Checks if file exists using
vld_string(x) && file.exists(x) && !dir.exists(x)
Value
The chk_
function throws an informative error if the test fails or
returns the original object if successful so it can used in pipes.
The vld_
function returns a flag indicating whether the test was met.
See also
For more details about the use of this function,
please read the article
vignette("chk-families")
.