diff --git a/benchmark/index.js b/benchmark/index.js
index 0bd78e7..03ae562 100644
--- a/benchmark/index.js
+++ b/benchmark/index.js
@@ -72,7 +72,7 @@ $("#run").click(() => {
   }
 
   Runner.run(benchmarks, runCount, options, {
-    readFile: function(file) {
+    readFile(file) {
       return $.ajax({
         type: "GET",
         url: file,
@@ -81,11 +81,11 @@ $("#run").click(() => {
       }).responseText;
     },
 
-    testStart: function() {
+    testStart() {
       // Nothing to do.
     },
 
-    testFinish: function(benchmark, test, inputSize, parseTime) {
+    testFinish(benchmark, test, inputSize, parseTime) {
       appendResult(
         "individual",
         test.title,
@@ -95,11 +95,11 @@ $("#run").click(() => {
       );
     },
 
-    benchmarkStart: function(benchmark) {
+    benchmarkStart(benchmark) {
       appendHeading(benchmark.title);
     },
 
-    benchmarkFinish: function(benchmark, inputSize, parseTime) {
+    benchmarkFinish(benchmark, inputSize, parseTime) {
       appendResult(
         "benchmark-total",
         benchmark.title + " total",
@@ -109,14 +109,14 @@ $("#run").click(() => {
       );
     },
 
-    start: function() {
+    start() {
       $("#run-count, #cache, #run").attr("disabled", "disabled");
 
       resultsTable.show();
       $("#results-table tr").slice(1).remove();
     },
 
-    finish: function(inputSize, parseTime) {
+    finish(inputSize, parseTime) {
       appendResult(
         "total",
         "Total",
diff --git a/benchmark/run b/benchmark/run
index 8071a75..6f60592 100755
--- a/benchmark/run
+++ b/benchmark/run
@@ -163,32 +163,32 @@ if (args.length > 0) {
 }
 
 Runner.run(benchmarks, runCount, options, {
-  readFile: function(file) {
+  readFile(file) {
     return fs.readFileSync(__dirname + "/" + file, "utf8");
   },
 
-  testStart: function() {
+  testStart() {
     // Nothing to do.
   },
 
-  testFinish: function(benchmark, test, inputSize, parseTime) {
+  testFinish(benchmark, test, inputSize, parseTime) {
     writeResult(test.title, inputSize, parseTime);
   },
 
-  benchmarkStart: function(benchmark) {
+  benchmarkStart(benchmark) {
     writeHeading(benchmark.title);
   },
 
-  benchmarkFinish: function(benchmark, inputSize, parseTime) {
+  benchmarkFinish(benchmark, inputSize, parseTime) {
     writeSeparator();
     writeResult(benchmark.title + " total", inputSize, parseTime);
   },
 
-  start: function() {
+  start() {
     writeTableHeader();
   },
 
-  finish: function(inputSize, parseTime) {
+  finish(inputSize, parseTime) {
     writeSeparator();
     writeResult("Total", inputSize, parseTime);
     writeTableFooter();
diff --git a/benchmark/runner.js b/benchmark/runner.js
index b885851..861bf7a 100644
--- a/benchmark/runner.js
+++ b/benchmark/runner.js
@@ -5,17 +5,17 @@
 let peg = require("../lib/peg");
 
 let Runner = {
-  run: function(benchmarks, runCount, options, callbacks) {
+  run(benchmarks, runCount, options, callbacks) {
     // Queue
 
     let Q = {
       functions: [],
 
-      add: function(f) {
+      add(f) {
         this.functions.push(f);
       },
 
-      run: function() {
+      run() {
         if (this.functions.length > 0) {
           this.functions.shift()();
 
diff --git a/lib/compiler/asts.js b/lib/compiler/asts.js
index cfb1f72..e7f383a 100644
--- a/lib/compiler/asts.js
+++ b/lib/compiler/asts.js
@@ -4,7 +4,7 @@ let visitor = require("./visitor");
 
 // AST utilities.
 let asts = {
-  findRule: function(ast, name) {
+  findRule(ast, name) {
     for (let i = 0; i < ast.rules.length; i++) {
       if (ast.rules[i].name === name) {
         return ast.rules[i];
@@ -14,7 +14,7 @@ let asts = {
     return undefined;
   },
 
-  indexOfRule: function(ast, name) {
+  indexOfRule(ast, name) {
     for (let i = 0; i < ast.rules.length; i++) {
       if (ast.rules[i].name === name) {
         return i;
@@ -24,7 +24,7 @@ let asts = {
     return -1;
   },
 
-  alwaysConsumesOnSuccess: function(ast, node) {
+  alwaysConsumesOnSuccess(ast, node) {
     function consumesTrue()  { return true;  }
     function consumesFalse() { return false; }
 
@@ -36,13 +36,13 @@ let asts = {
       rule: consumesExpression,
       named: consumesExpression,
 
-      choice: function(node) {
+      choice(node) {
         return node.alternatives.every(consumes);
       },
 
       action: consumesExpression,
 
-      sequence: function(node) {
+      sequence(node) {
         return node.elements.some(consumes);
       },
 
@@ -57,11 +57,11 @@ let asts = {
       semantic_and: consumesFalse,
       semantic_not: consumesFalse,
 
-      rule_ref: function(node) {
+      rule_ref(node) {
         return consumes(asts.findRule(ast, node.name));
       },
 
-      literal: function(node) {
+      literal(node) {
         return node.value !== "";
       },
 
diff --git a/lib/compiler/index.js b/lib/compiler/index.js
index e763fa2..c1f383a 100644
--- a/lib/compiler/index.js
+++ b/lib/compiler/index.js
@@ -47,7 +47,7 @@ let compiler = {
   // if the AST contains a semantic error. Note that not all errors are detected
   // during the generation and some may protrude to the generated parser and
   // cause its malfunction.
-  compile: function(ast, passes, options) {
+  compile(ast, passes, options) {
     options = options !== undefined ? options : {};
 
     options = processOptions(options, {
diff --git a/lib/compiler/js.js b/lib/compiler/js.js
index afe2ee1..5a2bea4 100644
--- a/lib/compiler/js.js
+++ b/lib/compiler/js.js
@@ -4,7 +4,7 @@ function hex(ch) { return ch.charCodeAt(0).toString(16).toUpperCase(); }
 
 // JavaScript code generation helpers.
 let js = {
-  stringEscape: function(s) {
+  stringEscape(s) {
     // ECMA-262, 5th ed., 7.8.4: All characters may appear literally in a string
     // literal except for the closing quote character, backslash, carriage
     // return, line separator, paragraph separator, and line feed. Any character
@@ -27,7 +27,7 @@ let js = {
       .replace(/[\u1000-\uFFFF]/g,      ch => "\\u"  + hex(ch));
   },
 
-  regexpClassEscape: function(s) {
+  regexpClassEscape(s) {
     // Based on ECMA-262, 5th ed., 7.8.5 & 15.10.1.
     //
     // For portability, we also escape all control and non-ASCII characters.
diff --git a/lib/compiler/passes/generate-bytecode.js b/lib/compiler/passes/generate-bytecode.js
index fdebde4..d944f28 100644
--- a/lib/compiler/passes/generate-bytecode.js
+++ b/lib/compiler/passes/generate-bytecode.js
@@ -288,13 +288,13 @@ function generateBytecode(ast) {
   }
 
   let generate = visitor.build({
-    grammar: function(node) {
+    grammar(node) {
       node.rules.forEach(generate);
 
       node.consts = consts;
     },
 
-    rule: function(node) {
+    rule(node) {
       node.bytecode = generate(node.expression, {
         sp: -1,        // stack pointer
         env: { },      // mapping of label names to stack positions
@@ -302,7 +302,7 @@ function generateBytecode(ast) {
       });
     },
 
-    named: function(node, context) {
+    named(node, context) {
       let nameIndex = addConst(
         "peg$otherExpectation(\"" + js.stringEscape(node.name) + "\")"
       );
@@ -319,7 +319,7 @@ function generateBytecode(ast) {
       );
     },
 
-    choice: function(node, context) {
+    choice(node, context) {
       function buildAlternativesCode(alternatives, context) {
         return buildSequence(
           generate(alternatives[0], {
@@ -343,7 +343,7 @@ function generateBytecode(ast) {
       return buildAlternativesCode(node.alternatives, context);
     },
 
-    action: function(node, context) {
+    action(node, context) {
       let env = cloneEnv(context.env);
       let emitCall = node.expression.type !== "sequence"
                   || node.expression.elements.length === 0;
@@ -371,7 +371,7 @@ function generateBytecode(ast) {
         : expressionCode;
     },
 
-    sequence: function(node, context) {
+    sequence(node, context) {
       function buildElementsCode(elements, context) {
         if (elements.length > 0) {
           let processedCount = node.elements.length - elements.slice(1).length;
@@ -429,7 +429,7 @@ function generateBytecode(ast) {
       );
     },
 
-    labeled: function(node, context) {
+    labeled(node, context) {
       let env = cloneEnv(context.env);
 
       context.env[node.label] = context.sp + 1;
@@ -441,7 +441,7 @@ function generateBytecode(ast) {
       });
     },
 
-    text: function(node, context) {
+    text(node, context) {
       return buildSequence(
         [op.PUSH_CURR_POS],
         generate(node.expression, {
@@ -457,15 +457,15 @@ function generateBytecode(ast) {
       );
     },
 
-    simple_and: function(node, context) {
+    simple_and(node, context) {
       return buildSimplePredicate(node.expression, false, context);
     },
 
-    simple_not: function(node, context) {
+    simple_not(node, context) {
       return buildSimplePredicate(node.expression, true, context);
     },
 
-    optional: function(node, context) {
+    optional(node, context) {
       return buildSequence(
         generate(node.expression, {
           sp: context.sp,
@@ -480,7 +480,7 @@ function generateBytecode(ast) {
       );
     },
 
-    zero_or_more: function(node, context) {
+    zero_or_more(node, context) {
       let expressionCode = generate(node.expression, {
         sp: context.sp + 1,
         env: cloneEnv(context.env),
@@ -495,7 +495,7 @@ function generateBytecode(ast) {
       );
     },
 
-    one_or_more: function(node, context) {
+    one_or_more(node, context) {
       let expressionCode = generate(node.expression, {
         sp: context.sp + 1,
         env: cloneEnv(context.env),
@@ -513,7 +513,7 @@ function generateBytecode(ast) {
       );
     },
 
-    group: function(node, context) {
+    group(node, context) {
       return generate(node.expression, {
         sp: context.sp,
         env: cloneEnv(context.env),
@@ -521,19 +521,19 @@ function generateBytecode(ast) {
       });
     },
 
-    semantic_and: function(node, context) {
+    semantic_and(node, context) {
       return buildSemanticPredicate(node.code, false, context);
     },
 
-    semantic_not: function(node, context) {
+    semantic_not(node, context) {
       return buildSemanticPredicate(node.code, true, context);
     },
 
-    rule_ref: function(node) {
+    rule_ref(node) {
       return [op.RULE, asts.indexOfRule(ast, node.name)];
     },
 
-    literal: function(node) {
+    literal(node) {
       if (node.value.length > 0) {
         let stringIndex = addConst("\""
           + js.stringEscape(
@@ -567,7 +567,7 @@ function generateBytecode(ast) {
       }
     },
 
-    class: function(node) {
+    class(node) {
       let regexp = "/^["
         + (node.inverted ? "^" : "")
         + node.parts.map(part =>
@@ -601,7 +601,7 @@ function generateBytecode(ast) {
       );
     },
 
-    any: function() {
+    any() {
       let expectedIndex = addConst("peg$anyExpectation()");
 
       return buildCondition(
diff --git a/lib/compiler/passes/generate-js.js b/lib/compiler/passes/generate-js.js
index 4cc64a3..d0e3a69 100644
--- a/lib/compiler/passes/generate-js.js
+++ b/lib/compiler/passes/generate-js.js
@@ -414,7 +414,7 @@ function generateJS(ast, options) {
       sp: -1,
       maxSp: -1,
 
-      push: function(exprCode) {
+      push(exprCode) {
         let code = s(++this.sp) + " = " + exprCode + ";";
 
         if (this.sp > this.maxSp) { this.maxSp = this.sp; }
@@ -422,7 +422,7 @@ function generateJS(ast, options) {
         return code;
       },
 
-      pop: function(n) {
+      pop(n) {
         if (n === undefined) {
           return s(this.sp--);
         } else {
@@ -438,11 +438,11 @@ function generateJS(ast, options) {
         }
       },
 
-      top: function() {
+      top() {
         return s(this.sp);
       },
 
-      index: function(i) {
+      index(i) {
         return s(this.sp - i);
       }
     };
@@ -1223,7 +1223,7 @@ function generateJS(ast, options) {
     }
 
     let generators = {
-      bare: function() {
+      bare() {
         return [
           generateGeneratedByComment(),
           "(function() {",
@@ -1236,7 +1236,7 @@ function generateJS(ast, options) {
         ].join("\n");
       },
 
-      commonjs: function() {
+      commonjs() {
         let parts = [];
         let dependencyVars = Object.keys(options.dependencies);
 
@@ -1268,7 +1268,7 @@ function generateJS(ast, options) {
         return parts.join("\n");
       },
 
-      amd: function() {
+      amd() {
         let dependencyVars = Object.keys(options.dependencies);
         let dependencyIds = dependencyIds.map(v => options.dependencies[v]);
         let dependencies = "["
@@ -1291,7 +1291,7 @@ function generateJS(ast, options) {
         ].join("\n");
       },
 
-      globals: function() {
+      globals() {
         return [
           generateGeneratedByComment(),
           "(function(root) {",
@@ -1305,7 +1305,7 @@ function generateJS(ast, options) {
         ].join("\n");
       },
 
-      umd: function() {
+      umd() {
         let parts = [];
         let dependencyVars = Object.keys(options.dependencies);
         let dependencyIds = dependencyIds.map(v => options.dependencies[v]);
diff --git a/lib/compiler/passes/remove-proxy-rules.js b/lib/compiler/passes/remove-proxy-rules.js
index c208fe3..a95cc3c 100644
--- a/lib/compiler/passes/remove-proxy-rules.js
+++ b/lib/compiler/passes/remove-proxy-rules.js
@@ -10,7 +10,7 @@ function removeProxyRules(ast, options) {
 
   function replaceRuleRefs(ast, from, to) {
     let replace = visitor.build({
-      rule_ref: function(node) {
+      rule_ref(node) {
         if (node.name === from) {
           node.name = to;
         }
diff --git a/lib/compiler/passes/report-duplicate-labels.js b/lib/compiler/passes/report-duplicate-labels.js
index c3f4da4..1c83e56 100644
--- a/lib/compiler/passes/report-duplicate-labels.js
+++ b/lib/compiler/passes/report-duplicate-labels.js
@@ -20,11 +20,11 @@ function reportDuplicateLabels(ast) {
   }
 
   let check = visitor.build({
-    rule: function(node) {
+    rule(node) {
       check(node.expression, { });
     },
 
-    choice: function(node, env) {
+    choice(node, env) {
       node.alternatives.forEach(alternative => {
         check(alternative, cloneEnv(env));
       });
@@ -32,7 +32,7 @@ function reportDuplicateLabels(ast) {
 
     action: checkExpressionWithClonedEnv,
 
-    labeled: function(node, env) {
+    labeled(node, env) {
       if (env.hasOwnProperty(node.label)) {
         throw new GrammarError(
           "Label \"" + node.label + "\" is already defined "
diff --git a/lib/compiler/passes/report-duplicate-rules.js b/lib/compiler/passes/report-duplicate-rules.js
index 73ca831..72c3e9b 100644
--- a/lib/compiler/passes/report-duplicate-rules.js
+++ b/lib/compiler/passes/report-duplicate-rules.js
@@ -8,7 +8,7 @@ function reportDuplicateRules(ast) {
   let rules = {};
 
   let check = visitor.build({
-    rule: function(node) {
+    rule(node) {
       if (rules.hasOwnProperty(node.name)) {
         throw new GrammarError(
           "Rule \"" + node.name + "\" is already defined "
diff --git a/lib/compiler/passes/report-infinite-recursion.js b/lib/compiler/passes/report-infinite-recursion.js
index 229f0d8..d5ba312 100644
--- a/lib/compiler/passes/report-infinite-recursion.js
+++ b/lib/compiler/passes/report-infinite-recursion.js
@@ -18,13 +18,13 @@ function reportInfiniteRecursion(ast) {
   let visitedRules = [];
 
   let check = visitor.build({
-    rule: function(node) {
+    rule(node) {
       visitedRules.push(node.name);
       check(node.expression);
       visitedRules.pop(node.name);
     },
 
-    sequence: function(node) {
+    sequence(node) {
       node.elements.every(element => {
         check(element);
 
@@ -32,7 +32,7 @@ function reportInfiniteRecursion(ast) {
       });
     },
 
-    rule_ref: function(node) {
+    rule_ref(node) {
       if (visitedRules.indexOf(node.name) !== -1) {
         visitedRules.push(node.name);
 
diff --git a/lib/compiler/passes/report-infinite-repetition.js b/lib/compiler/passes/report-infinite-repetition.js
index 088a596..f521931 100644
--- a/lib/compiler/passes/report-infinite-repetition.js
+++ b/lib/compiler/passes/report-infinite-repetition.js
@@ -8,7 +8,7 @@ let visitor = require("../visitor");
 // grammar, which prevents infinite loops in the generated parser.
 function reportInfiniteRepetition(ast) {
   let check = visitor.build({
-    zero_or_more: function(node) {
+    zero_or_more(node) {
       if (!asts.alwaysConsumesOnSuccess(ast, node.expression)) {
         throw new GrammarError(
           "Possible infinite loop when parsing (repetition used with an expression that may not consume any input).",
@@ -17,7 +17,7 @@ function reportInfiniteRepetition(ast) {
       }
     },
 
-    one_or_more: function(node) {
+    one_or_more(node) {
       if (!asts.alwaysConsumesOnSuccess(ast, node.expression)) {
         throw new GrammarError(
           "Possible infinite loop when parsing (repetition used with an expression that may not consume any input).",
diff --git a/lib/compiler/passes/report-undefined-rules.js b/lib/compiler/passes/report-undefined-rules.js
index 9fd8276..0f5d941 100644
--- a/lib/compiler/passes/report-undefined-rules.js
+++ b/lib/compiler/passes/report-undefined-rules.js
@@ -7,7 +7,7 @@ let visitor = require("../visitor");
 // Checks that all referenced rules exist.
 function reportUndefinedRules(ast) {
   let check = visitor.build({
-    rule_ref: function(node) {
+    rule_ref(node) {
       if (!asts.findRule(ast, node.name)) {
         throw new GrammarError(
           "Rule \"" + node.name + "\" is not defined.",
diff --git a/lib/compiler/visitor.js b/lib/compiler/visitor.js
index 9bcf186..54446e6 100644
--- a/lib/compiler/visitor.js
+++ b/lib/compiler/visitor.js
@@ -2,7 +2,7 @@
 
 // Simple AST node visitor builder.
 let visitor = {
-  build: function(functions) {
+  build(functions) {
     function visit(node) {
       return functions[node.type].apply(null, arguments);
     }
@@ -26,7 +26,7 @@ let visitor = {
     }
 
     const DEFAULT_FUNCTIONS = {
-      grammar: function(node) {
+      grammar(node) {
         let extraArgs = Array.prototype.slice.call(arguments, 1);
 
         if (node.initializer) {
diff --git a/lib/peg.js b/lib/peg.js
index 39ac51a..9dfb7b0 100644
--- a/lib/peg.js
+++ b/lib/peg.js
@@ -17,7 +17,7 @@ let peg = {
   // |peg.GrammarError| if it contains a semantic error. Note that not all
   // errors are detected during the generation and some may protrude to the
   // generated parser and cause its malfunction.
-  generate: function(grammar, options) {
+  generate(grammar, options) {
     options = options !== undefined ? options : {};
 
     function convertPasses(passes) {
diff --git a/spec/api/plugin-api.spec.js b/spec/api/plugin-api.spec.js
index 56db185..8646e38 100644
--- a/spec/api/plugin-api.spec.js
+++ b/spec/api/plugin-api.spec.js
@@ -5,7 +5,7 @@ let peg = require("../../lib/peg");
 describe("plugin API", function() {
   beforeEach(function() {
     this.addMatchers({
-      toBeObject: function() {
+      toBeObject() {
         this.message = () =>
           "Expected " + jasmine.pp(this.actual) + " "
             + (this.isNot ? "not " : "")
@@ -14,7 +14,7 @@ describe("plugin API", function() {
         return this.actual !== null && typeof this.actual === "object";
       },
 
-      toBeArray: function() {
+      toBeArray() {
         this.message = () =>
           "Expected " + jasmine.pp(this.actual) + " "
             + (this.isNot ? "not " : "")
@@ -23,7 +23,7 @@ describe("plugin API", function() {
         return Object.prototype.toString.apply(this.actual) === "[object Array]";
       },
 
-      toBeFunction: function() {
+      toBeFunction() {
         this.message = () =>
           "Expected " + jasmine.pp(this.actual) + " "
             + (this.isNot ? "not " : "")
@@ -40,9 +40,9 @@ describe("plugin API", function() {
     it("is called for each plugin", function() {
       let pluginsUsed = [false, false, false];
       let plugins = [
-        { use: function() { pluginsUsed[0] = true; } },
-        { use: function() { pluginsUsed[1] = true; } },
-        { use: function() { pluginsUsed[2] = true; } }
+        { use() { pluginsUsed[0] = true; } },
+        { use() { pluginsUsed[1] = true; } },
+        { use() { pluginsUsed[2] = true; } }
       ];
 
       peg.generate(grammar, { plugins: plugins });
@@ -52,7 +52,7 @@ describe("plugin API", function() {
 
     it("receives configuration", function() {
       let plugin = {
-        use: function(config) {
+        use(config) {
           expect(config).toBeObject();
 
           expect(config.parser).toBeObject();
@@ -82,7 +82,7 @@ describe("plugin API", function() {
 
     it("receives options", function() {
       let plugin = {
-        use: function(config, options) {
+        use(config, options) {
           expect(options).toEqual(generateOptions);
         }
       };
@@ -93,7 +93,7 @@ describe("plugin API", function() {
 
     it("can replace parser", function() {
       let plugin = {
-        use: function(config) {
+        use(config) {
           let parser = peg.generate([
             "start = .* {",
             "  return {",
@@ -119,7 +119,7 @@ describe("plugin API", function() {
 
     it("can change compiler passes", function() {
       let plugin = {
-        use: function(config) {
+        use(config) {
           let pass = ast => {
             ast.code = "({ parse: function() { return 42; } })";
           };
@@ -139,7 +139,7 @@ describe("plugin API", function() {
         "c = 'x'"
       ].join("\n");
       let plugin = {
-        use: function(config, options) {
+        use(config, options) {
           options.allowedStartRules = ["b", "c"];
         }
       };
diff --git a/spec/behavior/generated-parser-behavior.spec.js b/spec/behavior/generated-parser-behavior.spec.js
index 23656bd..c3bbcd8 100644
--- a/spec/behavior/generated-parser-behavior.spec.js
+++ b/spec/behavior/generated-parser-behavior.spec.js
@@ -38,7 +38,7 @@ describe("generated parser behavior", function() {
 
   beforeEach(function() {
     this.addMatchers({
-      toParse: function(input, expected, options) {
+      toParse(input, expected, options) {
         options = options !== undefined ? options : {};
 
         let result;
@@ -70,7 +70,7 @@ describe("generated parser behavior", function() {
         }
       },
 
-      toFailToParse: function(input, details, options) {
+      toFailToParse(input, details, options) {
         options = options !== undefined ? options : {};
 
         let result;
diff --git a/spec/unit/compiler/passes/helpers.js b/spec/unit/compiler/passes/helpers.js
index b622127..8d07551 100644
--- a/spec/unit/compiler/passes/helpers.js
+++ b/spec/unit/compiler/passes/helpers.js
@@ -4,7 +4,7 @@ let peg = require("../../../../lib/peg");
 
 beforeEach(function() {
   this.addMatchers({
-    toChangeAST: function(grammar, details, options) {
+    toChangeAST(grammar, details, options) {
       options = options !== undefined ? options : {};
 
       function matchDetails(value, details) {
@@ -58,7 +58,7 @@ beforeEach(function() {
       return matchDetails(ast, details);
     },
 
-    toReportError: function(grammar, details) {
+    toReportError(grammar, details) {
       let ast = peg.parser.parse(grammar);
 
       try {
diff --git a/spec/unit/parser.spec.js b/spec/unit/parser.spec.js
index 10a2859..04bcc9c 100644
--- a/spec/unit/parser.spec.js
+++ b/spec/unit/parser.spec.js
@@ -129,7 +129,7 @@ describe("PEG.js grammar parser", function() {
     }
 
     let strip = buildVisitor({
-      grammar: function(node) {
+      grammar(node) {
         delete node.location;
 
         if (node.initializer) {
@@ -165,7 +165,7 @@ describe("PEG.js grammar parser", function() {
 
   beforeEach(function() {
     this.addMatchers({
-      toParseAs: function(expected) {
+      toParseAs(expected) {
         let result;
 
         try {
@@ -191,7 +191,7 @@ describe("PEG.js grammar parser", function() {
         return this.env.equals_(result, expected);
       },
 
-      toFailToParse: function(details) {
+      toFailToParse(details) {
         let result;
 
         try {