diff --git a/src/Parser.js b/src/Parser.js
index 01566cc71..47fa25038 100644
--- a/src/Parser.js
+++ b/src/Parser.js
@@ -195,7 +195,8 @@ Parser.prototype.handleInfixNodes = function (body, mode) {
             denomNode = new ParseNode("ordgroup", denomBody, mode);
         }
 
-        var value = func.handler(funcName, numerNode, denomNode);
+        var value = this.callFunction(
+            funcName, [numerNode, denomNode], null);
         return [new ParseNode(value.type, value, mode)];
     } else {
         return body;
@@ -430,11 +431,18 @@ Parser.prototype.parseImplicitGroup = function(pos, mode) {
         // Build the environment object. Arguments and other information will
         // be made available to the begin and end methods using properties.
         var env = environments[envName];
-        var args = [null, mode, envName];
+        var args = [];
         var newPos = this.parseArguments(
             begin.position, mode, "\\begin{" + envName + "}", env, args);
-        args[0] = newPos;
-        var result = env.handler.apply(this, args);
+        var context = {
+            pos: newPos,
+            mode: mode,
+            envName: envName,
+            parser: this,
+            lexer: this.lexer,
+            positions: args.pop()
+        };
+        var result = env.handler(context, args);
         var endLex = this.lexer.lex(result.position, mode);
         this.expect(endLex, "\\end");
         var end = this.parseFunction(result.position, mode);
@@ -491,10 +499,10 @@ Parser.prototype.parseFunction = function(pos, mode) {
                     this.lexer, baseGroup.position);
             }
 
-            var args = [func];
+            var args = [];
             var newPos = this.parseArguments(
                 baseGroup.result.position, mode, func, funcData, args);
-            var result = functions[func].handler.apply(this, args);
+            var result = this.callFunction(func, args, args.pop());
             return new ParseResult(
                 new ParseNode(result.type, result, mode),
                 newPos);
@@ -506,6 +514,18 @@ Parser.prototype.parseFunction = function(pos, mode) {
     }
 };
 
+/**
+ * Call a function handler with a suitable context and arguments.
+ */
+Parser.prototype.callFunction = function(name, args, positions) {
+    var context = {
+        funcName: name,
+        parser: this,
+        lexer: this.lexer,
+        positions: positions
+    };
+    return functions[name].handler(context, args);
+};
 
 /**
  * Parses the arguments of a function or environment
diff --git a/src/environments.js b/src/environments.js
index c323d433e..71a866c9d 100644
--- a/src/environments.js
+++ b/src/environments.js
@@ -50,14 +50,17 @@ function parseArray(parser, pos, mode, result) {
  *  - numOptionalArgs: (optional) Just like for a function
  * A bare number instead of that object indicates the numArgs value.
  *
- * The handler function will receive the following arguments:
+ * The handler function will receive two arguments
+ *  - context: information and references provided by the parser
+ *  - args: an array of arguments passed to \begin{name}
+ * The context contains the following properties:
  *  - pos: the current position of the parser.
  *  - mode: the current parsing mode.
  *  - envName: the name of the environment, one of the listed names.
- *  - [args]: the arguments passed to \begin.
- *  - positions: the positions associated with these arguments.
- * The handler is called with `this` referring to the parser.
- * It must return a ParseResult.
+ *  - parser: the parser object
+ *  - lexer: the lexer object
+ *  - positions: the positions associated with these arguments from args.
+ * The handler must return a ParseResult.
  */
 
 function defineEnvironment(names, props, handler) {
@@ -85,8 +88,10 @@ function defineEnvironment(names, props, handler) {
 // is part of the source2e.pdf file of LaTeX2e source documentation.
 defineEnvironment("array", {
     numArgs: 1
-}, function(pos, mode, envName, colalign, positions) {
-    var parser = this;
+}, function(context, args) {
+    var colalign = args[0];
+    var lexer = context.lexer;
+    var positions = context.positions;
     colalign = colalign.value.map ? colalign.value : [colalign];
     var cols = colalign.map(function(node) {
         var ca = node.value;
@@ -103,14 +108,14 @@ defineEnvironment("array", {
         }
         throw new ParseError(
             "Unknown column alignment: " + node.value,
-            parser.lexer, positions[1]);
+            lexer, positions[1]);
     });
     var res = {
         type: "array",
         cols: cols,
         hskipBeforeAndAfter: true // \@preamble in lttab.dtx
     };
-    res = parseArray(parser, pos, mode, res);
+    res = parseArray(context.parser, context.pos, context.mode, res);
     return res;
 });
 
@@ -124,7 +129,7 @@ defineEnvironment([
     "vmatrix",
     "Vmatrix"
 ], {
-}, function(pos, mode, envName) {
+}, function(context) {
     var delimiters = {
         "matrix": null,
         "pmatrix": ["(", ")"],
@@ -132,18 +137,18 @@ defineEnvironment([
         "Bmatrix": ["\\{", "\\}"],
         "vmatrix": ["|", "|"],
         "Vmatrix": ["\\Vert", "\\Vert"]
-    }[envName];
+    }[context.envName];
     var res = {
         type: "array",
         hskipBeforeAndAfter: false // \hskip -\arraycolsep in amsmath
     };
-    res = parseArray(this, pos, mode, res);
+    res = parseArray(context.parser, context.pos, context.mode, res);
     if (delimiters) {
         res.result = new ParseNode("leftright", {
             body: [res.result],
             left: delimiters[0],
             right: delimiters[1]
-        }, mode);
+        }, context.mode);
     }
     return res;
 });
@@ -152,7 +157,7 @@ defineEnvironment([
 // \def\arraystretch{1.2}%
 // \left\{\begin{array}{@{}l@{\quad}l@{}} … \end{array}\right.
 defineEnvironment("cases", {
-}, function(pos, mode, envName) {
+}, function(context) {
     var res = {
         type: "array",
         arraystretch: 1.2,
@@ -168,11 +173,11 @@ defineEnvironment("cases", {
             postgap: 0
         }]
     };
-    res = parseArray(this, pos, mode, res);
+    res = parseArray(context.parser, context.pos, context.mode, res);
     res.result = new ParseNode("leftright", {
         body: [res.result],
         left: "\\{",
         right: "."
-    }, mode);
+    }, context.mode);
     return res;
 });
diff --git a/src/functions.js b/src/functions.js
index 777b1096b..ee676591b 100644
--- a/src/functions.js
+++ b/src/functions.js
@@ -2,9 +2,9 @@ var utils = require("./utils");
 var ParseError = require("./ParseError");
 
 /* This file contains a list of functions that we parse, identified by
- * the calls to declareFunction.
+ * the calls to defineFunction.
  *
- * The first argument to declareFunction is a single name or a list of names.
+ * The first argument to defineFunction is a single name or a list of names.
  * All functions named in such a list will share a single implementation.
  *
  * Each declared function can have associated properties, which
@@ -58,14 +58,17 @@ var ParseError = require("./ParseError");
  *
  * The last argument is that implementation, the handler for the function(s).
  * It is called to handle these functions and their arguments.
- * Its own arguments are:
- *  - func: the text of the function
- *  - [args]: the next arguments are the arguments to the function,
- *            of which there are numArgs of them
+ * It receives two arguments:
+ *  - context contains information and references provided by the parser
+ *  - args is an array of arguments obtained from TeX input
+ * The context contains the following properties:
+ *  - funcName: the text (i.e. name) of the function, including \
+ *  - parser: the parser object
+ *  - lexer: the lexer object
  *  - positions: the positions in the overall string of the function
- *               and the arguments. Should only be used to produce
- *               error messages
- * The handler is called with `this` referring to the parser.
+ *               and the arguments.
+ * The latter three should only be used to produce error messages.
+ *
  * The function should return an object with the following keys:
  *  - type: The type of element that this is. This is then used in
  *          buildHTML/buildMathML to determine which function
@@ -99,7 +102,9 @@ function defineFunction(names, props, handler) {
 defineFunction("\\sqrt", {
     numArgs: 1,
     numOptionalArgs: 1
-}, function(func, index, body, positions) {
+}, function(context, args) {
+    var index = args[0];
+    var body = args[1];
     return {
         type: "sqrt",
         body: body,
@@ -112,7 +117,8 @@ defineFunction("\\text", {
     numArgs: 1,
     argTypes: ["text"],
     greediness: 2
-}, function(func, body) {
+}, function(context, args) {
+    var body = args[0];
     // Since the corresponding buildHTML/buildMathML function expects a
     // list of elements, we normalize for different kinds of arguments
     // TODO(emily): maybe this should be done somewhere else
@@ -135,7 +141,9 @@ defineFunction("\\color", {
     allowedInText: true,
     greediness: 3,
     argTypes: ["color", "original"]
-}, function(func, color, body) {
+}, function(context, args) {
+    var color = args[0];
+    var body = args[1];
     // Normalize the different kinds of bodies (see \text above)
     var inner;
     if (body.type === "ordgroup") {
@@ -154,7 +162,8 @@ defineFunction("\\color", {
 // An overline
 defineFunction("\\overline", {
     numArgs: 1
-}, function(func, body) {
+}, function(context, args) {
+    var body = args[0];
     return {
         type: "overline",
         body: body
@@ -166,7 +175,10 @@ defineFunction("\\rule", {
     numArgs: 2,
     numOptionalArgs: 1,
     argTypes: ["size", "size", "size"]
-}, function(func, shift, width, height) {
+}, function(context, args) {
+    var shift = args[0];
+    var width = args[1];
+    var height = args[2];
     return {
         type: "rule",
         shift: shift && shift.value,
@@ -178,7 +190,7 @@ defineFunction("\\rule", {
 // A KaTeX logo
 defineFunction("\\KaTeX", {
     numArgs: 0
-}, function(func) {
+}, function(context) {
     return {
         type: "katex"
     };
@@ -186,7 +198,8 @@ defineFunction("\\KaTeX", {
 
 defineFunction("\\phantom", {
     numArgs: 1
-}, function(func, body) {
+}, function(context, args) {
+    var body = args[0];
     var inner;
     if (body.type === "ordgroup") {
         inner = body.value;
@@ -260,7 +273,8 @@ defineFunction([
     numArgs: 1,
     allowedInText: true,
     greediness: 3
-}, function(func, body) {
+}, function(context, args) {
+    var body = args[0];
     var atoms;
     if (body.type === "ordgroup") {
         atoms = body.value;
@@ -270,7 +284,7 @@ defineFunction([
 
     return {
         type: "color",
-        color: "katex-" + func.slice(1),
+        color: "katex-" + context.funcName.slice(1),
         value: atoms
     };
 });
@@ -287,12 +301,12 @@ defineFunction([
     "\\tan","\\tanh"
 ], {
     numArgs: 0
-}, function(func) {
+}, function(context) {
     return {
         type: "op",
         limits: false,
         symbol: false,
-        body: func
+        body: context.funcName
     };
 });
 
@@ -302,12 +316,12 @@ defineFunction([
     "\\min", "\\Pr", "\\sup"
 ], {
     numArgs: 0
-}, function(func) {
+}, function(context) {
     return {
         type: "op",
         limits: true,
         symbol: false,
-        body: func
+        body: context.funcName
     };
 });
 
@@ -316,12 +330,12 @@ defineFunction([
     "\\int", "\\iint", "\\iiint", "\\oint"
 ], {
     numArgs: 0
-}, function(func) {
+}, function(context) {
     return {
         type: "op",
         limits: false,
         symbol: true,
-        body: func
+        body: context.funcName
     };
 });
 
@@ -332,12 +346,12 @@ defineFunction([
     "\\bigoplus", "\\bigodot", "\\bigsqcup", "\\smallint"
 ], {
     numArgs: 0
-}, function(func) {
+}, function(context) {
     return {
         type: "op",
         limits: true,
         symbol: true,
-        body: func
+        body: context.funcName
     };
 });
 
@@ -348,13 +362,15 @@ defineFunction([
 ], {
     numArgs: 2,
     greediness: 2
-}, function(func, numer, denom) {
+}, function(context, args) {
+    var numer = args[0];
+    var denom = args[1];
     var hasBarLine;
     var leftDelim = null;
     var rightDelim = null;
     var size = "auto";
 
-    switch (func) {
+    switch (context.funcName) {
     case "\\dfrac":
     case "\\frac":
     case "\\tfrac":
@@ -371,7 +387,7 @@ defineFunction([
         throw new Error("Unrecognized genfrac command");
     }
 
-    switch (func) {
+    switch (context.funcName) {
     case "\\dfrac":
     case "\\dbinom":
         size = "display";
@@ -397,9 +413,10 @@ defineFunction([
 defineFunction(["\\llap", "\\rlap"], {
     numArgs: 1,
     allowedInText: true
-}, function(func, body) {
+}, function(context, args) {
+    var body = args[0];
     return {
-        type: func.slice(1),
+        type: context.funcName.slice(1),
         body: body
     };
 });
@@ -413,17 +430,18 @@ defineFunction([
     "\\left", "\\right"
 ], {
     numArgs: 1
-}, function(func, delim, positions) {
+}, function(context, args) {
+    var delim = args[0];
     if (!utils.contains(delimiters, delim.value)) {
         throw new ParseError(
             "Invalid delimiter: '" + delim.value + "' after '" +
-                func + "'",
-            this.lexer, positions[1]);
+                context.funcName + "'",
+            context.lexer, context.positions[1]);
     }
 
     // \left and \right are caught somewhere in Parser.js, which is
     // why this data doesn't match what is in buildHTML.
-    if (func === "\\left" || func === "\\right") {
+    if (context.funcName === "\\left" || context.funcName === "\\right") {
         return {
             type: "leftright",
             value: delim.value
@@ -431,8 +449,8 @@ defineFunction([
     } else {
         return {
             type: "delimsizing",
-            size: delimiterSizes[func].size,
-            delimType: delimiterSizes[func].type,
+            size: delimiterSizes[context.funcName].size,
+            delimType: delimiterSizes[context.funcName].type,
             value: delim.value
         };
     }
@@ -464,7 +482,9 @@ defineFunction([
 ], {
     numArgs: 1,
     greediness: 2
-}, function (func, body) {
+}, function (context, args) {
+    var body = args[0];
+    var func = context.funcName;
     if (func in fontAliases) {
         func = fontAliases[func];
     }
@@ -483,10 +503,11 @@ defineFunction([
     // "\\widetilde", "\\widehat"
 ], {
     numArgs: 1
-}, function(func, base) {
+}, function(context, args) {
+    var base = args[0];
     return {
         type: "accent",
-        accent: func,
+        accent: context.funcName,
         base: base
     };
 });
@@ -494,9 +515,9 @@ defineFunction([
 // Infix generalized fractions
 defineFunction(["\\over", "\\choose"], {
     numArgs: 0
-}, function (func) {
+}, function (context) {
     var replaceWith;
-    switch (func) {
+    switch (context.funcName) {
     case "\\over":
         replaceWith = "\\frac";
         break;
@@ -517,7 +538,8 @@ defineFunction(["\\\\", "\\cr"], {
     numArgs: 0,
     numOptionalArgs: 1,
     argTypes: ["size"]
-}, function(func, size) {
+}, function(context, args) {
+    var size = args[0];
     return {
         type: "cr",
         size: size
@@ -528,11 +550,12 @@ defineFunction(["\\\\", "\\cr"], {
 defineFunction(["\\begin", "\\end"], {
     numArgs: 1,
     argTypes: ["text"]
-}, function(func, nameGroup, positions) {
+}, function(context, args) {
+    var nameGroup = args[0];
     if (nameGroup.type !== "ordgroup") {
         throw new ParseError(
             "Invalid environment name",
-            this.lexer, positions[1]);
+            context.lexer, context.positions[1]);
     }
     var name = "";
     for (var i = 0; i < nameGroup.value.length; ++i) {
@@ -541,6 +564,6 @@ defineFunction(["\\begin", "\\end"], {
     return {
         type: "environment",
         name: name,
-        namepos: positions[1]
+        namepos: context.positions[1]
     };
 });