From c20f719a22995393665096c3bd6888d0103bec63 Mon Sep 17 00:00:00 2001
From: Daniel Wang <daniel.liberated@gmail.com>
Date: Wed, 15 May 2019 00:29:03 +0800
Subject: [PATCH] T223296

---
 lib/compiler/asts.js               |   2 +
 lib/compiler/passes/ast-to-code.js |  28 +++-
 lib/compiler/traverser.js          |   2 +
 lib/compiler/visitor.js            |   2 +
 lib/parser.js                      | 218 ++++++++++++++++-------------
 lib/parser.pegjs                   |   6 +-
 6 files changed, 154 insertions(+), 104 deletions(-)

diff --git a/lib/compiler/asts.js b/lib/compiler/asts.js
index fa68f67..6266705 100644
--- a/lib/compiler/asts.js
+++ b/lib/compiler/asts.js
@@ -44,6 +44,8 @@ var asts = {
       text:         matchesExpression,
       simple_and:   matchesTrue,
       simple_not:   matchesTrue,
+      discarded_and:matchesTrue,
+      discarded_not:matchesTrue,
       optional:     matchesTrue,
       zero_or_more: matchesTrue,
       one_or_more:  matchesExpression,
diff --git a/lib/compiler/passes/ast-to-code.js b/lib/compiler/passes/ast-to-code.js
index 015d6ca..a486ea2 100644
--- a/lib/compiler/passes/ast-to-code.js
+++ b/lib/compiler/passes/ast-to-code.js
@@ -271,6 +271,7 @@ function generateJavascript(ast, options) {
     this.failBlock = [];
     this.epilogue = [];
     this.free = [];
+    this.discarded = false;
   }
   Result.prototype = {
     /**
@@ -554,11 +555,11 @@ function generateJavascript(ast, options) {
   }
 
   /**
-   * Handler for simple_and and simple_not.
+   * Handler for simple_and, simple_not, discarded_and and discarded_not.
    */
   function buildSimplePredicate(node, context) {
     var result = new Result();
-    var negate = node.type === 'simple_not';
+    var negate = (node.type === 'simple_not') || (node.type === 'discarded_not');
     var posReg = allocPosReg();
     var reg = context.getResultReg(result);
     result.block = [`${posReg} = ${language.currPos};`];
@@ -579,6 +580,15 @@ function generateJavascript(ast, options) {
     return result;
   }
 
+  /**
+   * Handler for discarded_and and discarded_not.
+   */
+  function buildDiscardedPredicate(node, context) {
+    var result = buildSimplePredicate(node, context);
+    result.discarded = true;
+    return result;
+  }
+
   /**
    * Handler for semantic_and and semantic_not
    */
@@ -1030,7 +1040,9 @@ function generateJavascript(ast, options) {
           var subresult = recurse(node.elements[i], context.noPassThru());
           subresult.free = [];
           result.append(subresult);
-          parts.push(subresult.expression);
+          if (!subresult.discarded) {
+            parts.push(subresult.expression);
+          }
 
           // On failure, backtrack to the start of the sequence. If this is
           // the first element of the sequence, it's not necessary to backtrack
@@ -1048,7 +1060,13 @@ function generateJavascript(ast, options) {
         if (context.getDiscard()) {
           result.block.push(`${resultReg} = true;`);
         } else {
-          result.block.push(`${resultReg} = [${parts.join(',')}];`);
+          if (parts.length > 1) {
+            result.block.push(`${resultReg} = [${parts.join(',')}];`);
+          } else if (parts.length === 1) {
+            result.block.push(`${resultReg} = ${parts[0]};`);
+          } else {
+            result.block.push(`${resultReg} = true;`);
+          }
         }
         result.block.push(language.blockEnd(label));
         result.expression = resultReg;
@@ -1097,6 +1115,8 @@ function generateJavascript(ast, options) {
 
     simple_and: buildSimplePredicate,
     simple_not: buildSimplePredicate,
+    discarded_and: buildDiscardedPredicate,
+    discarded_not: buildDiscardedPredicate,
 
     optional: function(node, context) {
       var result = new Result();
diff --git a/lib/compiler/traverser.js b/lib/compiler/traverser.js
index 7100339..7051725 100644
--- a/lib/compiler/traverser.js
+++ b/lib/compiler/traverser.js
@@ -63,6 +63,8 @@ Traverser.prototype = {
     text:          traverseExpression,
     simple_and:    traverseExpression,
     simple_not:    traverseExpression,
+    discarded_and: traverseExpression,
+    discarded_not: traverseExpression,
     optional:      traverseExpression,
     zero_or_more:  traverseExpression,
     one_or_more:   traverseExpression,
diff --git a/lib/compiler/visitor.js b/lib/compiler/visitor.js
index 755bfb3..5dab54c 100644
--- a/lib/compiler/visitor.js
+++ b/lib/compiler/visitor.js
@@ -57,6 +57,8 @@ var visitor = {
       text:          visitExpression,
       simple_and:    visitExpression,
       simple_not:    visitExpression,
+      discarded_and: visitExpression,
+      discarded_not: visitExpression,
       optional:      visitExpression,
       zero_or_more:  visitExpression,
       one_or_more:   visitExpression,
diff --git a/lib/parser.js b/lib/parser.js
index d8bf40f..f4b831a 100644
--- a/lib/parser.js
+++ b/lib/parser.js
@@ -407,54 +407,56 @@ function peg$parse(input, options = {}) {
   var peg$c47 = {"type":"literal","value":"<","description":"\"<\""};
   var peg$c48 = {"type":"literal","value":"&","description":"\"&\""};
   var peg$c49 = {"type":"literal","value":">","description":"\">\""};
-  var peg$c50 = {"type":"literal","value":"!","description":"\"!\""};
-  var peg$c51 = {"type":"literal","value":"(","description":"\"(\""};
-  var peg$c52 = {"type":"literal","value":")","description":"\")\""};
-  var peg$c53 = {"type":"literal","value":"?","description":"\"?\""};
-  var peg$c54 = {"type":"literal","value":"*","description":"\"*\""};
-  var peg$c55 = {"type":"literal","value":"+","description":"\"+\""};
-  var peg$c56 = {"type":"literal","value":"null","description":"\"null\""};
-  var peg$c57 = {"type":"other","description":"literal"};
-  var peg$c58 = {"type":"other","description":"character class"};
-  var peg$c59 = {"type":"literal","value":".","description":"\".\""};
-  var peg$c60 = {"type":"literal","value":"break","description":"\"break\""};
-  var peg$c61 = {"type":"literal","value":"case","description":"\"case\""};
-  var peg$c62 = {"type":"literal","value":"catch","description":"\"catch\""};
-  var peg$c63 = {"type":"literal","value":"continue","description":"\"continue\""};
-  var peg$c64 = {"type":"literal","value":"debugger","description":"\"debugger\""};
-  var peg$c65 = {"type":"literal","value":"default","description":"\"default\""};
-  var peg$c66 = {"type":"literal","value":"delete","description":"\"delete\""};
-  var peg$c67 = {"type":"literal","value":"do","description":"\"do\""};
-  var peg$c68 = {"type":"literal","value":"else","description":"\"else\""};
-  var peg$c69 = {"type":"literal","value":"finally","description":"\"finally\""};
-  var peg$c70 = {"type":"literal","value":"for","description":"\"for\""};
-  var peg$c71 = {"type":"literal","value":"function","description":"\"function\""};
-  var peg$c72 = {"type":"literal","value":"if","description":"\"if\""};
-  var peg$c73 = {"type":"literal","value":"instanceof","description":"\"instanceof\""};
-  var peg$c74 = {"type":"literal","value":"in","description":"\"in\""};
-  var peg$c75 = {"type":"literal","value":"new","description":"\"new\""};
-  var peg$c76 = {"type":"literal","value":"return","description":"\"return\""};
-  var peg$c77 = {"type":"literal","value":"switch","description":"\"switch\""};
-  var peg$c78 = {"type":"literal","value":"this","description":"\"this\""};
-  var peg$c79 = {"type":"literal","value":"throw","description":"\"throw\""};
-  var peg$c80 = {"type":"literal","value":"try","description":"\"try\""};
-  var peg$c81 = {"type":"literal","value":"typeof","description":"\"typeof\""};
-  var peg$c82 = {"type":"literal","value":"var","description":"\"var\""};
-  var peg$c83 = {"type":"literal","value":"void","description":"\"void\""};
-  var peg$c84 = {"type":"literal","value":"while","description":"\"while\""};
-  var peg$c85 = {"type":"literal","value":"with","description":"\"with\""};
-  var peg$c86 = {"type":"literal","value":"class","description":"\"class\""};
-  var peg$c87 = {"type":"literal","value":"const","description":"\"const\""};
-  var peg$c88 = {"type":"literal","value":"enum","description":"\"enum\""};
-  var peg$c89 = {"type":"literal","value":"export","description":"\"export\""};
-  var peg$c90 = {"type":"literal","value":"extends","description":"\"extends\""};
-  var peg$c91 = {"type":"literal","value":"import","description":"\"import\""};
-  var peg$c92 = {"type":"literal","value":"super","description":"\"super\""};
-  var peg$c93 = {"type":"literal","value":"true","description":"\"true\""};
-  var peg$c94 = {"type":"literal","value":"false","description":"\"false\""};
-  var peg$c95 = {"type":"literal","value":"-","description":"\"-\""};
-  var peg$c96 = {"type":"literal","value":",","description":"\",\""};
-  var peg$c97 = {"type":"literal","value":"++","description":"\"++\""};
+  var peg$c50 = {"type":"literal","value":"&?","description":"\"&?\""};
+  var peg$c51 = {"type":"literal","value":"!?","description":"\"!?\""};
+  var peg$c52 = {"type":"literal","value":"!","description":"\"!\""};
+  var peg$c53 = {"type":"literal","value":"(","description":"\"(\""};
+  var peg$c54 = {"type":"literal","value":")","description":"\")\""};
+  var peg$c55 = {"type":"literal","value":"?","description":"\"?\""};
+  var peg$c56 = {"type":"literal","value":"*","description":"\"*\""};
+  var peg$c57 = {"type":"literal","value":"+","description":"\"+\""};
+  var peg$c58 = {"type":"literal","value":"null","description":"\"null\""};
+  var peg$c59 = {"type":"other","description":"literal"};
+  var peg$c60 = {"type":"other","description":"character class"};
+  var peg$c61 = {"type":"literal","value":".","description":"\".\""};
+  var peg$c62 = {"type":"literal","value":"break","description":"\"break\""};
+  var peg$c63 = {"type":"literal","value":"case","description":"\"case\""};
+  var peg$c64 = {"type":"literal","value":"catch","description":"\"catch\""};
+  var peg$c65 = {"type":"literal","value":"continue","description":"\"continue\""};
+  var peg$c66 = {"type":"literal","value":"debugger","description":"\"debugger\""};
+  var peg$c67 = {"type":"literal","value":"default","description":"\"default\""};
+  var peg$c68 = {"type":"literal","value":"delete","description":"\"delete\""};
+  var peg$c69 = {"type":"literal","value":"do","description":"\"do\""};
+  var peg$c70 = {"type":"literal","value":"else","description":"\"else\""};
+  var peg$c71 = {"type":"literal","value":"finally","description":"\"finally\""};
+  var peg$c72 = {"type":"literal","value":"for","description":"\"for\""};
+  var peg$c73 = {"type":"literal","value":"function","description":"\"function\""};
+  var peg$c74 = {"type":"literal","value":"if","description":"\"if\""};
+  var peg$c75 = {"type":"literal","value":"instanceof","description":"\"instanceof\""};
+  var peg$c76 = {"type":"literal","value":"in","description":"\"in\""};
+  var peg$c77 = {"type":"literal","value":"new","description":"\"new\""};
+  var peg$c78 = {"type":"literal","value":"return","description":"\"return\""};
+  var peg$c79 = {"type":"literal","value":"switch","description":"\"switch\""};
+  var peg$c80 = {"type":"literal","value":"this","description":"\"this\""};
+  var peg$c81 = {"type":"literal","value":"throw","description":"\"throw\""};
+  var peg$c82 = {"type":"literal","value":"try","description":"\"try\""};
+  var peg$c83 = {"type":"literal","value":"typeof","description":"\"typeof\""};
+  var peg$c84 = {"type":"literal","value":"var","description":"\"var\""};
+  var peg$c85 = {"type":"literal","value":"void","description":"\"void\""};
+  var peg$c86 = {"type":"literal","value":"while","description":"\"while\""};
+  var peg$c87 = {"type":"literal","value":"with","description":"\"with\""};
+  var peg$c88 = {"type":"literal","value":"class","description":"\"class\""};
+  var peg$c89 = {"type":"literal","value":"const","description":"\"const\""};
+  var peg$c90 = {"type":"literal","value":"enum","description":"\"enum\""};
+  var peg$c91 = {"type":"literal","value":"export","description":"\"export\""};
+  var peg$c92 = {"type":"literal","value":"extends","description":"\"extends\""};
+  var peg$c93 = {"type":"literal","value":"import","description":"\"import\""};
+  var peg$c94 = {"type":"literal","value":"super","description":"\"super\""};
+  var peg$c95 = {"type":"literal","value":"true","description":"\"true\""};
+  var peg$c96 = {"type":"literal","value":"false","description":"\"false\""};
+  var peg$c97 = {"type":"literal","value":"-","description":"\"-\""};
+  var peg$c98 = {"type":"literal","value":",","description":"\",\""};
+  var peg$c99 = {"type":"literal","value":"++","description":"\"++\""};
 
   // actions
   function peg$a0(initializer, rules) {
@@ -750,7 +752,9 @@ function peg$parse(input, options = {}) {
     var OPS_TO_PREFIXED_TYPES = {
       "$": "text",
       "&": "simple_and",
-      "!": "simple_not"
+      "!": "simple_not",
+      "&?": "discarded_and",
+      "!?": "discarded_not"
     };
   
     var OPS_TO_SUFFIXED_TYPES = {
@@ -3209,6 +3213,22 @@ function peg$parse(input, options = {}) {
       if (!silence) {peg$fail(peg$c16);}
       r1 = peg$FAILED;
     }
+    r1 = input.substr(peg$currPos,2);
+    if (r1 === "&?") {
+      peg$currPos += 2;
+      break choice_1;
+    } else {
+      if (!silence) {peg$fail(peg$c50);}
+      r1 = peg$FAILED;
+    }
+    r1 = input.substr(peg$currPos,2);
+    if (r1 === "!?") {
+      peg$currPos += 2;
+      break choice_1;
+    } else {
+      if (!silence) {peg$fail(peg$c51);}
+      r1 = peg$FAILED;
+    }
     if (input.charCodeAt(peg$currPos) === 38) {
       r1 = "&";
       peg$currPos += 1;
@@ -3221,7 +3241,7 @@ function peg$parse(input, options = {}) {
       r1 = "!";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c50);}
+      if (!silence) {peg$fail(peg$c52);}
       r1 = peg$FAILED;
     }
     } // choice_1
@@ -3412,7 +3432,7 @@ function peg$parse(input, options = {}) {
       r4 = "(";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c51);}
+      if (!silence) {peg$fail(peg$c53);}
       r4 = peg$FAILED;
       r1 = peg$FAILED;
       break seq_1;
@@ -3440,7 +3460,7 @@ function peg$parse(input, options = {}) {
       r8 = ")";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c52);}
+      if (!silence) {peg$fail(peg$c54);}
       r8 = peg$FAILED;
       peg$currPos = p3;
       r1 = peg$FAILED;
@@ -3464,7 +3484,7 @@ function peg$parse(input, options = {}) {
       peg$currPos += 1;
       break choice_1;
     } else {
-      if (!silence) {peg$fail(peg$c53);}
+      if (!silence) {peg$fail(peg$c55);}
       r1 = peg$FAILED;
     }
     if (input.charCodeAt(peg$currPos) === 42) {
@@ -3472,14 +3492,14 @@ function peg$parse(input, options = {}) {
       peg$currPos += 1;
       break choice_1;
     } else {
-      if (!silence) {peg$fail(peg$c54);}
+      if (!silence) {peg$fail(peg$c56);}
       r1 = peg$FAILED;
     }
     if (input.charCodeAt(peg$currPos) === 43) {
       r1 = "+";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c55);}
+      if (!silence) {peg$fail(peg$c57);}
       r1 = peg$FAILED;
     }
     } // choice_1
@@ -3631,7 +3651,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "null") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c56);}
+      if (!silence) {peg$fail(peg$c58);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -3689,7 +3709,7 @@ function peg$parse(input, options = {}) {
       peg$savedPos = p2;
       r1 = peg$a26(r4, r5);
     } else {
-      if (!silence) {peg$fail(peg$c57);}
+      if (!silence) {peg$fail(peg$c59);}
     }
     // free p3
     return r1;
@@ -3755,7 +3775,7 @@ function peg$parse(input, options = {}) {
       peg$savedPos = p2;
       r1 = peg$a27(r5, r6, r8);
     } else {
-      if (!silence) {peg$fail(peg$c58);}
+      if (!silence) {peg$fail(peg$c60);}
     }
     // free p3
     return r1;
@@ -3769,7 +3789,7 @@ function peg$parse(input, options = {}) {
       peg$savedPos = p2;
       r1 = peg$a28();
     } else {
-      if (!silence) {peg$fail(peg$c59);}
+      if (!silence) {peg$fail(peg$c61);}
       r1 = peg$FAILED;
     }
     return r1;
@@ -3954,7 +3974,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "break") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c60);}
+      if (!silence) {peg$fail(peg$c62);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -3984,7 +4004,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "case") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c61);}
+      if (!silence) {peg$fail(peg$c63);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4014,7 +4034,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "catch") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c62);}
+      if (!silence) {peg$fail(peg$c64);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4044,7 +4064,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "continue") {
       peg$currPos += 8;
     } else {
-      if (!silence) {peg$fail(peg$c63);}
+      if (!silence) {peg$fail(peg$c65);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4074,7 +4094,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "debugger") {
       peg$currPos += 8;
     } else {
-      if (!silence) {peg$fail(peg$c64);}
+      if (!silence) {peg$fail(peg$c66);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4104,7 +4124,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "default") {
       peg$currPos += 7;
     } else {
-      if (!silence) {peg$fail(peg$c65);}
+      if (!silence) {peg$fail(peg$c67);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4134,7 +4154,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "delete") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c66);}
+      if (!silence) {peg$fail(peg$c68);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4164,7 +4184,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "do") {
       peg$currPos += 2;
     } else {
-      if (!silence) {peg$fail(peg$c67);}
+      if (!silence) {peg$fail(peg$c69);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4194,7 +4214,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "else") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c68);}
+      if (!silence) {peg$fail(peg$c70);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4224,7 +4244,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "finally") {
       peg$currPos += 7;
     } else {
-      if (!silence) {peg$fail(peg$c69);}
+      if (!silence) {peg$fail(peg$c71);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4254,7 +4274,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "for") {
       peg$currPos += 3;
     } else {
-      if (!silence) {peg$fail(peg$c70);}
+      if (!silence) {peg$fail(peg$c72);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4284,7 +4304,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "function") {
       peg$currPos += 8;
     } else {
-      if (!silence) {peg$fail(peg$c71);}
+      if (!silence) {peg$fail(peg$c73);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4314,7 +4334,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "if") {
       peg$currPos += 2;
     } else {
-      if (!silence) {peg$fail(peg$c72);}
+      if (!silence) {peg$fail(peg$c74);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4344,7 +4364,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "instanceof") {
       peg$currPos += 10;
     } else {
-      if (!silence) {peg$fail(peg$c73);}
+      if (!silence) {peg$fail(peg$c75);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4374,7 +4394,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "in") {
       peg$currPos += 2;
     } else {
-      if (!silence) {peg$fail(peg$c74);}
+      if (!silence) {peg$fail(peg$c76);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4404,7 +4424,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "new") {
       peg$currPos += 3;
     } else {
-      if (!silence) {peg$fail(peg$c75);}
+      if (!silence) {peg$fail(peg$c77);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4434,7 +4454,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "return") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c76);}
+      if (!silence) {peg$fail(peg$c78);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4464,7 +4484,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "switch") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c77);}
+      if (!silence) {peg$fail(peg$c79);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4494,7 +4514,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "this") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c78);}
+      if (!silence) {peg$fail(peg$c80);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4524,7 +4544,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "throw") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c79);}
+      if (!silence) {peg$fail(peg$c81);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4554,7 +4574,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "try") {
       peg$currPos += 3;
     } else {
-      if (!silence) {peg$fail(peg$c80);}
+      if (!silence) {peg$fail(peg$c82);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4584,7 +4604,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "typeof") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c81);}
+      if (!silence) {peg$fail(peg$c83);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4614,7 +4634,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "var") {
       peg$currPos += 3;
     } else {
-      if (!silence) {peg$fail(peg$c82);}
+      if (!silence) {peg$fail(peg$c84);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4644,7 +4664,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "void") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c83);}
+      if (!silence) {peg$fail(peg$c85);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4674,7 +4694,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "while") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c84);}
+      if (!silence) {peg$fail(peg$c86);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4704,7 +4724,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "with") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c85);}
+      if (!silence) {peg$fail(peg$c87);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4734,7 +4754,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "class") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c86);}
+      if (!silence) {peg$fail(peg$c88);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4764,7 +4784,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "const") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c87);}
+      if (!silence) {peg$fail(peg$c89);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4794,7 +4814,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "enum") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c88);}
+      if (!silence) {peg$fail(peg$c90);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4824,7 +4844,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "export") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c89);}
+      if (!silence) {peg$fail(peg$c91);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4854,7 +4874,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "extends") {
       peg$currPos += 7;
     } else {
-      if (!silence) {peg$fail(peg$c90);}
+      if (!silence) {peg$fail(peg$c92);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4884,7 +4904,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "import") {
       peg$currPos += 6;
     } else {
-      if (!silence) {peg$fail(peg$c91);}
+      if (!silence) {peg$fail(peg$c93);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4914,7 +4934,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "super") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c92);}
+      if (!silence) {peg$fail(peg$c94);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -4981,7 +5001,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "true") {
       peg$currPos += 4;
     } else {
-      if (!silence) {peg$fail(peg$c93);}
+      if (!silence) {peg$fail(peg$c95);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -5011,7 +5031,7 @@ function peg$parse(input, options = {}) {
     if (r3 === "false") {
       peg$currPos += 5;
     } else {
-      if (!silence) {peg$fail(peg$c94);}
+      if (!silence) {peg$fail(peg$c96);}
       r3 = peg$FAILED;
       r2 = peg$FAILED;
       break seq_1;
@@ -5048,7 +5068,7 @@ function peg$parse(input, options = {}) {
       r5 = "-";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c95);}
+      if (!silence) {peg$fail(peg$c97);}
       r5 = peg$FAILED;
       peg$currPos = p3;
       r1 = peg$FAILED;
@@ -5188,7 +5208,7 @@ function peg$parse(input, options = {}) {
         r11 = ",";
         peg$currPos += 1;
       } else {
-        if (!silence) {peg$fail(peg$c96);}
+        if (!silence) {peg$fail(peg$c98);}
         r11 = peg$FAILED;
         peg$currPos = p9;
         r8 = peg$FAILED;
@@ -5343,7 +5363,7 @@ function peg$parse(input, options = {}) {
       r1 = "!";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c50);}
+      if (!silence) {peg$fail(peg$c52);}
       r1 = peg$FAILED;
     }
     } // choice_1
@@ -5364,7 +5384,7 @@ function peg$parse(input, options = {}) {
       r1 = "!";
       peg$currPos += 1;
     } else {
-      if (!silence) {peg$fail(peg$c50);}
+      if (!silence) {peg$fail(peg$c52);}
       r1 = peg$FAILED;
     }
     } // choice_1
@@ -5606,7 +5626,7 @@ function peg$parse(input, options = {}) {
       peg$savedPos = p2;
       r1 = peg$a35();
     } else {
-      if (!silence) {peg$fail(peg$c97);}
+      if (!silence) {peg$fail(peg$c99);}
       r1 = peg$FAILED;
     }
     return r1;
diff --git a/lib/parser.pegjs b/lib/parser.pegjs
index ad5a064..59fc67b 100644
--- a/lib/parser.pegjs
+++ b/lib/parser.pegjs
@@ -27,7 +27,9 @@
   var OPS_TO_PREFIXED_TYPES = {
     "$": "text",
     "&": "simple_and",
-    "!": "simple_not"
+    "!": "simple_not",
+    "&?": "discarded_and",
+    "!?": "discarded_not"
   };
 
   var OPS_TO_SUFFIXED_TYPES = {
@@ -198,6 +200,8 @@ PrefixedExpression
 
 PrefixedOperator
   = "$"
+  / "&?"
+  / "!?"
   / "&"
   / "!"