as_drake_filename: Converts an ordinary character string
into a filename understandable by drake.
Description
This function simply wraps single quotes around x.
Quotes are important in drake.
In workflow plan data frame commands,
single-quoted targets denote physical files,
and double-quoted strings are treated as ordinary string literals.
Usage
as_drake_filename(x)
Arguments
x
character string to be turned into a filename
understandable by drake (i.e., a string with literal
single quotes on both ends).
Value
A single-quoted character string: i.e., a filename
understandable by drake.