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Error Trapping for APL Functions

IP.com Disclosure Number: IPCOM000045809D
Original Publication Date: 1983-Apr-01
Included in the Prior Art Database: 2005-Feb-07
Document File: 1 page(s) / 11K

Publishing Venue

IBM

Related People

Feeney, JW: AUTHOR

Abstract

Appropriate implementation of the described concept causes the execution of an APL function prior to allowing the user to get control in desk calculator mode. The APL function can then perform any error recovery actions necessary to prevent catastrophic failures.

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Error Trapping for APL Functions

Appropriate implementation of the described concept causes the execution of an APL function prior to allowing the user to get control in desk calculator mode. The APL function can then perform any error recovery actions necessary to prevent catastrophic failures.

The methodology employed to achieve this result consists of placing a call to the APL error-trapping function on the keyboard input stack at the start of the job to be protected. Whenever keyboard input is requested, this stacked call will be processed prior to accepting user input. Therefore, whenever the user is placed into desk calculator mode, the error-trapping function will get control. At that time, any necessary recovery actions can be taken. This could include restarting the job that was interrupted or returning control to the user in desk calculator mode.

To prevent the execution of this call during normal user input, the error trap call is placed on the stack using the LIFO (last-in, first-out) option. This means that it is placed so that it will be the first entry to be removed from the stack. Whenever normal input is to be requested from the user, the first entry is removed from the stack. Then, the input is requested from the user. Finally, the call to the error-trapping routine is placed back onto the stack after the user input is received. When all processing is completed, the call to the error-trapping function must be removed from the stack immediately p...