Set, unset or query the debugging flag on a function. The
condition arguments are the same as those that can be supplied via a call to
browser. They can be retrieved by the user once the browser has been entered, and provide a mechanism to allow users to identify which breakpoint has been activated.
debug(fun, text = "", condition = NULL) debugonce(fun, text = "", condition = NULL) undebug(fun) isdebugged(fun)
- any interpreted R function.
- a text string that can be retrieved when the browser is entered.
- a condition that can be retrieved when the browser is entered.
When a function flagged for debugging is entered, normal execution is suspended and the body of function is executed one statement at a time. A new browser context is initiated for each step (and the previous one destroyed).
At the debug prompt the user can enter commands or R expressions, followed by a newline. The commands are
- (or just an empty line, by default). Advance to the next step.
- continue to the end of the current context: e.g. to the end of the loop if within a loop or to the end of the function.
- synonym for
- print a stack trace of all active function calls.
- exit the browser and the current evaluation and return to the top-level prompt.
(Leading and trailing whitespace is ignored, except for an empty line).
Anything else entered at the debug prompt is interpreted as an R expression to be evaluated in the calling environment: in particular typing an object name will cause the object to be printed, and
ls() lists the objects in the calling frame. (If you want to look at an object with a name such as
n, print it explicitly.)
TRUE disables the use of an empty line as a synonym for
n. If this is done, the user will be re-prompted for input until a valid command or an expression is entered.
To debug a function is defined inside a function, single-step though to the end of its definition, and then call
debug on its name.
debug is persistent, and unless debugging is turned off the debugger will be entered on every invocation (note that if the function is removed and replaced the debug state is not preserved). Use
debugonce to enter the debugger only the next time the function is invoked.
The number of lines printed for the deparsed call when a function is entered for debugging can be limited by setting
When debugging is enabled on a byte compiled function then the interpreted version of the function will be used until debugging is disabled.
Documentation reproduced from R 3.0.1. License: GPL-2.