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### 38.3 Functions and Variables for Debugging

Option variable: debugmode

  Default value: `false`

  When `debugmode` is `true`, Maxima will start the Maxima debugger when a Maxima error occurs. At this point the user may enter commands to examine the call stack, set breakpoints, step through Maxima code, and so on. See `debugging` for a list of Maxima debugger commands.

  When `debugmode` is `lisp`, Maxima will start the Lisp debugger when a Maxima error occurs.

  In either case, enabling `debugmode` will not catch Lisp errors.

  Categories:Debugging ·Global flags ·

Option variable: refcheck

  Default value: `false`

  When `refcheck` is `true`, Maxima prints a message each time a bound variable is used for the first time in a computation.

  Categories:Evaluation ·Console interaction ·Global flags ·

Option variable: setcheck

  Default value: `false`

  If `setcheck` is set to a list of variables (which can be subscripted), Maxima prints a message whenever the variables, or subscripted occurrences of them, are bound with the ordinary assignment operator `:`, the `::` assignment operator, or function argument binding, but not the function assignment `:=` nor the macro assignment `::=` operators. The message comprises the name of the variable and the value it is bound to.

  `setcheck` may be set to `all` or `true` thereby including all variables.

  Each new assignment of `setcheck` establishes a new list of variables to check, and any variables previously assigned to `setcheck` are forgotten.

  The names assigned to `setcheck` must be quoted if they would otherwise evaluate to something other than themselves. For example, if `x`, `y`, and `z` are already bound, then enter

      setcheck: ['x, 'y, 'z]$

  to put them on the list of variables to check.

  No printout is generated when a variable on the `setcheck` list is assigned to itself, e.g., `X: 'X`.

  Categories:Console interaction ·Global flags ·

Option variable: setcheckbreak

  Default value: `false`

  When `setcheckbreak` is `true`, Maxima will present a break prompt whenever a variable on the `setcheck` list is assigned a new value. The break occurs before the assignment is carried out. At this point, `setval` holds the value to which the variable is about to be assigned. Hence, one may assign a different value by assigning to `setval`.

  See also `setcheck` and `setval`.

  Categories:Console interaction ·Global flags ·

System variable: setval

  Holds the value to which a variable is about to be set when a `setcheckbreak` occurs. Hence, one may assign a different value by assigning to `setval`.

  See also `setcheck` and `setcheckbreak`.

  Categories:Console interaction ·Global variables ·

Function: timer (f_1, …, f_n)
`timer` (all)
`timer` ()

  Given functions f_1, …, f_n, `timer` puts each one on the list of functions for which timing statistics are collected. `timer(f)$ timer(g)$` puts `f` and then `g` onto the list; the list accumulates from one call to the next.

  `timer(all)` puts all user-defined functions (as named by the global variable `functions`) on the list of timed functions.

  With no arguments, `timer` returns the list of timed functions.

  Maxima records how much time is spent executing each function on the list of timed functions. `timer_info` returns the timing statistics, including the average time elapsed per function call, the number of calls, and the total time elapsed. `untimer` removes functions from the list of timed functions.

  `timer` quotes its arguments. `f(x) := x^2$ g:f$ timer(g)$` does not put `f` on the timer list.

  If `trace(f)` is in effect, then `timer(f)` has no effect; `trace` and `timer` cannot both be in effect at the same time.

  See also `timer_devalue`.

  Categories:Debugging ·

Function: untimer (f_1, …, f_n)
`untimer` ()

  Given functions f_1, …, f_n, `untimer` removes each function from the timer list.

  With no arguments, `untimer` removes all functions currently on the timer list.

  After `untimer (f)` is executed, `timer_info (f)` still returns previously collected timing statistics, although `timer_info()` (with no arguments) does not return information about any function not currently on the timer list. `timer (f)` resets all timing statistics to zero and puts `f` on the timer list again.

  Categories:Debugging ·

Option variable: timer_devalue

  Default value: `false`

  When `timer_devalue` is `true`, Maxima subtracts from each timed function the time spent in other timed functions. Otherwise, the time reported for each function includes the time spent in other functions. Note that time spent in untimed functions is not subtracted from the total time.

  See also `timer` and `timer_info`.

  Categories:Debugging ·Global flags ·

Function: timer_info (f_1, ..., f_n)
`timer_info` ()

  Given functions f_1, ..., f_n, `timer_info` returns a matrix containing timing information for each function. With no arguments, `timer_info` returns timing information for all functions currently on the timer list.

  The matrix returned by `timer_info` contains the function name, time per function call, number of function calls, total time, and `gctime`, which meant "garbage collection time" in the original Macsyma but is now always zero.

  The data from which `timer_info` constructs its return value can also be obtained by the `get` function:

      get(f, 'calls);  get(f, 'runtime);  get(f, 'gctime);

  See also `timer`.

  Categories:Debugging ·

Function: trace (f_1, …, f_n)
`trace` (all)
`trace` ()

  Given functions f_1, …, f_n, `trace` instructs Maxima to print out debugging information whenever those functions are called. `trace(f)$ trace(g)$` puts `f` and then `g` onto the list of functions to be traced; the list accumulates from one call to the next.

  `trace(all)` puts all user-defined functions (as named by the global variable `functions`) on the list of functions to be traced.

  With no arguments, `trace` returns a list of all the functions currently being traced.

  The `untrace` function disables tracing. See also `trace_options`.

  `trace` quotes its arguments. Thus, `f(x) := x^2$ g:f$ trace(g)$` does not put `f` on the trace list.

  When a function is redefined, it is removed from the timer list. Thus after `timer(f)$ f(x) := x^2$`, function `f` is no longer on the timer list.

  If `timer (f)` is in effect, then `trace (f)` has no effect; `trace` and `timer` can’t both be in effect for the same function.

  Categories:Debugging ·

Function: trace_options (f, option_1, …, option_n)
`trace_options` (f)

  Sets the trace options for function f. Any previous options are superseded. `trace_options (f, ...)` has no effect unless `trace (f)` is also called (either before or after `trace_options`).

  `trace_options (f)` resets all options to their default values.

  The option keywords are:

  - `noprint` Do not print a message at function entry and exit.
  - `break` Put a breakpoint before the function is entered, and after the function is exited. See `break`.
  - `lisp_print` Display arguments and return values as Lisp objects.
  - `info` Print `-> true` at function entry and exit.
  - `errorcatch` Catch errors, giving the option to signal an error, retry the function call, or specify a return value.

  Trace options are specified in two forms. The presence of the option keyword alone puts the option into effect unconditionally. (Note that option foo is not put into effect by specifying `foo: true` or a similar form; note also that keywords need not be quoted.) Specifying the option keyword with a predicate function makes the option conditional on the predicate.

  The argument list to the predicate function is always `[level, direction, function, item]` where `level` is the recursion level for the function, `direction` is either `enter` or `exit`, `function` is the name of the function, and `item` is the argument list (on entering) or the return value (on exiting).

  Here is an example of unconditional trace options:

      (%i1) ff(n) := if equal(n, 0) then 1 else n * ff(n - 1)$

      (%i2) trace (ff)$

      (%i3) trace_options (ff, lisp_print, break)$

      (%i4) ff(3);

  Here is the same function, with the `break` option conditional on a predicate:

      (%i5) trace_options (ff, break(pp))$

      (%i6) pp (level, direction, function, item) := block (print (item),
          return (function = 'ff and level = 3 and direction = exit))$

      (%i7) ff(6);

  Categories:Debugging ·

Function: untrace
`untrace` (f_1, …, f_n)
`untrace` ()

  Given functions f_1, …, f_n, `untrace` disables tracing enabled by the `trace` function. With no arguments, `untrace` disables tracing for all functions.

  `untrace` returns a list of the functions for which it disabled tracing.

  Categories:Debugging ·

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