19 Debugging Lisp Programs
There are several ways to find and investigate problems in an Emacs
Lisp program.
- If a problem occurs when you run the program, you can use the built-in
Emacs Lisp debugger (see The Lisp Debugger) to suspend the Lisp evaluator,
and examine and/or alter its internal state.
- You can use Edebug, a source-level debugger for Emacs Lisp.
See Edebug.
-
You can trace the execution of functions involved in the problem using
the tracing facilities provided by the trace.el package. This
package provides the functions
trace-function-foreground and
trace-function-background for tracing function calls, and
trace-values for adding values of select variables to the
trace. For the details, see the documentation of these facilities in
trace.el.
- If a syntactic problem is preventing Lisp from even reading the
program, you can locate it using Lisp editing commands.
- You can look at the error and warning messages produced by the byte
compiler when it compiles the program. See Compiler Errors.
- You can use the Testcover package to perform coverage testing on the
program.
- You can use the ERT package to write regression tests for the program.
See the ERT manual in ERT: Emacs Lisp Regression Testing.
- You can profile the program to get hints about how to make it more efficient.
See Profiling.
Other useful tools for debugging input and output problems are the
dribble file (see Terminal Input) and the open-termscript
function (see Terminal Output).