Creating ASP.NET Classes with APLScript

As mentioned previously, the original purpose of APLScript was to provide the ability to write ASP.NET Web Pages and Web Services in Dyalog. Both these applications are based upon script files.

Web Page Layout

An ASP.NET Web Page typically consists of a mixture of HTML and code written in a scripting language. The script code is separated from the HTML by being embedded within tags and normally appears in the

section of the page. Only one block of script is allowed in a page. The script block normally consists of a collection of functions, which are invoked by some event on the page, or on an element of the page.

APLScript code starts with a statement:

<script language="Dyalog" runat=server>

and finishes with:

</script>

Typically, the APLScript code consists of callback functions that are attached to server-side events on the page.

For further information, see The web.config file.

Web Service Layout

The first line in a Web Service script must be a declaration statement such as:

<%@ WebService Language="Dyalog" Class="ServiceName" %>

where ServiceName is an arbitrary name that identifies your Web Service.

The next statement must be a :Class statement that declares the name of the Web Service and its Base Class from which it inherits. The base class will normally be System.Web.Services.WebService. For example:

:Class ServiceName: System.Web.Services.WebService

The last line in the script must be:

:EndClass

Although it may appear awkward to have to specify the name of your Web Service twice, this is necessary because the two statements are being processed quite separately by different software components. The first statement is processed by ASP.NET. When it sees Language="Dyalog", it then calls the Dyalog APLScript compiler, passing it the remainder of the script file. The :Class statement tells the APLScript compiler the name of the Web Service and its base class. :Class and :EndClass statements are private directives to the APLScript compiler and are not relevant to ASP.NET.

How APLScript is processed by ASP.NET

Like any other Web Page or Web Service, an APLScript file is processed by ASP.NET.

The first time ASP.NET processes a script file, it first performs a compilation process whose output is a .NET assembly. ASP.NET then calls the code in this assembly to generate the HTML (for a Web Page) or to run a method (for a Web Service).

ASP.NET associates the compiled assembly with the script file, and only recompiles it if/when it has changed.

ASP.NET does not itself compile a script; it delegates this task to a specialised compiler that is associated with the language declared in the script. This association is made either in the application's web.config file or in the global machine.config file. Dyalog Installs a default web.config file which includes these settings in the samples\asp.net folder.

The APLScript compiler is itself written in Dyalog.

Although the compilation process takes some time, it is typically only performed once, so the performance of an APLScript Web Service or Web Page is not compromised. Once it has been compiled, ASP.NET redirects all subsequent requests for an APLScript to its compiled assembly.

Please note that the use of the word compile in this process does not imply that your APL code is actually compiled into Microsoft Intermediate Language (MSIL). Although the process does in fact generate some MSIL, your APL code will still be interpreted by the Dyalog DLL engine at run-time. The word compile is used only to be consistent with the messages displayed by ASP.NET when it first processes the script.