\HeaderA{traceback}{Print Call Stacks}{traceback}
\aliasA{.Traceback}{traceback}{.Traceback}
\keyword{programming}{traceback}
\begin{Description}\relax
By default, \code{traceback()} prints the call stack of the last
uncaught error, i.e., the sequence of calls that lead to the error.
This is useful when an error occurs with an unidentifiable error
message.  It can also be used to print arbitrary lists of deparsed
calls.
\end{Description}
\begin{Usage}
\begin{verbatim}
traceback(x = NULL)
\end{verbatim}
\end{Usage}
\begin{Arguments}
\begin{ldescription}
\item[\code{x}] \code{NULL} (default), or a list or pairlist of deparsed
calls.
\end{ldescription}
\end{Arguments}
\begin{Details}\relax
The stack of the last uncaught error is stored as a list of deparsed
calls in \code{.Traceback}, which \code{traceback} prints in a
user-friendly format.

Errors which are caught \emph{via} \code{\LinkA{try}{try}} or
\code{\LinkA{tryCatch}{tryCatch}} do not generate a traceback, so what is printed
is the call sequence for the last uncaught error, and not necessarily
the last error.
\end{Details}
\begin{Value}
\code{traceback()} returns nothing, but prints the deparsed call stack
deepest call first.  The calls may print on more that one line, and
the first line is labelled by the frame number.
\end{Value}
\begin{References}\relax
Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988)
\emph{The New S Language}.
Wadsworth \& Brooks/Cole.
\end{References}
\begin{Examples}
\begin{ExampleCode}
foo <- function(x) { print(1); bar(2) }
bar <- function(x) { x + a.variable.which.does.not.exist }
## Not run: 
foo(2) # gives a strange error
traceback()
## End(Not run)
## 2: bar(2)
## 1: foo(2)
bar
## Ah, this is the culprit ...
\end{ExampleCode}
\end{Examples}

