add `$test()` method

[jmbarbone]

When condition is created, allow for a test() function to be included.

Users can then do something like:

my_condition <- condition(..., test = function(x, y) x > 1)
my_condition$test(x, y, ...))

Which, when TRUE, will pass ... to $message().

Or something like browser(expr = )a

Replaces

if (test()) {
  cnd(condition(...))
}

... would expr be evaluated in the parent frame?

# test would then be quoted?
my_condition <- condition(..., test = x != y)

foo <- function(x, y) {
  my_condition$test()
}

foo <- function(expr) {
  expr <- substitute(expr)
  function() list(foo = eval(expr, parent.frame(1)))
}

bar <- foo(x > 1)

fizz <- function(x) {
  bar()
} 

fizz(1)
#> $foo
#> [1] FALSE
fizz(2)
#> $foo
#> [1] TRUE

[jmbarbone]

or maybe

foo := condition(test = expr)

where, when expr evaluates to TRUE (within caller environment), then then \(...) cnd(foo(...)) is returned?

bar <- function(x, y) {
  foo$test()(...)
}

example_error := condition(
  function(x, y) sprintf("x cannot be larger than y: '%s', '%s'", x, y),
  test = expression(x > y)
)

check_numbers <- function(x, y) {
  example_error$test()(x = x, y = y)
  TRUE
}

check_numbers(1, 2)
#> TRUE

check_numbers(2, 1)
#> example_error/error
#> (foo/cnd::condition/error/condition)
#> x cannot be larger than y: '2', '1'

or, $test() doesn't actually need to be set...

example_error := condition(
  function(x, y) sprintf("x cannot be larger than y: '%s', '%s'", x, y)
)

check_numbers <- function(x, y) {
  example_error$test(x > y)(x = x, y = y)
  TRUE
}

check_numbers(1, 2)
#> TRUE

check_numbers(2, 1)
#> example_error/error
#> (foo/cnd::condition/error/condition)
#> x cannot be larger than y: '2', '1'