code 128 barcode generator asp.net I THE F# LIBRARIES in Font

Drawer DataMatrix in Font I THE F# LIBRARIES

The basic placeholders in a Printf module function are %b for a Boolean; %s for a string; %d or %i for an integer; %u for an unsigned integer; and %x, %X, or %o for an integer formatted as a hexadecimal. It is also possible to specify the number of decimal places that are displayed in numeric types. The following example demonstrates this: #light let pi = System.Math.PI Printf.printf Printf.printf Printf.printf Printf.printf "%f\r\n" pi "%1.1f\r\n" pi "%2.2f\r\n" pi "%2.8f\r\n" pi

The results of this code are as follows: 3.141593 3.1 3.14 3.14159265 The Printf module also contains a number of other functions that allow a string to be formatted in the same ways as printf itself but allow the result to be written to a different destination. The following example shows some of the different versions available: #light // write to a string let s = Printf.sprintf "Hello %s\r\n" "string" print_string s // prints the string to the given channel Printf.fprintf stdout "Hello %s\r\n" "channel" // prints the string to a .NET TextWriter Printf.twprintf System.Console.Out "Hello %s\r\n" "TextWriter" // create a string that will be placed // in an exception message Printf.failwithf "Hello %s" "exception" The results of this code are as follows: Hello string Hello channel Hello TextWriter Microsoft.FSharp.FailureException: Hello exception at Microsoft.FSharp.Text.Printf.failwithf@60.Invoke(String s) at Microsoft.FSharp.Text.PrintfImpl.Make@188.Invoke(A inp)) at <StartupCode>.FSI_0003._main() stopped due to error

You can think of an event in F# as a collection of functions that can be triggered by a call to a function. The idea is that functions will register themselves with the event, the collection of functions, to await notification that the event has happened. The trigger function is then used to give notice that the event has happened, causing all the functions that have added themselves to the event to be executed. I will cover the following features of the IEvent module: Creating and handling events: The basics of creating and handling events using the create and add functions The filter function: A function to filter the data coming into events The partition function: A function that splits the data coming into events into two The map function: A function that maps the data before it reaches the event handler

The first example looks at a simple event being created using the IEvent module s create function. This function returns a tuple containing the trigger function as its first item and the event itself as its second item. Often you need to add type annotations to say what type of event you want, that is, what type of parameter your event s handler functions should take. After this, you use the event s Add function to add a handler method, and finally you trigger the event using the trigger function: #light let trigger, event = IEvent.create<string>() event.Add(fun x -> printfn "%s" x) trigger "hello" The result of this code is as follows: hello In addition to this basic event functionality, the F# IEvent module provides a number of functions that allow you to filter and partition events to give fine-grained control over which data is passed to which event handler.

The following example demonstrates how you can use the IEvent module s filter function so that data being passed to the event is filtered before it reaches the event handlers. In this example, you filter the data so that only strings beginning with H are sent to the event handler:

#light let trigger, event = IEvent.create<string>() let newEvent = event |> IEvent.filter (fun x -> x.StartsWith("H")) newEvent.Add(fun x -> printfn "new event: %s" x) trigger trigger trigger trigger trigger "Harry" "Jane" "Hillary" "John" "Henry"

The results of this code, when compiled and executed, are as follows: new event: Harry new event: Hillary new event: Henry