use_default: Apply a default value whenever a variable is not well-formed
Description
This function provides a functional approach for a specific use case
of conditional expressions: that of applying default values when
a variable is not well-formed. In this context, well-formedness is
considered to be any scalar value that is not NA.
By encapsulating this behavior in a
function, referential transparency is preserved.
Arguments
x
a scalar variable
default
the value to replace empty, NULL, or NA
Value
A well-formed value, either the original value or the default
if x is not well-formed.