Reference through nil pointer?

[facultyofmusic]

I'm doing my ISP and i have this piano keyboard I have to make work. This part of the program is for the black piano buttons:

Turing:

import GUI var mainScreen : int := Window.Open ("position:65;50,graphics:900;600") var picID : int var blackKeyPlayButton : string %The Display Procedure %BLACK KEY RESPONSES proc playBlackResponse     play (blackKeyPlayButton) end playBlackResponse proc display     %The black keys     drawfillbox (127, 420, 157, 550, 7)     picID := Pic.New (127, 420, 152, 550)     var black_key_button1 : int := GUI.CreatePictureButton (127, 420, picID, playBlackResponse)     var black_key_button2 : int := GUI.CreatePictureButton (172, 420, picID, playBlackResponse)     var black_key_button3 : int := GUI.CreatePictureButton (255, 420, picID, playBlackResponse)     var black_key_button4 : int := GUI.CreatePictureButton (300, 420, picID, playBlackResponse)     var black_key_button5 : int := GUI.CreatePictureButton (343, 420, picID, playBlackResponse)     loop         if GUI.GetEventWidgetID = black_key_button1 then             blackKeyPlayButton := "c+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "d+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "f+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "g+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "a+"         end if         exit when GUI.ProcessEvent     end loop end display display

The problem is that when I run it, it Widget thingy pops up and shows me a error. Which says "reference through nil pointer". What does this mean? What part of the program is wrong? Thanks for your help


Mod Edit: Remember to use syntax tags! Thanks

code:

[syntax="turing"]Code Here[/syntax]

[octopi]

If you try to access an object which hasn't been created yet, then you'll get this error. I'm not too familiar with Turing, and I can't find the error in your code, does the program point to a certain line as the cause of the problem?

Can you access a procedure without putting ()'s on the end of it?
playBlackResponse()

Also...

Turing:

if GUI.GetEventWidgetID = black_key_button1 then             blackKeyPlayButton := "c+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "d+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "f+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "g+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "a+"         end if

should be: shouldn't it?

Turing:

if GUI.GetEventWidgetID = black_key_button1 then             blackKeyPlayButton := "c+"         elsif GUI.GetEventWidgetID = black_key_button2 then             blackKeyPlayButton := "d+"         elsif GUI.GetEventWidgetID = black_key_button3 then             blackKeyPlayButton := "f+"         elsif GUI.GetEventWidgetID = black_key_button4 then             blackKeyPlayButton := "g+"         elsif GUI.GetEventWidgetID = black_key_button5 then             blackKeyPlayButton := "a+"         end if

Sorry I can't be more help, I really don't know Turing, perhaps another user can help you out more.

btw: those syntax tags are pretty touchy...

[Clayton]

Think of it this way, if no event has happened yet, then how could GetEventWidgetID possibly have any sort of value? You need to include that in your action procedure from the button.