An output_handler
handles the results of evaluate()
,
including the values, graphics, conditions. Each type of output is handled by
a particular function in the handler object.
new_output_handler(
source = identity,
text = identity,
graphics = identity,
message = identity,
warning = identity,
error = identity,
value = render,
calling_handlers = list()
)
A new output_handler
object
Function to handle the echoed source code under evaluation.
Function to handle any textual console output.
Function to handle graphics, as returned by
recordPlot()
.
Function to handle message()
output.
Function to handle warning()
output.
Function to handle stop()
output.
Function to handle the values returned from evaluation. If it only has one argument, only visible values are handled; if it has more arguments, the second argument indicates whether the value is visible.
List of calling handlers.
These handlers have precedence over the exiting handler installed
by evaluate()
when stop_on_error
is set to 0.
The handler functions should accept an output object as their first argument.
The return value of the handlers is ignored, except in the case of the
value
handler, where a visible return value is saved in the output
list.
Calling the constructor with no arguments results in the default handler, which mimics the behavior of the console by printing visible values.
Note that recursion is common: for example, if value
does any
printing, then the text
or graphics
handlers may be called.