The m4 Macro Package

In this second example, we create a “database” of exam questions for a course. The goals are 1) to manage exam questions in a single repository, 2) to be able to create a LaTeX-format exam by simply choosing which questions to include and 3) to produce an answer key with equally little effort.

The question database consists of an m4 macro for each question. We store the macros in a file called questions.m4. For example:

define(`QUESTION_1',
  `Why did the chicken cross the road?
  ANSWER(1in, `To get to the other side')
')

Obviously, this macro will be expanded with the question itself, but note the use of the embedded macro ANSWER. It expands to one inch of vertical space if we're producing the exam, otherwise it expands to the answer if we're producing an answer key. ANSWER is defined as:

define(ANSWER, ifdef(`ANSWER_KEY', `Answer: $2',
`\vspace*{$1}'))

Using the question macros is as easy as using the HTML macros. The complete exam code is stored in a file called exam.m4:

include(examMacros.m4)
EXAM_HEADER(`JOKE 101', `Fall 2001',
`First Exam')
include(questions.m4)
QUESTION_1
QUESTION_2
EXAM_TRAILER

The “include” on line one includes the code for EXAM_HEADER and EXAM_TRAILER that generate boilerplate LaTeX at the top and bottom of the exam. Line three includes the question macros we just created. Lines four and five include two questions from the database.

To create an exam, we run the command m4 exam.m4 > exam.tex. Because ANSWER_KEY was never defined, each question will include space for an answer. To create an answer key, we use m4's command-line options to temporarily define an ANSWER_KEY macro:

m4 -DANSWER_KEY exam.m4 > exam.key.tex

m4 is a tool that has applications in an endless number of domains. Anywhere you want to reduce duplication of effort, m4 can help. It is feature-rich enough that you can do almost anything and produce any kind of content you may wish. I hope I've given you enough to whet your appetite for m4 and to give you an appreciation for what m4 can do for you. Happy macro writing!

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