refactored Casper.evaluate() in order to accept arguments!

So basically now you can do:

``` js
casper.evaluate(function(username, password) {
    document.querySelector('#username').value = username;
    document.querySelector('#password').value = password;
    document.querySelector('#submit').click();
}, {
    username: 'Bazoonga',
    password: 'baz00nga'
})
```

@@ -120,11 +120,9 @@
          * @return string       Base64 encoded result
          */
         base64encode: function(url) {
-            return this.evaluate(function() {
-                return __utils__.getBase64(__casper_params__.url);
-            }, {
-                url: url
-            });
+            return this.evaluate(function(url) {
+                return __utils__.getBase64(url);
+            }, { url: url });
         },
 
         /**
@@ -168,9 +166,9 @@
          * @return Casper
          */
         captureSelector: function(targetFile, selector) {
-            return this.capture(targetFile, this.evaluate(function() {
+            return this.capture(targetFile, this.evaluate(function(selector) {
                 try {
-                    var clipRect = document.querySelector(__casper_params__.selector).getBoundingClientRect();
+                    var clipRect = document.querySelector(selector).getBoundingClientRect();
                     return {
                         top:    clipRect.top,
                         left:   clipRect.left,
@@ -178,11 +176,9 @@
                         height: clipRect.height
                     };
                 } catch (e) {
-                    __utils__.log("Unable to fetch bounds for element " + __casper_params__.selector, "warning");
+                    __utils__.log("Unable to fetch bounds for element " + selector, "warning");
                 }
-            }, {
-                selector: selector
-            }));
+            }, { selector: selector }));
         },
 
         /**
@@ -224,8 +220,8 @@
         click: function(selector, fallbackToHref) {
             fallbackToHref = isType(fallbackToHref, "undefined") ? true : !!fallbackToHref;
             this.log("click on selector: " + selector, "debug");
-            return this.evaluate(function() {
-                return __utils__.click(__casper_params__.selector, __casper_params__.fallbackToHref);
+            return this.evaluate(function(selector, fallbackToHref) {
+                return __utils__.click(selector, fallbackToHref);
             }, {
                 selector:       selector,
                 fallbackToHref: fallbackToHref
@@ -323,24 +319,12 @@
 
         /**
          * Evaluates an expression in the page context, a bit like what
-         * WebPage#evaluate does, but can also replace values by their
-         * placeholer names:
+         * WebPage#evaluate does, but the passed function can also accept
+         * parameters if a context Object is also passed:
          *
-         *     casper.evaluate(function() {
-         *         document.querySelector('#username').value = '%username%';
-         *         document.querySelector('#password').value = '%password%';
-         *         document.querySelector('#submit').click();
-         *     }, {
-         *         username: 'Bazoonga',
-         *         password: 'baz00nga'
-         *     })
-         *
-         * As an alternative, CasperJS injects a `__casper_params__` Object
-         * instance containing all the parameters you passed:
-         *
-         *     casper.evaluate(function() {
-         *         document.querySelector('#username').value = __casper_params__.username;
-         *         document.querySelector('#password').value = __casper_params__.password;
+         *     casper.evaluate(function(username, password) {
+         *         document.querySelector('#username').value = username;
+         *         document.querySelector('#password').value = password;
          *         document.querySelector('#submit').click();
          *     }, {
          *         username: 'Bazoonga',
@@ -351,25 +335,15 @@
          * arguments to the function.
          * TODO: don't forget to keep this backward compatible.
          *
-         * @param  function  fn            The function to be evaluated within current page DOM
-         * @param  object    replacements  Parameters to pass to the remote environment
+         * @param  Function  fn       The function to be evaluated within current page DOM
+         * @param  Object    context  Object containing the parameters to inject into the function
          * @return mixed
          * @see    WebPage#evaluate
          */
-        evaluate: function(fn, replacements) {
-            replacements = isType(replacements, "object") ? replacements : {};
-            this.page.evaluate(replaceFunctionPlaceholders(function() {
-                window.__casper_params__ = {};
-                try {
-                    var jsonString = unescape(decodeURIComponent('%replacements%'));
-                    window.__casper_params__ = JSON.parse(jsonString);
-                } catch (e) {
-                    __utils__.log("Unable to replace parameters: " + e, "error");
-                }
-            }, {
-                replacements: encodeURIComponent(escape(JSON.stringify(replacements).replace("'", "\'")))
-            }));
-            return this.page.evaluate(replaceFunctionPlaceholders(fn, replacements));
+        evaluate: function(fn, context) {
+            context = isType(context, "object") ? context : {};
+            var newFn = new phantom.Casper.FunctionArgsInjector(fn, context).process();
+            return this.page.evaluate(newFn);
         },
 
         /**
@@ -395,11 +369,9 @@
          * @return Boolean
          */
         exists: function(selector) {
-            return this.evaluate(function() {
-                return __utils__.exists(__casper_params__.selector);
-            }, {
-                selector: selector
-            });
+            return this.evaluate(function(selector) {
+                return __utils__.exists(selector);
+            }, { selector: selector });
         },
 
         /**
@@ -411,11 +383,9 @@
          * @return Boolean
          */
         visible: function(selector) {
-            return this.evaluate(function() {
-                return __utils__.visible(__casper_params__.selector);
-            }, {
-                selector: selector
-            });
+            return this.evaluate(function(selector) {
+                return __utils__.visible(selector);
+            }, { selector: selector });
         },
 
         /**
@@ -437,11 +407,9 @@
          * @return String
          */
         fetchText: function(selector) {
-            return this.evaluate(function() {
-                return __utils__.fetchText(__casper_params__.selector);
-            }, {
-                selector: selector
-            });
+            return this.evaluate(function(selector) {
+                return __utils__.fetchText(selector);
+            }, { selector: selector });
         },
 
         /**
@@ -459,8 +427,8 @@
             if (!isType(vals, "object")) {
                 throw "form values must be provided as an object";
             }
-            var fillResults = this.evaluate(function() {
-               return __utils__.fill(__casper_params__.selector, __casper_params__.values);
+            var fillResults = this.evaluate(function(selector, values) {
+               return __utils__.fill(selector, values);
             }, {
                 selector: selector,
                 values:   vals
@@ -489,15 +457,13 @@
             }
             // Form submission?
             if (submit) {
-                this.evaluate(function() {
-                    var form = document.querySelector(__casper_params__.selector);
+                this.evaluate(function(selector) {
+                    var form = document.querySelector(selector);
                     var method = form.getAttribute('method').toUpperCase() || "GET";
                     var action = form.getAttribute('action') || "unknown";
                     __utils__.log('submitting form to ' + action + ', HTTP ' + method, 'info');
                     form.submit();
-                }, {
-                    selector: selector
-                });
+                }, { selector: selector });
             }
         },
 
@@ -532,8 +498,7 @@
          * @return mixed
          */
         getGlobal: function(name) {
-            var result = this.evaluate(function() {
-                var name = window.__casper_params__.name;
+            var result = this.evaluate(function(name) {
                 var result = {};
                 try {
                     result.value = JSON.stringify(window[name]);
@@ -787,13 +752,13 @@
          * current retrieved page DOM.
          *
          * @param  function  fn       The function to be evaluated within current page DOM
-         * @param  object    replacements  Optional replacements to performs, eg. for '%foo%' => {foo: 'bar'}
+         * @param  object    context  Optional function parameters context
          * @return Casper
          * @see    Casper#evaluate
          */
-        thenEvaluate: function(fn, replacements) {
+        thenEvaluate: function(fn, context) {
             return this.then(function(self) {
-                self.evaluate(fn, replacements);
+                self.evaluate(fn, context);
             });
         },
 
@@ -820,13 +785,13 @@
          *
          * @param  String    location  The url to open
          * @param  function  fn        The function to be evaluated within current page DOM
-         * @param  object    replacements  Optional replacements to performs, eg. for '%foo%' => {foo: 'bar'}
+         * @param  object    context   Optional function parameters context
          * @return Casper
          * @see    Casper#evaluate
          * @see    Casper#open
          */
-        thenOpenAndEvaluate: function(location, fn, replacements) {
-            return this.thenOpen(location).thenEvaluate(fn, replacements);
+        thenOpenAndEvaluate: function(location, fn, context) {
+            return this.thenOpen(location).thenEvaluate(fn, context);
         },
 
         /**
@@ -1681,6 +1646,51 @@
     };
 
     /**
+     * Function argument injector.
+     *
+     */
+    phantom.Casper.FunctionArgsInjector = function(fn, values) {
+        this.fn = fn;
+        this.values = typeof values === "object" ? values : {};
+
+        this.extract = function(fn) {
+            var match = /^function\s?(\w+)?\s?\((.*)\)\s?\{([\s\S]*)\}/i.exec(fn.toString().trim());
+            if (match && match.length > 1) {
+                var args = match[2].split(',').map(function(arg) {
+                    return arg.replace(new RegExp(/\/\*+.*\*\//ig), "").trim();
+                }).filter(function(arg) {
+                    return arg;
+                }) || [];
+                return {
+                    name: match[1] ? match[1].trim() : null,
+                    args: args,
+                    body: match[3] ? match[3].trim() : ''
+                };
+            }
+        };
+
+        this.process = function() {
+            var fnObj = this.extract(this.fn);
+            var inject = this.getArgsInjectionString(fnObj.args, this.values);
+            return 'function ' + (fnObj.name || '') + '(){' + inject + fnObj.body + '}';
+        };
+
+        this.getArgsInjectionString = function(args, values) {
+            values = typeof values === "object" ? values : {};
+            var jsonValues = escape(encodeURIComponent(JSON.stringify(values)));
+            var inject = [
+                'var __casper_params__ = JSON.parse(decodeURIComponent(unescape(\'' + jsonValues + '\')));'
+            ];
+            args.forEach(function(arg) {
+                if (arg in values) {
+                    inject.push('var ' + arg + '=__casper_params__["' + arg + '"];');
+                }
+            });
+            return inject.join('\n') + '\n';
+        };
+    };
+
+    /**
      * JUnit XML (xUnit) exporter for test results.
      *
      */
@@ -1817,7 +1827,7 @@
                     }
                 }
             }
-            // Client utils injection
+            // Client-side utils injection
             var injected = page.evaluate(replaceFunctionPlaceholders(function() {
                 eval("var ClientUtils = " + decodeURIComponent("%utils%"));
                 __utils__ = new ClientUtils();

@@ -78,7 +78,7 @@ fs.remove(testFile);
 
 // Casper#evaluate()
 casper.then(function(self) {
-    self.test.comment('evaluating');
+    self.test.comment('Casper.evaluate()');
     var params = {
         "boolean true":  true,
         "boolean false": false,
@@ -92,7 +92,7 @@ casper.then(function(self) {
         return __casper_params__;
     }, params);
     self.test.assertType(casperParams, "object", 'Casper.evaluate() exposes parameters in a dedicated object');
-    self.test.assertEquals(Object.keys(casperParams).length, 7, 'Casper.evaluate() exposes parameters object has the correct length');
+    self.test.assertEquals(Object.keys(casperParams).length, 7, 'Casper.evaluate() object containing parameters has the correct length');
     for (var param in casperParams) {
         self.test.assertEquals(JSON.stringify(casperParams[param]), JSON.stringify(params[param]), 'Casper.evaluate() can pass a ' + param);
         self.test.assertEquals(typeof casperParams[param], typeof params[param], 'Casper.evaluate() preserves the ' + param + ' type');