debug {base} | R Documentation |
Set, unset or query the debugging flag on a function.
The text
and 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)
fun |
any interpreted R function. |
text |
a text string that can be retrieved when the browser is entered. |
condition |
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. The commands are
n
c
cont
c
.where
Q
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.)
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.
Using 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.
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"))
The number of lines printed for the deparsed call when a function is
entered for debugging can be limited by setting
options(deparse.max.lines)
.
browser
, trace
;
traceback
to see the stack after an Error: ...
message; recover
for another debugging approach.