1.5 Preprocessors

An alternative approach to complexity management, particularly when constructing tables, setting mathematics, or drawing diagrams, lies in preprocessing. A preprocessor employs a domian-specific language to ease the generation of tables, equations, and so forth in terms that are convenient for human entry. Each preprocessor reads a document and translates relevant portions of it into GNU troff input. Command-line options to groff tell it which preprocessors to use.

groff provides preprocessors for laying out tables (tbl), typesetting equations (eqn), drawing diagrams (pic and grn), inserting bibliographic references (refer), and drawing chemical structures (chem). An associated program that is useful when dealing with preprocessors is soelim.

groff also supports grap, a preprocessor for drawing graphs. A free implementation of it can be obtained separately.¹

Unique to groff is the preconv preprocessor that enables GNU troff to handle documents in a variety of input encodings, including UTF-8. Unlike most preprocessors, preconv operates on its entire enput rather than transforming specially marked regions of a document.

Other preprocessors exist, but no free implementations are known. An example is ideal, which draws diagrams using a mathematical constraint language.