.NET/Java PDF, Tiff, Barcode SDK Library

A powerful aspect of XMLHttpRequest Debugging is that it allows you to create a new Ajax request based on a previous request. Click the edit&replay link to open the window, as shown in Figure 7-3. Here you ll see the data listed from the request from which you started, but now all the fields are editable. You can change the request method, update the URL, add some request headers, and even add a string of data or XML that is sent along as part of the request body. Click the send link to send the newly created request. This particular tool is powerful when you want to experiment with different request types and data without having to manually update the script, deploy it to the Web server, and repeat the test. The Greasemonkey extension for the Firefox browser, combined with the XMLHttpRequest Debugging user script, is a powerful tool for Ajax debugging and development. It can help trace exactly what is happening in the browser, and if something goes wrong, you ll have the information you need to quickly debug Figure 7-3. A request from the previous the problem. It can help isolate whether example was changed to use the POST a problem exists in the browser-side client method, and the query string was moved script or in the server-side code that servfrom the URL to the request body. ices the request.

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let printVolumes x = printfn "Volume in liters = %f, in us pints = %f, in imperial pints = %f" (convertVolumeToLiter x) (convertVolumeUsPint x) (convertVolumeImperialPint x) printVolumes vol1 printVolumes vol2 printVolumes vol3 The results of these examples, when compiled and executed, are as follows: Volume in liters = 2.500000, in us pints = 5.282500, in imperial pints = 4.400000 Volume in liters = 1.182500, in us pints = 2.500000, in imperial pints = 2.082500 Volume in liters = 1.420000, in us pints = 3.002500, in imperial pints = 2.500000 Both union and record types can be parameterized. Parameterizing a type means leaving one or more of the types within the type being defined to be determined later by the consumer of the types. This is a similar concept to the variable types discussed earlier in this chapter. When defining types, you must be a little bit more explicit about which types are variable. F# supports two syntaxes for type parameterization. In the first, you place the type being parameterized between the keyword type and the name of the type, as follows: #light type 'a BinaryTree = | BinaryNode of 'a BinaryTree * 'a BinaryTree | BinaryValue of 'a let tree1 = BinaryNode( BinaryNode ( BinaryValue 1, BinaryValue 2), BinaryNode ( BinaryValue 3, BinaryValue 4) )

Figure 13-15. Keypad Input built with the Mindsensors Prototype Board You could build the Keypad Input using the construction methods we have already discussed, but Mindsensors sells a PCF8574 prototype board that is perfect for the job. (More information about this board can be found in Appendix A.) All you need is to combine it with a 16-button matrix keypad such as the Grayhill 96BB2-056-R (Digi-Key #GH5011-ND). That is a 4-by-4 style keypad in which the buttons are connected in a row-and-column format (see Figure 13-16). The columns are connected to the top 4 bits, while the rows are connected to the bottom 4 bits of the PCF8574.

Sooner or later during your Ajax development you re going to have some bugs in JavaScript code. Some of the bugs will be easy to find because they re syntactic in nature. Others will be more difficult to find because they re subtle errors in business logic. That s when a debugger tool comes in handy so you can step through the code, line by line, and verify that the scripts are flowing as expected and that the variables have the correct values. You can use three tools to help you debug JavaScript: Firefox JavaScript Console: Firefox JavaScript Console records all errors and warnings that occur within JavaScript. It s easy to use, and you can quickly diagnose most errors using the JavaScript Console, without resorting to a full-fledged debugging environment. Microsoft Script Debugger: This tool integrates with Internet Explorer and provides basic debugging facilities such as the ability to set breakpoints and the ability to inspect and modify the values of variables during runtime. It s a relatively primitive tool, although it may fit nicely in situations where many Internet Explorer specific behaviors are used or where the debugging errors occur only in Internet Explorer.

In the second syntax, you place the types being parameterized in angle brackets after the type name, as follows: #light type Tree<'a> = | Node of Tree<'a> list | Value of 'a let tree2 = Node( [ Node( [Value "one"; Value "two"] ) ; Node( [Value "three"; Value "four"] ) ]