In order to use Edebug to debug Lisp code, you must first instrument the code. Instrumenting code inserts additional code into it, to invoke Edebug at the proper places.
Once you have loaded Edebug, the command C-M-x
(eval-defun) is redefined so that when invoked with a prefix
argument on a definition, it instruments the definition before
evaluating it. (The source code itself is not modified.) If the
variable edebug-all-defs is non-nil, that inverts the
meaning of the prefix argument: then C-M-x instruments the
definition unless it has a prefix argument. The default value of
edebug-all-defs is nil. The command M-x
edebug-all-defs toggles the value of the variable
edebug-all-defs.
If edebug-all-defs is non-nil, then the commands
eval-region, eval-current-buffer, and eval-buffer
also instrument any definitions they evaluate. Similarly,
edebug-all-forms controls whether eval-region should
instrument any form, even non-defining forms. This doesn't apply
to loading or evaluations in the minibuffer. The command M-x
edebug-all-forms toggles this option.
Another command, M-x edebug-eval-top-level-form, is available to
instrument any top-level form regardless of the values of
edebug-all-defs and edebug-all-forms.
While Edebug is active, the command I
(edebug-instrument-callee) instruments the definition of the
function or macro called by the list form after point, if is not already
instrumented. This is possible only if Edebug knows where to find the
source for that function; after loading Edebug, eval-region
records the position of every definition it evaluates, even if not
instrumenting it. See also the i command (see section Jumping), which
steps into the call after instrumenting the function.
Edebug knows how to instrument all the standard special forms,
interactive forms with an expression argument, anonymous lambda
expressions, and other defining forms. Edebug cannot know what a
user-defined macro will do with the arguments of a macro call, so you
must tell it; see section Instrumenting Macro Calls, for details.
When Edebug is about to instrument code for the first time in a
session, it runs the hook edebug-setup-hook, then sets it to
nil. You can use this to arrange to load Edebug specifications
(see section Instrumenting Macro Calls) associated with a package you are
using, but actually load them only if you use Edebug.
To remove instrumentation from a definition, simply re-evaluate its
definition in a way that does not instrument. There are two ways of
evaluating forms that never instrument them: from a file with
load, and from the minibuffer with eval-expression
(M-:).
If Edebug detects a syntax error while instrumenting, it leaves point
at the erroneous code and signals an invalid-read-syntax error.
See section Evaluation, for other evaluation functions available inside of Edebug.
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