Sunday, July 14, 2013

Beginnings of Visual Compilers


Beginnings of Visual Compilers

It occurred to me the other day that I may have been the inventor of the first Visual Compiler.

Sometime about 1976 while contracting at Lear Siegler I has occasion to work on the MCDU (Multifunction Control/Display Unit) software for a military aircraft. 

Up until the end of 1973 I had been software manager at Cascade Data - a small business computer manufacturer in Grand Rapids Michigan.  While with Cascade Data I developed along with a second person a RPG compiler for which I used techniques of Cheatham that I had picked up in a two week compiler construction summer course at Cornell.  I can't provide a full reference at the present time since the course materials are currently in another location.

While developing the software for the MCDU it occurred to me that I could use similar techniques to create a compiler to create tables to be traversed in response to key pushes that were made by the pilot in order to make selections via the MCDU display. 

Therefore, I create a Backus-Naur Form (BNF) syntax for MCDU entry to change the display due to particular Line Select Key and Mode Key pushes or to indicate that data entered in the scratchpad line of the MCDU should be selected as the new value of a particular field. 

This is quite similar to the current use of mouse clicks on buttons or other widgets of a Windows form and entry into a dialog box.


Then when a key was pushed on the MCDU, the portion of the table for the currently displayed page was looked up to determine the action associated with the key.  Then the action was executed.  The action might cause a new page to be displayed or, for instance, convert scratchpad data to a numeric value of a particular format, evaluate the converted data for within range and the like, and, if valid, cause a particular aircraft variable to be modified.  That is, one action for each particular key push event where each action performed a specified task.



Hence the action code had become more complicated due to the necessary logic to determine the reason that the action had been entered thus causing extended code validation as well as problems that had to be solved in order to release the new FMCS version.

Anyway, as with the current visual compilers such as Microsoft Visual Basic, C#, C++, and such there was an action routine for which the code was to be supplied associated with each widget.  With the current compilers, the programmer can place widgets into a display form and then click on them to allow for naming the action and supplying the code.  Then, when the compiled or interpreted program is run, clicking on the displayed widget causes the supplied code to be executed.

With the MCDUs, the MCDU has its standard configuration and my compiler created the internal tables (which the Visual compilers must do) to cause the associated action to be executed.


Therefore, unless someone comes along that did it prior to 1976, it seems to me that I can take credit for being the first to develop the concept.

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