diff --git a/.eslintrc.js b/.eslintrc.js
index 2a3e949..969a421 100644
--- a/.eslintrc.js
+++ b/.eslintrc.js
@@ -11,7 +11,7 @@ module.exports = {
     },
     "parserOptions": {
         "ecmaVersion": 2018,
-        "sourceType": "commonjs"
+        "sourceType": "module"
     },
     "rules": {
         "no-console": 0
diff --git a/cli.js b/cli.js
index 69f8061..d2931f7 100755
--- a/cli.js
+++ b/cli.js
@@ -79,7 +79,7 @@ const processOptions = args =>
     .map(arg => {
       const match = optionRegex.exec(arg)
       if (match) {
-        const [_, option, value] = match
+        const [, option, value] = match
         if (!value) {
           options[option] = !options[option]
         } else {
@@ -105,4 +105,4 @@ const main = argv => {
   }
 }
 
-return main(process.argv)
+main(process.argv)
diff --git a/docs/browser.e9f8be96.js b/docs/browser.e9f8be96.js
index c9dea57..ced3c09 100644
--- a/docs/browser.e9f8be96.js
+++ b/docs/browser.e9f8be96.js
@@ -1,15 +1,15 @@
 parcelRequire=function(e,r,t,n){var i,o="function"==typeof parcelRequire&&parcelRequire,u="function"==typeof require&&require;function f(t,n){if(!r[t]){if(!e[t]){var i="function"==typeof parcelRequire&&parcelRequire;if(!n&&i)return i(t,!0);if(o)return o(t,!0);if(u&&"string"==typeof t)return u(t);var c=new Error("Cannot find module '"+t+"'");throw c.code="MODULE_NOT_FOUND",c}p.resolve=function(r){return e[t][1][r]||r},p.cache={};var l=r[t]=new f.Module(t);e[t][0].call(l.exports,p,l,l.exports,this)}return r[t].exports;function p(e){return f(p.resolve(e))}}f.isParcelRequire=!0,f.Module=function(e){this.id=e,this.bundle=f,this.exports={}},f.modules=e,f.cache=r,f.parent=o,f.register=function(r,t){e[r]=[function(e,r){r.exports=t},{}]};for(var c=0;c<t.length;c++)try{f(t[c])}catch(e){i||(i=e)}if(t.length){var l=f(t[t.length-1]);"object"==typeof exports&&"undefined"!=typeof module?module.exports=l:"function"==typeof define&&define.amd?define(function(){return l}):n&&(this[n]=l)}if(parcelRequire=f,i)throw i;return f}({"p8GN":[function(require,module,exports) {
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+function t(n){return(t="function"==typeof Symbol&&"symbol"==typeof Symbol.iterator?function(t){return typeof t}:function(t){return t&&"function"==typeof Symbol&&t.constructor===Symbol&&t!==Symbol.prototype?"symbol":typeof t})(n)}function n(n,r){return!r||"object"!==t(r)&&"function"!=typeof r?e(n):r}function e(t){if(void 0===t)throw new ReferenceError("this hasn't been initialised - super() hasn't been called");return t}function r(t){return(r=Object.setPrototypeOf?Object.getPrototypeOf:function(t){return t.__proto__||Object.getPrototypeOf(t)})(t)}function o(t,n){if("function"!=typeof n&&null!==n)throw new TypeError("Super expression must either be null or a function");t.prototype=Object.create(n&&n.prototype,{constructor:{value:t,writable:!0,configurable:!0}}),n&&i(t,n)}function i(t,n){return(i=Object.setPrototypeOf||function(t,n){return t.__proto__=n,t})(t,n)}function c(t,n){if(!(t instanceof n))throw new TypeError("Cannot call a class as a function")}function a(t,n){for(var e=0;e<n.length;e++){var r=n[e];r.enumerable=r.enumerable||!1,r.configurable=!0,"value"in r&&(r.writable=!0),Object.defineProperty(t,r.key,r)}}function u(t,n,e){return n&&a(t.prototype,n),e&&a(t,e),t}var s=function(t){return t||""},f=function(){function t(n,e,r){c(this,t),this.msg=n,this.startCoordinates=e,this.endCoordinates=r}return u(t,[{key:"toString",value:function(){return this.msg}}]),t}(),d=function(t){function e(t,o){return c(this,e),n(this,r(e).call(this,"".concat(s(o.lexeme&&'at "'.concat(o.lexeme,'": '))).concat(t),o.startCoordinates,o.endCoordinates))}return o(e,f),e}(),l=function t(n){c(this,t),this.value=n},p=function(t,n,e){return new f(t,n,e)},y=function(t,n){return n.type===n.EOF?new f(t,n.startCoordinates,n.endCoordinates):new f("".concat(s(n.lexeme&&'at "'.concat(n.lexeme,'": '))).concat(t),n.startCoordinates,n.endCoordinates)},b=function(t,n){return new d(t,n)},m=function(t,n){if(t instanceof f){var e=n.lastIndexOf("\n",t.startCoordinates.index),r=e<0?0:e,o=n.substring(r,t.startCoordinates.index),i=n.substring(t.startCoordinates.index,t.endCoordinates.index),c=n.indexOf("\n",t.endCoordinates.index),a=c<0?n.length:c,u=n.substring(t.endCoordinates.index,a);return{oneLiner:"".concat(t instanceof d?"Runtime Error":"Parse Error",": ").concat(t.toString()," at ").concat(t.endCoordinates.line,":").concat(t.endCoordinates.col+1),preErrorSection:o,errorSection:i,postErrorSection:u}}return{oneLiner:"Unexpected javascript Error: ".concat(t)}};module.exports={error:p,LoxError:f,ReturnError:l,runtimeError:b,parseError:y,formatLoxError:m};
 },{}],"u74b":[function(require,module,exports) {
 function t(t,n){if(!(t instanceof n))throw new TypeError("Cannot call a class as a function")}function n(t,n){for(var e=0;e<n.length;e++){var i=n[e];i.enumerable=i.enumerable||!1,i.configurable=!0,"value"in i&&(i.writable=!0),Object.defineProperty(t,i.key,i)}}function e(t,e,i){return e&&n(t.prototype,e),i&&n(t,i),t}var i=require("./errors"),s=i.LoxError,r=function(){},o="\n  LEFT_PAREN, RIGHT_PAREN, LEFT_BRACE, RIGHT_BRACE,\n  COMMA, DOT, MINUS, PLUS, SEMICOLON, SLASH, STAR,\n\n  BANG, BANG_EQUAL,\n  EQUAL, EQUAL_EQUAL,\n  GREATER, GREATER_EQUAL,\n  LESS, LESS_EQUAL,\n\n  IDENTIFIER, STRING, NUMBER,\n\n  AND, CLASS, ELSE, FALSE, FUN, FOR, IF, NIL, OR,\n  PRINT, RETURN, SUPER, THIS, TRUE, VAR, WHILE,\n\n  EOF\n".split(",").map(function(t){return t.trim()}),h={};o.forEach(function(t,n){h[t]=n});var u={and:h.AND,class:h.CLASS,else:h.ELSE,false:h.FALSE,for:h.FOR,fun:h.FUN,if:h.IF,nil:h.NIL,or:h.OR,print:h.PRINT,return:h.RETURN,super:h.SUPER,this:h.THIS,true:h.TRUE,var:h.VAR,while:h.WHILE},c={"(":function(t){t.addToken(h.LEFT_PAREN)},")":function(t){t.addToken(h.RIGHT_PAREN)},"{":function(t){t.addToken(h.LEFT_BRACE)},"}":function(t){t.addToken(h.RIGHT_BRACE)},",":function(t){t.addToken(h.COMMA)},".":function(t){a(t.peek())?t.handleNumberLiterals():t.addToken(h.DOT)},"-":function(t){t.addToken(h.MINUS)},"+":function(t){t.addToken(h.PLUS)},";":function(t){t.addToken(h.SEMICOLON)},"/":function(t){if(t.nextMatch("/"))for(;"\n"!==t.peek()&&""!==t.peek();)t.chomp();else t.addToken(h.SLASH)},"*":function(t){t.addToken(h.STAR)},"!":function(t){t.addToken(t.nextMatch("=")?h.BANG_EQUAL:h.BANG)},"=":function(t){t.addToken(t.nextMatch("=")?h.EQUAL_EQUAL:h.EQUAL)},">":function(t){t.addToken(t.nextMatch("=")?h.GREATER_EQUAL:h.GREATER)},"<":function(t){t.addToken(t.nextMatch("=")?h.LESS_EQUAL:h.LESS)}," ":r,"\t":r,"\r":r,"\n":function(t){t.newline()},'"':function(t){t.handleStringLiterals()}},a=function(t){return/\d/.test(t)},l=function(t){return/[a-zA-Z_]/.test(t)},f=function(t){return l(t)||a(t)},d=function(){function n(e){t(this,n),this.source=e,this.length=e.length,this.tokens=[],this.startPosition=null,this.column=0,this.start=0,this.line=1,this.current=0}return e(n,null,[{key:"tokens",get:function(){return o}},{key:"tokenEnum",get:function(){return h}}]),e(n,[{key:"handleStringLiterals",value:function(){for(;'"'!==this.peek()&&""!==this.peek();)"\n"===this.peek()&&this.newline(),this.chomp();if(""===this.peek())throw new s("Unfinished string",this.startPosition,this.endPosition);this.chomp();var t=this.source.substring(this.start+1,this.current-1);this.addToken(h.STRING,t)}},{key:"handleNumberLiterals",value:function(){for(var t=!1;a(this.peek())||!t&&"."===this.peek();)"."===this.peek()&&(t=!0),this.chomp();var n=this.source.substring(this.start,this.current);this.addToken(h.NUMBER,parseFloat(n))}},{key:"handleIdentifiers",value:function(){for(;f(this.peek());)this.chomp();var t=this.source.substring(this.start,this.current);u[t]?this.addToken(u[t],t):this.addToken(h.IDENTIFIER,t)}},{key:"scanTokens",value:function(){for(;this.current<this.length;){var t=this.chomp();if(this.startPosition=new E(this.column-1,this.line,this.current-1),c[t])c[t](this);else if(a(t))this.handleNumberLiterals();else{if(!l(t))throw console.log(s),new s("Unexpected character ".concat(t),this.startPosition,new E(this.column,this.line,this.current));this.handleIdentifiers()}this.start=this.current}return this.addToken(h.EOF),this.tokens}},{key:"addToken",value:function(t){var n=arguments.length>1&&void 0!==arguments[1]?arguments[1]:null,e=this.source.substring(this.start,this.current);this.tokens.push(new k(t,e,n,new E(this.column,this.line,this.current),this.startPosition))}},{key:"increment",value:function(){this.current++,this.column++}},{key:"newline",value:function(){this.line++,this.column=0}},{key:"chomp",value:function(){return this.increment(),this.source.charAt(this.current-1)}},{key:"peek",value:function(){return this.source.charAt(this.current)}},{key:"nextMatch",value:function(t){return this.peek()===t&&(this.increment(),!0)}},{key:"endPosition",get:function(){return new E(this.column-1,this.line,this.current)}}]),n}(),E=function n(e,i,s){t(this,n),this.col=e,this.line=i,this.index=s},k=function n(e,i,s,r,o){t(this,n),this.type=e,this.lexeme=i,this.literal=s,this.startCoordinates=o,this.endCoordinates=r};module.exports=d;
 },{"./errors":"p8GN"}],"39eF":[function(require,module,exports) {
-function t(n){return(t="function"==typeof Symbol&&"symbol"==typeof Symbol.iterator?function(t){return typeof t}:function(t){return t&&"function"==typeof Symbol&&t.constructor===Symbol&&t!==Symbol.prototype?"symbol":typeof t})(n)}function n(n,e){return!e||"object"!==t(e)&&"function"!=typeof e?i(n):e}function i(t){if(void 0===t)throw new ReferenceError("this hasn't been initialised - super() hasn't been called");return t}function e(t){return(e=Object.setPrototypeOf?Object.getPrototypeOf:function(t){return t.__proto__||Object.getPrototypeOf(t)})(t)}function o(t,n){if("function"!=typeof n&&null!==n)throw new TypeError("Super expression must either be null or a function");t.prototype=Object.create(n&&n.prototype,{constructor:{value:t,writable:!0,configurable:!0}}),n&&r(t,n)}function r(t,n){return(r=Object.setPrototypeOf||function(t,n){return t.__proto__=n,t})(t,n)}function s(t,n){if(!(t instanceof n))throw new TypeError("Cannot call a class as a function")}var h=function t(n,i,e){s(this,t),this.left=n,this.operator=i,this.right=e},u=function(t){function i(){return s(this,i),n(this,e(i).apply(this,arguments))}return o(i,h),i}(),c=function t(n,i){s(this,t),this.operator=n,this.right=i},a=function t(n){var i=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";s(this,t),this.context=i,this.value=n},f=function t(n){s(this,t),this.name=n},l=function t(n,i){s(this,t),this.object=n,this.name=i},p=function t(n,i,e){s(this,t),this.object=n,this.name=i,this.value=e},y=function t(n){s(this,t),this.expression=n},m=function(t){function i(t){var o,r=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";return s(this,i),(o=n(this,e(i).call(this,t))).context=r,o}return o(i,y),i}(),b=function(t){function i(){return s(this,i),n(this,e(i).apply(this,arguments))}return o(i,y),i}(),g=function t(n,i){s(this,t),this.name=n,this.initializer=i},d=function t(n,i){s(this,t),this.name=n,this.value=i},v=function t(n){var i=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";s(this,t),this.context=i,this.statements=n},S=function t(n,i,e){s(this,t),this.condition=n,this.thenBranch=i,this.elseBranch=e},w=function t(n,i){var e=arguments.length>2&&void 0!==arguments[2]?arguments[2]:"while";s(this,t),this.context=e,this.condition=n,this.body=i},x=function t(n,i,e){s(this,t),this.callee=n,this.paren=i,this.arguments=e},O=function t(n,i){s(this,t),this.keyword=n,this.value=i},j=function t(n,i){s(this,t),this.name=n,this.methods=i},_=function t(n,i,e){s(this,t),this.name=n,this.params=i,this.bodyStatements=e};module.exports={Var:f,Binary:h,Unary:c,Block:v,Call:x,While:w,Class:j,Get:l,Set:p,Literal:a,Return:O,Logical:u,LoxFunction:_,Grouping:y,Condition:S,ExpressionStatement:m,PrintStatement:b,VarStatement:g,Assignment:d};
+function t(n){return(t="function"==typeof Symbol&&"symbol"==typeof Symbol.iterator?function(t){return typeof t}:function(t){return t&&"function"==typeof Symbol&&t.constructor===Symbol&&t!==Symbol.prototype?"symbol":typeof t})(n)}function n(n,e){return!e||"object"!==t(e)&&"function"!=typeof e?i(n):e}function i(t){if(void 0===t)throw new ReferenceError("this hasn't been initialised - super() hasn't been called");return t}function e(t){return(e=Object.setPrototypeOf?Object.getPrototypeOf:function(t){return t.__proto__||Object.getPrototypeOf(t)})(t)}function o(t,n){if("function"!=typeof n&&null!==n)throw new TypeError("Super expression must either be null or a function");t.prototype=Object.create(n&&n.prototype,{constructor:{value:t,writable:!0,configurable:!0}}),n&&r(t,n)}function r(t,n){return(r=Object.setPrototypeOf||function(t,n){return t.__proto__=n,t})(t,n)}function s(t,n){if(!(t instanceof n))throw new TypeError("Cannot call a class as a function")}var h=function t(n,i,e){s(this,t),this.left=n,this.operator=i,this.right=e},u=function(t){function i(){return s(this,i),n(this,e(i).apply(this,arguments))}return o(i,h),i}(),c=function t(n,i){s(this,t),this.operator=n,this.right=i},a=function t(n){var i=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";s(this,t),this.context=i,this.value=n},f=function t(n){s(this,t),this.name=n},l=function t(n,i){s(this,t),this.object=n,this.name=i},p=function t(n,i,e){s(this,t),this.object=n,this.name=i,this.value=e},y=function t(n){s(this,t),this.expression=n},m=function(t){function i(t){var o,r=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";return s(this,i),(o=n(this,e(i).call(this,t))).context=r,o}return o(i,y),i}(),b=function(t){function i(){return s(this,i),n(this,e(i).apply(this,arguments))}return o(i,y),i}(),d=function t(n,i){s(this,t),this.name=n,this.initializer=i},g=function t(n,i){s(this,t),this.name=n,this.value=i},v=function t(n){var i=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"regular";s(this,t),this.context=i,this.statements=n},S=function t(n,i,e){s(this,t),this.condition=n,this.thenBranch=i,this.elseBranch=e},w=function t(n,i){var e=arguments.length>2&&void 0!==arguments[2]?arguments[2]:"while";s(this,t),this.context=e,this.condition=n,this.body=i},x=function t(n,i,e){s(this,t),this.callee=n,this.paren=i,this.arguments=e},O=function t(n,i){s(this,t),this.keyword=n,this.value=i},j=function t(n){s(this,t),this.keyword=n},_=function t(n,i){s(this,t),this.name=n,this.methods=i},P=function t(n,i,e){s(this,t),this.name=n,this.params=i,this.bodyStatements=e};module.exports={Var:f,Binary:h,Unary:c,Block:v,Call:x,While:w,Class:_,Get:l,Set:p,Literal:a,Return:O,Logical:u,This:j,LoxFunction:P,Grouping:y,Condition:S,ExpressionStatement:m,PrintStatement:b,VarStatement:d,Assignment:g};
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N(t.operator,n,e),e>=n;case j.LESS:return N(t.operator,n,e),e<n;case j.LESS_EQUAL:return N(t.operator,n,e),e<=n;case j.EQUAL_EQUAL:return M(e,n);case j.BANG_EQUAL:return!M(e,n)}}}]),t}();module.exports=I;
 },{"./errors":"p8GN","./types":"39eF","./environment":"brut","./tokenizer":"u74b"}],"Focm":[function(require,module,exports) {
 var r=require("./tokenizer"),e=require("./parser"),n=require("./interpreter"),o=require("./environment"),t=function(o,t,a){var i=arguments.length>3&&void 0!==arguments[3]&&arguments[3],l=new r(o).scanTokens();i&&console.log(l);var u=new e(l).parse();i&&console.log(u);var v,s=new n(t,a),c=!0,p=!1,f=void 0;try{for(var w,y=u[Symbol.iterator]();!(c=(w=y.next()).done);c=!0){var d=w.value;v=s.interpret(d)}}catch(m){p=!0,f=m}finally{try{c||null==y.return||y.return()}finally{if(p)throw f}}return v},a=function(n){var o=new r(n).scanTokens();return new e(o).parse()};module.exports={run:t,parse:a,Environment:o};
 },{"./tokenizer":"u74b","./parser":"CUYV","./interpreter":"lmrS","./environment":"brut"}],"9/6S":[function(require,module,exports) {
@@ -17,5 +17,5 @@ function n(n){return r(n)||e(n)||t()}function t(){throw new TypeError("Invalid a
 },{"../types":"39eF"}],"KVVd":[function(require,module,exports) {
 
 },{}],"3hpa":[function(require,module,exports) {
-"use strict";var n=require("./index"),e=require("./errors"),r=require("./transpilers/lox"),t=require("fs"),a="",i=document.getElementById("code"),o=['// Interactive Iterative Fibonacci\nvar a = 0;\nvar b = 1;\nvar limit = prompt("Limit to find fib numbers", 10000);\n\nwhile (a < limit) {\n  print a;\n  var temp = a;\n  a = b;\n  b = temp + b;\n}\n','// Linked List via Closures\nfun Link(value, next) {\n  fun access(method) {\n    if (method == "value") return value;\n    if (method == "next") return next;\n    print "unknown method " + method;\n  }\n\n  return access;\n}\n\nfun traverse(n, fn) {\n  fn(n);\n  if (n("next") != nil) {\n    return traverse(n("next"), fn);\n  }\n  return n;\n}\n\nfun printValue (n) {\n  print n("value");\n}\n\nfun blank (n) {}\n\nfun printTail (n) {\n  var tail = traverse(n, blank);\n  print tail("value");\n}\n\nvar list = Link(1, Link(2, Link(3, nil)));\n\ntraverse(list, printValue);\nprintTail(list, printTail);','// Kitchen Sink\nfun hello (arg1, arg2) {\n  fun secondHi (helloer) {\n    print helloer + " says hello";\n  }\n  var str = arg1 + " says hello to " + arg2;\n  var maxAge = 18;\n  var age;\n  age = maxAge + 3;\n  if (age < 21) {\n    alert("Too young");\n    while(age < 21) {\n      age = age + 1;\n    }\n  } else {\n    print "come on in";\n  }\n  for (var i = 0; i < 18; i = i + 1) {\n    print i;\n  }\n  return age or maxAge;\n}\n\n\nprint "hello source: ";\nprint printFunctionBody(hello);\n\n// hello("boss", "man");','// Class Example\nclass Lox {\n  breakfast() {\n    print "Toast";\n  }\n}\n\nfun hello () {\n  print "Would you like some breakfast?";\n}\n\nprint Lox;\n\nprint hello;\nvar loxInstance = Lox();\n\nloxInstance.category = "Breakfast";\nprint loxInstance.category;\n\nprint Lox();\n\n// class Bagel {}\n// var bagel = Bagel();\n// print bagel; // Prints "Bagel instance".\n// print bagel.lox;'],l=o.map(function(n){return{name:n.split("\n")[0].replace(/[^\w\s]/gi,"").trim(),program:n}}),u=function(n){var r=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"";if(!n)return document.getElementById("error").style.maxHeight="0",null;console.error(n);var t=(0,e.formatLoxError)(n,r),a=t.oneLiner,i=t.preErrorSection,o=t.errorSection,l=t.postErrorSection,u=a;o&&(u+="<br />",u+="".concat(i,'<span class="error">').concat(o,"</span>").concat(l)),document.getElementById("error").style.maxHeight="150px",document.getElementById("errorText").innerHTML=u},c=document.getElementById("exampleProgram"),s=l.map(function(n,e){return'<option value="'.concat(e,'">').concat(n.name,"</option>")}).join("\n");c.innerHTML=s,c.onchange=function(n){var e=n.target.value;i.value=l[e].program};var m=0;if(window.location.hash){var p=+window.location.hash.replace(/[^\w\s]/gi,"").trim();p<c.length&&(m=p),c.value=m}i.value=l[m].program;var g=function(n){a+=n+"\n",console.log(n),document.getElementById("output").value=a},v=document.getElementById("run");v.onclick=function(){var e=i.value,t=new n.Environment;t.setBuiltin("alert",function(n,e){return alert(e[0])}),t.setBuiltin("printFunctionBody",function(n,e){var t=e[0];if(t&&!t.declaration)throw new Error("Argument is not a lox function");return(0,r.printLoxAST)(t.declaration)}),t.setBuiltin("confirm",function(n,e){return confirm(e[0])}),t.setBuiltin("prompt",function(n,e){return prompt(e[0],e.length>1?e[1]:null)}),a="";try{(0,n.run)(e,t,g),u(null)}catch(o){u(o,e)}};var f=document.getElementById("format");f.onclick=function(){try{i.value=(0,n.parse)(i.value).map(function(n){return(0,r.printLoxAST)(n)}).join("\n"),u(null)}catch(e){u(e,i.value)}};
+"use strict";var n=require("./index"),e=require("./errors"),r=require("./transpilers/lox"),t=require("fs"),a="",i=document.getElementById("code"),o=['// Interactive Iterative Fibonacci\nvar a = 0;\nvar b = 1;\nvar limit = prompt("Limit to find fib numbers", 10000);\n\nwhile (a < limit) {\n  print a;\n  var temp = a;\n  a = b;\n  b = temp + b;\n}\n','// Linked List via Closures\nfun Link(value, next) {\n  fun access(method) {\n    if (method == "value") return value;\n    if (method == "next") return next;\n    print "unknown method " + method;\n  }\n\n  return access;\n}\n\nfun traverse(n, fn) {\n  fn(n);\n  if (n("next") != nil) {\n    return traverse(n("next"), fn);\n  }\n  return n;\n}\n\nfun printValue (n) {\n  print n("value");\n}\n\nfun blank (n) {}\n\nfun printTail (n) {\n  var tail = traverse(n, blank);\n  print tail("value");\n}\n\nvar list = Link(1, Link(2, Link(3, nil)));\n\ntraverse(list, printValue);\nprintTail(list, printTail);','// Kitchen Sink\nfun hello (arg1, arg2) {\n  fun secondHi (helloer) {\n    print helloer + " says hello";\n  }\n  var str = arg1 + " says hello to " + arg2;\n  var maxAge = 18;\n  var age;\n  age = maxAge + 3;\n  if (age < 21) {\n    alert("Too young");\n    while(age < 21) {\n      age = age + 1;\n    }\n  } else {\n    print "come on in";\n  }\n  for (var i = 0; i < 18; i = i + 1) {\n    print i;\n  }\n  return age or maxAge;\n}\n\n\nprint "hello source: ";\nprint printFunctionBody(hello);\n\n// hello("boss", "man");','// Class Example\nclass Lox {\n  breakfast() {\n    print "Toast";\n    this.hello = "toast";\n    return this.hello;\n  }\n}\n\nfun hello () {\n  print "Would you like some breakfast?";\n}\n\nprint Lox;\n\nprint hello;\nvar loxInstance = Lox();\n\nloxInstance.category = "Breakfast";\nprint loxInstance.category;\nprint loxInstance.breakfast();\n\nprint Lox();\n\n// class Bagel {}\n// var bagel = Bagel();\n// print bagel; // Prints "Bagel instance".\n// print bagel.lox;'],l=o.map(function(n){return{name:n.split("\n")[0].replace(/[^\w\s]/gi,"").trim(),program:n}}),u=function(n){var r=arguments.length>1&&void 0!==arguments[1]?arguments[1]:"";if(!n)return document.getElementById("error").style.maxHeight="0",null;console.error(n);var t=(0,e.formatLoxError)(n,r),a=t.oneLiner,i=t.preErrorSection,o=t.errorSection,l=t.postErrorSection,u=a;o&&(u+="<br />",u+="".concat(i,'<span class="error">').concat(o,"</span>").concat(l)),document.getElementById("error").style.maxHeight="150px",document.getElementById("errorText").innerHTML=u},c=document.getElementById("exampleProgram"),s=l.map(function(n,e){return'<option value="'.concat(e,'">').concat(n.name,"</option>")}).join("\n");c.innerHTML=s,c.onchange=function(n){var e=n.target.value;i.value=l[e].program};var m=0;if(window.location.hash){var p=+window.location.hash.replace(/[^\w\s]/gi,"").trim();p<c.length&&(m=p),c.value=m}i.value=l[m].program;var g=function(n){a+=n+"\n",console.log(n),document.getElementById("output").value=a},v=document.getElementById("run");v.onclick=function(){var e=i.value,t=new n.Environment;t.setBuiltin("alert",function(n,e){return alert(e[0])}),t.setBuiltin("printFunctionBody",function(n,e){var t=e[0];if(t&&!t.declaration)throw new Error("Argument is not a lox function");return(0,r.printLoxAST)(t.declaration)}),t.setBuiltin("confirm",function(n,e){return confirm(e[0])}),t.setBuiltin("prompt",function(n,e){return prompt(e[0],e.length>1?e[1]:null)}),a="";try{(0,n.run)(e,t,g),u(null)}catch(o){u(o,e)}};var f=document.getElementById("format");f.onclick=function(){try{i.value=(0,n.parse)(i.value).map(function(n){return(0,r.printLoxAST)(n)}).join("\n"),u(null)}catch(e){u(e,i.value)}};
 },{"./index":"Focm","./errors":"p8GN","./transpilers/lox":"9/6S","fs":"KVVd"}]},{},["3hpa"], null)
\ No newline at end of file
diff --git a/errors.js b/errors.js
index e018edf..45eeb7c 100644
--- a/errors.js
+++ b/errors.js
@@ -12,6 +12,16 @@ class LoxError {
   }
 }
 
+class RuntimeError extends LoxError {
+  constructor(msg, token) {
+    super(
+      `${nullable(token.lexeme && `at "${token.lexeme}": `)}${msg}`,
+      token.startCoordinates,
+      token.endCoordinates
+    )
+  }
+}
+
 class ReturnError {
   constructor(val) {
     this.value = val
@@ -33,12 +43,7 @@ const parseError = (msg, token) => {
   }
 }
 
-const runtimeError = (msg, token) =>
-  new LoxError(
-    `${nullable(token.lexeme && `at "${token.lexeme}": `)}${msg}`,
-    token.startCoordinates,
-    token.endCoordinates
-  )
+const runtimeError = (msg, token) => new RuntimeError(msg, token)
 
 const formatLoxError = (e, code) => {
   if (e instanceof LoxError) {
@@ -55,8 +60,9 @@ const formatLoxError = (e, code) => {
     const postErrorSection = code.substring(e.endCoordinates.index, postErrorStart)
 
     // Print Critical Code
+    const errorType = e instanceof RuntimeError ? 'Runtime Error' : 'Parse Error'
     return {
-      oneLiner: `Parse Error: ${e.toString()} at ${e.endCoordinates.line}:${e.endCoordinates.col +
+      oneLiner: `${errorType}: ${e.toString()} at ${e.endCoordinates.line}:${e.endCoordinates.col +
         1}`,
       preErrorSection,
       errorSection,
diff --git a/examples/classExample.lox b/examples/classExample.lox
index 23ead97..74b74e6 100644
--- a/examples/classExample.lox
+++ b/examples/classExample.lox
@@ -2,6 +2,8 @@
 class Lox {
   breakfast() {
     print "Toast";
+    this.hello = "toast";
+    return this.hello;
   }
 }
 
@@ -16,6 +18,7 @@ var loxInstance = Lox();
 
 loxInstance.category = "Breakfast";
 print loxInstance.category;
+print loxInstance.breakfast();
 
 print Lox();
 
diff --git a/examples/linkedList.lox b/examples/linkedList.lox
new file mode 100644
index 0000000..456dd12
--- /dev/null
+++ b/examples/linkedList.lox
@@ -0,0 +1,42 @@
+// Linked List via Classes
+class Link {}
+
+fun newLink (value, next) {
+  var link = Link();
+  link.value = value;
+  link.next = next;
+  link.append
+  return link;
+}
+
+var ll = newLink(1, newLink(2, newLink(3, nil)));
+
+fun traverse(n, fn) {
+  fn(n);
+  if (n.next != nil) {
+    return traverse(n.next, fn);
+  }
+  return n;
+}
+
+fun printList(list) {
+  fun printNode (n) {
+    print n.value;
+  }
+  traverse(list, printNode);
+}
+
+fun append(list, newNode) {
+  fun walk (n) {}
+  var end = traverse(list, walk);
+  end.next = newNode;
+  return end;
+}
+
+print "list:";
+printList(ll);
+
+append(ll, newLink(40, nil));
+
+print "list:";
+printList(ll);
\ No newline at end of file
diff --git a/interpreter.js b/interpreter.js
index c5579d0..5ee6acb 100644
--- a/interpreter.js
+++ b/interpreter.js
@@ -9,6 +9,7 @@ const {
   Get,
   Set,
   Var,
+  This,
   Grouping,
   Return,
   While,
@@ -57,15 +58,22 @@ class LoxCallable {
     return null
   }
 
+  bind(instance) {
+    const env = new Environment(this.closure)
+    env.set({ lexeme: 'this' }, instance)
+    return new LoxCallable(this.declaration, env)
+  }
+
   toString() {
     return `<${this.declaration.name.lexeme}()>`
   }
 }
 
 class LoxClass extends LoxCallable {
-  constructor(name) {
+  constructor(name, methods) {
     super()
     this.name = name
+    this.methods = methods
   }
 
   call() {
@@ -85,11 +93,11 @@ class LoxInstance {
 
   get(token) {
     const name = token.lexeme
-    if (this.fields.has(name)) {
-      return this.fields.get(name)
-    }
+    if (this.fields.has(name)) return this.fields.get(name)
 
-    throw runtimeError(`Undefined property ${name}`, token)
+    if (this.klass.methods.has(name)) return this.klass.methods.get(name).bind(this)
+
+    throw runtimeError(`Undefined property "${name}"`, token)
     // return null
   }
 
@@ -126,6 +134,7 @@ class Interpreter {
     else if (expr instanceof Class) return this.visitClass(expr)
     else if (expr instanceof Get) return this.visitGet(expr)
     else if (expr instanceof Set) return this.visitSet(expr)
+    else if (expr instanceof This) return this.visitThis(expr)
     else if (expr instanceof Logical) return this.visitLogical(expr)
     else if (expr instanceof Call) return this.visitCall(expr)
     else if (expr instanceof While) return this.visitWhile(expr)
@@ -200,7 +209,12 @@ class Interpreter {
   visitClass(stmt) {
     // We set the name before initializing it so classes can self-reference
     this.environment.set(stmt.name, null)
-    const klass = new LoxClass(stmt.name.lexeme)
+    const methods = new Map()
+    for (let method of stmt.methods) {
+      const fun = new LoxCallable(method, this.environment)
+      methods.set(method.name.lexeme, fun)
+    }
+    const klass = new LoxClass(stmt.name.lexeme, methods)
     this.environment.assign(stmt.name, klass)
     return null
   }
@@ -225,6 +239,10 @@ class Interpreter {
     return object.set(expr.name, val)
   }
 
+  visitThis(expr) {
+    return this.environment.get({ name: expr.keyword })
+  }
+
   visitBlock(expr) {
     this.interpretBlock(expr.statements, new Environment(this.environment))
     return null
diff --git a/loxfmt.js b/loxfmt.js
index 3a698a5..da0bc62 100755
--- a/loxfmt.js
+++ b/loxfmt.js
@@ -80,4 +80,4 @@ const main = argv => {
   }
 }
 
-return main(process.argv)
+main(process.argv)
diff --git a/parser.js b/parser.js
index 0fda4be..ca38f29 100644
--- a/parser.js
+++ b/parser.js
@@ -9,6 +9,7 @@ const {
   Class,
   Get,
   Set,
+  This,
   Grouping,
   Return,
   LoxFunction,
@@ -262,6 +263,7 @@ class Parser {
   call() {
     let expr = this.primary()
     while (true) {
+      //eslint-disable-line
       if (this.match(token.LEFT_PAREN)) {
         expr = this.finishCall(expr)
       } else if (this.match(token.DOT)) {
@@ -291,6 +293,7 @@ class Parser {
     if (this.match(token.TRUE)) return new Literal(true)
     if (this.match(token.NIL)) return new Literal(null)
     if (this.match(token.NUMBER, token.STRING)) return new Literal(this.previous().literal)
+    if (this.match(token.THIS)) return new This(this.previous())
     if (this.match(token.IDENTIFIER)) return new Var(this.previous())
 
     if (this.match(token.LEFT_PAREN)) {
diff --git a/types.js b/types.js
index dba5bad..730aaf7 100644
--- a/types.js
+++ b/types.js
@@ -109,6 +109,12 @@ class Return {
   }
 }
 
+class This {
+  constructor(keyword) {
+    this.keyword = keyword
+  }
+}
+
 class Class {
   constructor(name, methods) {
     this.name = name
@@ -137,6 +143,7 @@ module.exports = {
   Literal,
   Return,
   Logical,
+  This,
   LoxFunction,
   Grouping,
   Condition,