ASP.NET Web PDF Document Viewer/Editor Control Library

To set a breakpoint on the desired lines, click in the gutter on the left side of the desired line of code. Each time you click the line, the line will cycle through one of three breakpoint settings: none, hard breakpoint, and future breakpoint. A hard breakpoint is denoted by a red B, and a future breakpoint is denoted by an orange F. Lines of code that exist outside the body of a function will cycle only through no breakpoints and future breakpoints; code within a function body will cycle through no breakpoints, hard breakpoints, and future breakpoints. With breakpoints now set, you can try initiating an action that will cause a breakpoint to be encountered. The breakpoints.html page has a single button. Clicking the button calls the doFoo method, which does nothing more than create a couple of variables. When the doFoo button is clicked in the browser window, the doFoo method is called, and the breakpoint on line 15 is encountered. When this breakpoint is encountered, the execution of the JavaScript suspends until further notice. The Venkman window opens in front of the browser window, and the breakpoint is now highlighted, as shown in Figure 7-14.

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let _ = getShorty() // -- or -ignore(getShorty()) // -- or -getShorty() |> ignore First you define the function getShorty, which returns a string. Now imagine, for whatever reason, you want to call this function and ignore its result. The next two lines demonstrate different ways to do this. First, you can use a let expression with an underscore (_) character in place of the identifier. The underscore tells the compiler this is a value in which you aren t interested. Second, this is such a common thing to do that it has been wrapped into a function, ignore, which is available in the F# base libraries and is demonstrated on the third line. The final line shows an alternative way of calling ignore using the pass-forward operator to pass the result of getShorty() to the ignore function. I explain the pass-forward operator in the The |> Operator section.

In 3 I talked about how you could bind identifiers to values using the keyword let and noted how under some circumstances you could redefine and rebound, but not modify, these identifiers. If you want to define an identifier whose value can change over time, you can do this using the mutable keyword. A special operator, the left ASCII arrow (or just left arrow), is composed of a less-than sign and a dash (<-) and is used to update these identifiers. An update operation using the left arrow has type unit, so you can chain these operations together as discussed in the previous section. The next example demonstrates defining a mutable identifier of type string and then changing the changing the value it holds: #light let mutable phrase = "How can I be sure, " print_endline phrase phrase <- "In a world that's constantly changing" print_endline phrase The results are as follows: How can I be sure, In a world that's constantly changing At first glance this doesn t look too different from redefining an identifier, but it has a couple of key differences. When you use the left arrow to update a mutable identifier, you can change its value but not its type when you redefine an identifier, you can do both. A compile error is produced if you try to change the type; the next example demonstrates this:

Figure 1-14. Sound level value versus sound pressure level Looking back at Figure 1-10, you can see that human vision has peak sensitivity to green light and drops off to zero toward both blue and red. Human sound sensitivity also has a peak. It s around a few kHz and drops off to zero toward both 20Hz and 20kHz. The Sound Sensor can be put into a dBA mode, in which the sound reading more closely matches that of the human ear. A rough idea of the frequency response of the Sound Sensor in the two modes is shown in Figure 1-15.