @@ module.exports = (function() {
         s0 = input.charAt(peg$currPos);
         peg$currPos++;
       } else {
-        s0 = null;
+        s0 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c143); }
       }
       peg$silentFails--;
-      if (s0 === null) {
-        s1 = null;
+      if (s0 === peg$FAILED) {
+        s1 = peg$FAILED;
         if (peg$silentFails === 0) { peg$fail(peg$c141); }
       }
 
@@ -2996,7 +2998,7 @@ module.exports = (function() {
 
     peg$result = peg$startRuleFunction();
 
-    if (peg$result !== null && peg$currPos === input.length) {
+    if (peg$result !== peg$FAILED && peg$currPos === input.length) {
       return peg$result;
     } else {
       peg$cleanupExpected(peg$maxFailExpected);
diff --git a/spec/compiler/passes/generate-bytecode.spec.js b/spec/compiler/passes/generate-bytecode.spec.js
index dd9d0d4..829b78b 100644
--- a/spec/compiler/passes/generate-bytecode.spec.js
+++ b/spec/compiler/passes/generate-bytecode.spec.js
@@ -163,7 +163,7 @@ describe("compiler pass |generateBytecode|", function() {
 
       it("defines correct constants", function() {
         expect(pass).toChangeAST(grammar, constsDetails([
-          'null',
+          'peg$FAILED',
           '"a"',
           '{ type: "literal", value: "a", description: "\\"a\\"" }',
           '"b"',
@@ -219,7 +219,7 @@ describe("compiler pass |generateBytecode|", function() {
 
       it("defines correct constants", function() {
         expect(pass).toChangeAST(grammar, constsDetails([
-          'null',
+          'peg$FAILED',
           '"a"',
           '{ type: "literal", value: "a", description: "\\"a\\"" }',
           '"b"',
@@ -273,7 +273,7 @@ describe("compiler pass |generateBytecode|", function() {
     it("defines correct constants", function() {
       expect(pass).toChangeAST(grammar, constsDetails([
         '""',
-        'null',
+        'peg$FAILED',
         '"a"',
         '{ type: "literal", value: "a", description: "\\"a\\"" }'
       ]));
@@ -302,7 +302,7 @@ describe("compiler pass |generateBytecode|", function() {
     it("defines correct constants", function() {
       expect(pass).toChangeAST(grammar, constsDetails([
         '""',
-        'null',
+        'peg$FAILED',
         '"a"',
         '{ type: "literal", value: "a", description: "\\"a\\"" }'
       ]));
@@ -328,7 +328,7 @@ describe("compiler pass |generateBytecode|", function() {
       it("defines correct constants", function() {
         expect(pass).toChangeAST(
           grammar,
-          constsDetails(['function() { code }', '""', 'null'])
+          constsDetails(['function() { code }', '""', 'peg$FAILED'])
         );
       });
     });
@@ -372,7 +372,7 @@ describe("compiler pass |generateBytecode|", function() {
 
       it("defines correct constants", function() {
         expect(pass).toChangeAST(grammar, constsDetails([
-          'null',
+          'peg$FAILED',
           '"a"',
           '{ type: "literal", value: "a", description: "\\"a\\"" }',
           '"b"',
@@ -405,7 +405,7 @@ describe("compiler pass |generateBytecode|", function() {
       it("defines correct constants", function() {
         expect(pass).toChangeAST(
           grammar,
-          constsDetails(['function() { code }', '""', 'null'])
+          constsDetails(['function() { code }', '""', 'peg$FAILED'])
         );
       });
     });
@@ -449,7 +449,7 @@ describe("compiler pass |generateBytecode|", function() {
 
       it("defines correct constants", function() {
         expect(pass).toChangeAST(grammar, constsDetails([
-          'null',
+          'peg$FAILED',
           '"a"',
           '{ type: "literal", value: "a", description: "\\"a\\"" }',
           '"b"',
@@ -528,7 +528,7 @@ describe("compiler pass |generateBytecode|", function() {
     it("defines correct constants", function() {
       expect(pass).toChangeAST(grammar, constsDetails([
         '[]',
-        'null',
+        'peg$FAILED',
         '"a"',
         '{ type: "literal", value: "a", description: "\\"a\\"" }'
       ]));
diff --git a/spec/generated-parser.spec.js b/spec/generated-parser.spec.js
index 71eb211..f1912d4 100644
--- a/spec/generated-parser.spec.js
+++ b/spec/generated-parser.spec.js
@@ -266,18 +266,12 @@ describe("generated parser", function() {
     });
 
     describe("action code", function() {
-      it("tranforms the expression result by returnung a non-|null| value", function() {
+      it("tranforms the expression result by returnung a value", function() {
         var parser = PEG.buildParser('start = "a" { return 42; }', options);
 
         expect(parser).toParse("a", 42);
       });
 
-      it("causes match failure by returning |null|", function() {
-        var parser = PEG.buildParser('start = "a" { return null; }', options);
-
-        expect(parser).toFailToParse("a");
-      });
-
       it("is not called when the expression does not match", function() {
         var parser = PEG.buildParser(
               'start = "a" { throw "Boom!"; } / "b"',
@@ -360,15 +354,6 @@ describe("generated parser", function() {
 
         expect(parser).toParse("a", { a: 42 }, { a: 42 });
       });
-
-      it("does not advance position when the expression matches but the action returns |null|", function() {
-        var parser = PEG.buildParser(
-              'start = "a" { return null; } / "a"',
-              options
-            );
-
-        expect(parser).toParse("a", "a");
-      });
     });
 
     describe("sequence matching", function() {