MildServer: Debugging

Once the MildServer is running on your machine (see MildServer/GettingStarted), you should be able to direct your browser to http://localhost:8080 and see the front page:

The front page is implemented by the file called index.dyalog in the Demo folder, which has the following content:

:Class Index : MildPage

    :Include #.HTMLInput

    ∇ Render req;html;links;hdr
      :Access Public
     
      hdr←'h2'Enclose'Welcome to MildServer'
      html←#.Files.GetText req.Server.Root,'welcome.txt'
      req.Return hdr,'p' Enclose html
    ∇

:EndClass

The first line declares that this is a Class called Index, which derives from a base class called MildPage (which you don't need to know about, but in case you are curious, it happens to be implemented by the file Core\MildPage.dyalog). As soon as this page has been viewed for the first time, the class Index will have been defined in the root of the server workspace. There is also a utility function in the root of the server workspace which you can use to load pages, the page could have been loaded into the workspace by typing (Load 'index').

The example is discussed in more detail on the next page: Samples: The index page.

To debug a page as it runs, the easiest thing to do is to insert an intentional error into the code. When you next refer to the page using a browser, the code will crash on your error and the Dyalog debugger will open up. You can now trace through the code and change it. Each time you exit from the function editor, you will be asked whether you want to overwrite the source file, or only make the change in the active workspace.

IMPORTANT: When resuming after editing a function, always use the GREEN button in the tracer ("Restart all threads"). By default, APL will halt all threads on an error - and this includes the main listener thread. If you don't restart all threads, the server will stop responding to requests. If the server stops responding, try the menu item Threads|Resume all threads to see whether the main thread is paused.

Using External Editors

If you have a Unicode keyboard or the Dyalog IME installed, you can also edit the pages using Notepad or other text editors. The MildServer will check the timestamp of the source file on each request and reload the source if it has changed.

Beware: If you alternate between editing the class in the worspace and using an external editor, note that some simple editors (like Notepad) will NOT detect changes to the file made by another program. This means that, if you have the file open in Notepad and make a change in APL, the file will be updated but Notepad will NOT notice. If you subsequently make changes in Notepad and save the file, you will lose the changes made previously in APL.

If you save a change in Notepad and subsequently edit the file in APL, you will be warned when you try to save the file from APL that the source file has changed since it was loaded: If you get this warning you need to check what changes were made and find a way to merge these changes together.

• Continue to Samples: To read more about the index page.

• Return to the main MildServer page.