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To investigate a problem that happens in the middle of a program, one useful technique is to enter the debugger whenever a certain function is called. You can do this to the function in which the problem occurs, and then step through the function, or you can do this to a function called shortly before the problem, step quickly over the call to that function, and then step through its caller.
This function requests function-name to invoke the debugger each time
it is called. It works by inserting the form (debug 'debug)
into
the function definition as the first form.
Any function defined as Lisp code may be set to break on entry, regardless of whether it is interpreted code or compiled code. If the function is a command, it will enter the debugger when called from Lisp and when called interactively (after the reading of the arguments). You can’t debug primitive functions (i.e., those written in C) this way.
When debug-on-entry
is called interactively, it prompts
for function-name in the minibuffer.
If the function is already set up to invoke the debugger on entry,
debug-on-entry
does nothing.
Please note: if you redefine a function after using
debug-on-entry
on it, the code to enter the debugger is lost.
debug-on-entry
returns function-name.
(defun fact (n) (if (zerop n) 1 (* n (fact (1- n))))) ⇒ fact
(debug-on-entry 'fact) ⇒ fact
(fact 3)
------ Buffer: *Backtrace* ------ Entering: * fact(3) eval-region(4870 4878 t) byte-code("...") eval-last-sexp(nil) (let ...) eval-insert-last-sexp(nil) * call-interactively(eval-insert-last-sexp) ------ Buffer: *Backtrace* ------
(symbol-function 'fact) ⇒ (lambda (n) (debug (quote debug)) (if (zerop n) 1 (* n (fact (1- n)))))
This function undoes the effect of debug-on-entry
on
function-name. When called interactively, it prompts for
function-name in the minibuffer. If function-name is
nil
or the empty string, it cancels debugging for all functions.
If cancel-debug-on-entry
is called more than once on the same
function, the second call does nothing. cancel-debug-on-entry
returns function-name.
Next: Explicit Debug, Previous: Infinite Loops, Up: Debugger [Contents][Index]