Below are some frequently asked questions about the macro package. Click on the links below to navigate to the full question and answer content.
Q: R already has meta-programming capabilities. Why do you want to create a macro programming capability?
A: The macro package was motivated specifically for code generation. The goal is to generate a program where all variable values are resolved, and only the desired conditional code is included in the final program. This result requires a pre-processing and text replacement capability which is lacking in R. The macro package fills that need.
Q: It seems the R macro package provides less features than SAS. What capabilities does it provide?
A: The macro package supports the following features:
These features are the most essential features of the SAS macro language, and are missing from R. Other features are not needed for the primary use case of code generation, and are better handled using standard R code.
Q: I don’t quite get it. How am I supposed to use this package?
A: A macro-enabled R program is a standard R
program, with macro commands added as code comments. These special
comments act as pre-processor directives. These directives are resolved
by the pre-processor function msource(). What you will do
is write your macro enabled program, and run it with the
msource() function instead of the source()
function. Normally, you will do this on the command line. By default,
the msource() function will run the currently selected
program in RStudio. Otherwise, pass the name of the program you want to
run as the first parameter on msource(). The function will
pre-process the program, resolve any macro statements, and then execute
the resolved code.
Q: I want to create a macro function. Does the macro package support it? What about macro do loops?
A: No. Base R provides true function capabilities, and nothing would be gained by replicating that capability with macro functions. Likewise with do loops, there are already extensive features in Base R and Tidyverse for looping. It is recommended to use those existing features.
Q: I have a complicated set of conditions that are nested several levels deep. Can I do that with the macro package?
A: Yes. The package supports nest conditionals. There is no limit on the number of nested levels.
Q: I see from the documentation there is a “%include” macro function. How does it work? Is it the same as SAS?
A: Yes. The “#%include” macro function replicates the basic functionality of SAS “%include”. Text from the included file will be extracted and inserted into the generated file. Any macro statements in the included code will be resolved normally.
Q: In the documentation you mention that the macro package can be used as a code generator. How does that work?
A: To do code generation, simply supply an output
path as the second parameter on msource(). When the second
parameter is not supplied, the function will create a temporary output
file. When the second parameter is supplied, the function will output
the resolved code to the specified path. That file is the generated
code.
Q: There are several ways to do code generation in R already. Why would I want to use the macro package?
A: The advantages of using the macro package for code generation are: