Constructor of a terminator object

Terminator objects are used to write termination conditions that can be tested via a callback function within another function during its evaluation.

Usage

terminator(cond = FALSE, Delta = 1, print = TRUE, plotter = NULL, ...)

Arguments

cond: a termination condition. Either an expression or call that evaluates to a logical.
Delta: an integer specifying how often the termination condition is evaluated. Delta = 0 means never, and otherwise the condition is evaluated every Delta-th iteration. Delta = 1 is the default.
print: a variable name to print or a logical. If FALSE, nothing is printed. If a variable name is given, that variable (if it exists) will be printed every Delta-th iteration. If TRUE (the default) the last variable in cond is printed every Delta-th iteration.
plotter: an expression, possibly created by the plotter function.
...: other arguments passed to format for printing and plot.window

Value

A terminator object containing the functions terminator and clear.

Details

Terminator objects are similar to tracer objects but serve a different purpose. Like tracer objects, they can be used to trace, print and plot values of a variable within the evaluation environment of another function during its evaluation. The primary purpose of a terminator object is, however, to evaluate a termination condition, which can trigger termination of a loop. Terminator objects do not save trace information and do not trace runtime.

Examples

term <- terminator(quote(i >= 3), print = FALSE)

for (i in 1:5) {
  if (term$terminator()) {
    break
  }
}

i
#> [1] 3