Chapter 14
Preprocessor libraries
14.1
Introduction
Some people start to frown when you mention preprocessors. But most don’t even realize that when you compile C, you’re always using a preprocessor - and with good reason!
Without a preprocessor you really wouldn’t want to write C, it would be awkward. C++ started its life as a preprocessor
1
. Several Forth compilers won’t even compile without a preprocessor. Face it: there is nothing wrong with preprocessors!
Preprocessors are wonderful tools to hide awful constructs under a silky smooth syntax, enhance your productivity, simplify maintenance and prevent programming errors. 4tH comes with a preprocessor
2 that is more powerful than C’s and shares many characteristics with M4
3
, like:
• Recursive macro expansion;
• Text replacement;
• Parameter substitution;
• File inclusion;
• Conditional evaluation;
• Arithmetic expressions.
In order to further enhance it, 4tH provides preprocessor libraries, which are in fact predefined macro’s. You use a preprocessor library like you would use an ordinary one, e.g.: include 4pp/lib/standard.4pp
After you’ve run the preprocessor, you compile as usual. Note there is no protection against including a preprocessor library twice, but on the other hand it won’t be included by (or include) other libraries, so that is pretty academic. If you’re running a Unix-like Operating
System, you could use make to make your life a little easier, e.g. by defining the following rules:
1 http://www2.research.att.com/~bs/hopl2.pdf
2
See chapter 18 for more information.
3 http://en.wikipedia.org/wiki/M4_%28computer_language%29
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