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19.1.5 Entering the debugger when a variable is modified

Sometimes a problem with a function is due to a wrong setting of a variable. Setting up the debugger to trigger whenever the variable is changed is a quick way to find the origin of the setting.

Command: debug-on-variable-change variable ¶

This function arranges for the debugger to be called whenevervariable is modified.

It is implemented using the watchpoint mechanism, so it inherits the same characteristics and limitations: all aliases of variablewill be watched together, only dynamic variables can be watched, and changes to the objects referenced by variables are not detected. For details, see Running a function when a variable is changed..

Command: cancel-debug-on-variable-change &optional variable ¶

This function undoes the effect of debug-on-variable-change onvariable. When called interactively, it prompts forvariable in the minibuffer. If variable is omitted ornil, it cancels break-on-change for all variables. Callingcancel-debug-on-variable-change does nothing to a variable which is not currently set up to break on change.