calc: Debugging Calc
4.11.4 Debugging Calc
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A few commands exist to help in the debugging of Calc commands. 
Programming, to see the various ways that you can write your own Calc
commands.
The ‘Z T’ (‘calc-timing’) command turns on and off a mode in which
the timing of slow commands is reported in the Trail. Any Calc command
that takes two seconds or longer writes a line to the Trail showing how
many seconds it took. This value is accurate only to within one second.
All steps of executing a command are included; in particular, time
taken to format the result for display in the stack and trail is
counted. Some prompts also count time taken waiting for them to be
answered, while others do not; this depends on the exact implementation
of the command. For best results, if you are timing a sequence that
includes prompts or multiple commands, define a keyboard macro to run
the whole sequence at once. Calc’s ‘X’ command (Keyboard
Macros) will then report the time taken to execute the whole macro.
Another advantage of the ‘X’ command is that while it is executing,
the stack and trail are not updated from step to step. So if you expect
the output of your test sequence to leave a result that may take a long
time to format and you don’t wish to count this formatting time, end
your sequence with a <DEL> keystroke to clear the result from the stack.
When you run the sequence with ‘X’, Calc will never bother to format the
large result.
Another thing ‘Z T’ does is to increase the Emacs variable
‘gc-cons-threshold’ to a much higher value (two million; the usual
default in Calc is 250,000) for the duration of each command. This
generally prevents garbage collection during the timing of the command,
though it may cause your Emacs process to grow abnormally large.
(Garbage collection time is a major unpredictable factor in the timing
of Emacs operations.)
Another command that is useful when debugging your own Lisp
extensions to Calc is ‘M-x calc-pass-errors’, which disables the error
handler that changes the “‘max-lisp-eval-depth’ exceeded” message to the
much more friendly “Computation got stuck or ran too long.” This handler
interferes with the Emacs Lisp debugger’s ‘debug-on-error’ mode. Errors
are reported in the handler itself rather than at the true location of
the error. After you have executed ‘calc-pass-errors’, Lisp errors will
be reported correctly but the user-friendly message will be lost.
Info Catalog
calc: Caches
calc: Troubleshooting Commands