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% File src/library/base/man/debug.Rd
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% File src/library/base/man/debug.Rd
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% Part of the R package, https://www.R-project.org
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% Part of the R package, https://www.R-project.org
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% Copyright 1995-2014 R Core Team
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% Copyright 1995-2019 R Core Team
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% Distributed under GPL 2 or later
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% Distributed under GPL 2 or later
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\name{debug}
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\name{debug}
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\title{Debug a Function}
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\title{Debug a Function}
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\alias{debug}
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\alias{debug}
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%% can we describe what happens when it is turned off *inside* debugging ??
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%% can we describe what happens when it is turned off *inside* debugging ??
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}
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}
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\description{
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\description{
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Set, unset or query the debugging flag on a function.
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Set, unset or query the debugging flag on a function.
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The \code{text} and \code{condition} arguments are the same as those
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The \code{text} and \code{condition} arguments are the same as those
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that can be supplied via a call to \code{browser}. They can be retrieved
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that can be supplied via a call to \code{\link{browser}}. They can be retrieved
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by the user once the browser has been entered, and provide a mechanism to
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by the user once the browser has been entered, and provide a mechanism to
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allow users to identify which breakpoint has been activated.
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allow users to identify which breakpoint has been activated.
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}
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}
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\details{
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\details{
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When a function flagged for debugging is entered, normal execution
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When a function flagged for debugging is entered, normal execution
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is suspended and the body of function is executed one statement at a
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is suspended and the body of function is executed one statement at a
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time. A new browser context is initiated for each step (and the
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time. A new \code{\link{browser}} context is initiated for each step
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previous one destroyed).
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(and the previous one destroyed).
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At the debug prompt the user can enter commands or \R expressions,
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At the debug prompt the user can enter commands or \R expressions,
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followed by a newline. The commands are described in the
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followed by a newline. The commands are described in the
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\code{\link{browser}} help topic.
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\code{\link{browser}} help topic.
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To debug a function which is defined inside another function,
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To debug a function which is defined inside another function,
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single-step though to the end of its definition, and then call
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single-step through to the end of its definition, and then call
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\code{debug} on its name.
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\code{debug} on its name.
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If you want to debug a function not starting at the very beginning,
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If you want to debug a function not starting at the very beginning,
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use \code{\link{trace}(..., at = *)} or \code{\link{setBreakpoint}}.
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use \code{\link{trace}(..., at = *)} or \code{\link{setBreakpoint}}.
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Using \code{debug} is persistent, and unless debugging is turned off
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Using \code{debug} is persistent, and unless debugging is turned off
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the debugger will be entered on every invocation (note that if the
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the debugger will be entered on every invocation (note that if the
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function is removed and replaced the debug state is not preserved).
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function is removed and replaced the debug state is not preserved).
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Use \code{debugonce} to enter the debugger only the next time the
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Use \code{debugonce()} to enter the debugger only the next time the
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function is invoked.
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function is invoked.
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To debug an S4 method by explicit signature, use
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To debug an S4 method by explicit signature, use
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\code{signature}. When specified, signature indicates the method of
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\code{signature}. When specified, signature indicates the method of
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\code{fun} to be debugged. Note that debugging is implemented slightly
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\code{fun} to be debugged. Note that debugging is implemented slightly
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}
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}
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\value{
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\value{
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\code{debug} and \code{undebug} invisibly return \code{NULL}.
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\code{debug} and \code{undebug} invisibly return \code{NULL}.
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\code{isdebugged} returns \code{TRUE} if the function or method is
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\code{isdebugged} returns \code{TRUE} if the function or method is
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marked for debugging, and \code{FALSE} otherwise.
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marked for debugging, and \code{FALSE} otherwise.
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}
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}
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\seealso{
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\seealso{
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\code{\link{debugcall}} for conveniently debugging methods,
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\code{\link{debugcall}} for conveniently debugging methods,
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\code{\link{browser}}, \code{\link{trace}};
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\code{\link{browser}} notably for its \sQuote{\emph{commands}}, \code{\link{trace}};
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\code{\link{traceback}} to see the stack after an \code{Error: \dots}
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\code{\link{traceback}} to see the stack after an \code{Error: \dots}
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message; \code{\link{recover}} for another debugging approach.
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message; \code{\link{recover}} for another debugging approach.
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}
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}
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\examples{
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\examples{
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