Debug a Function

Description

Set, unset or query the debugging flag on a function.

Usage

debug(fun)
undebug(fun)
isdebugged(fun)

Arguments

Details

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. The commands are

n

(or just return). Advance to the next step.

c

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.

cont

synonym for c.

where

print a stack trace of all active function calls.

Q

exit the browser and the current evaluation and return to the top-level prompt.

(Leading and trailing whitespace is ignored, except for return).

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.)

If a function is defined inside a function, single-step though to the end of its definition, and then call debug on its name.

In order to debug S4 methods (see Methods), you need to use trace, typically calling browser, e.g., as
trace("plot", browser, exit=browser, signature = c("track", "missing"))

See Also

browser, trace; traceback to see the stack after an Error: ... message; recover for another debugging approach.