on.exit: Function Exit Code

In robertzk/monadicbase: The R Base Package

Description

on.exit records the expression given as its argument as needing to be executed when the current function exits (either naturally or as the result of an error). This is useful for resetting graphical parameters or performing other cleanup actions.

If no expression is provided, i.e., the call is on.exit(), then the current on.exit code is removed.

Usage

on.exit(expr = NULL, add = FALSE)

Arguments

expr	an expression to be executed.
add	if TRUE, add expr to be executed after any previously set expressions; otherwise (the default) expr will overwrite any previously set expressions.

Details

The expr argument passed to on.exit is recorded without evaluation. If it is not subsequently removed/replaced by another on.exit call in the same function, it is evaluated in the evaluation frame of the function when it exits (including during standard error handling). Thus any functions or variables in the expression will be looked for in the function and its environment at the time of exit: to capture the current value in expr use substitute or similar.

This is a ‘special’ primitive function: it only evaluates the argument add.

Value

Invisible NULL.

References

Becker, R. A., Chambers, J. M. and Wilks, A. R. (1988) The New S Language. Wadsworth & Brooks/Cole.

See Also

sys.on.exit which returns the expression stored for use by on.exit() in the function in which sys.on.exit() is evaluated.

Examples

require(graphics)

opar <- par(mai = c(1,1,1,1))
on.exit(par(opar))

robertzk/monadicbase documentation built on May 27, 2019, 10:35 a.m.