In vetr: Trust, but Verify

You can combine templates with && / ||:

vet(numeric(1L) || NULL, NULL)
vet(numeric(1L) || NULL, 42)
vet(numeric(1L) || NULL, "foo")

Templates only check structure. When you need to check values use . to refer to the object:

vet(numeric(1L) && . > 0, -42)  # strictly positive scalar numeric
vet(numeric(1L) && . > 0, 42)

If you do use the . symbol in your vetting expressions in your packages, you will need to include utils::globalVariables(".") as a top-level call to avoid the "no visible binding for global variable '.'" R CMD check NOTE.

You can compose vetting expressions as language objects and combine them:

scalar.num.pos <- quote(numeric(1L) && . > 0)
foo.or.bar <- quote(character(1L) && . %in% c('foo', 'bar'))
vet.exp <- quote(scalar.num.pos || foo.or.bar)

vet(vet.exp, 42)
vet(vet.exp, "foo")
vet(vet.exp, "baz")

all_bw is available for value range checks (~10x faster than isTRUE(all(. >= x & . <= y)) for large vectors):

vet(all_bw(., 0, 1), runif(5) + 1)

There are a number of predefined vetting tokens you can use in your vetting expressions such as:

vet(NUM.POS, -runif(5))    # positive numeric; see `?vet_token` for others

Vetting expressions are designed to be intuitive to use, but their implementation is complex. We recommend you look at example(vet) for usage ideas, or at the ["Non Standard Evaluation" section of the vignette][3] for the gory details.