4.2.2 ‘-1’: Turn on brief debugging mode (FWEAVE)

This option tells FWEAVE to display irreducible scrap sequences.

A scrap is a part of speech. The expression ‘x + y’ consists of three scraps: ‘x’ (an expression), ‘+’ (a binary operator), and ‘y’ (an expression). FWEAVE contains production rules such as “replace the combination ‘expr binop expr’ with ‘expr’.” If all goes well, the result of FWEAVE’s reduction process is ultimately just one scrap, such as ‘function’. If FWEAVE is left with more than one scrap at the end of a section, this is called an irreducible scrap sequence; ‘-1’ displays them.

Irreducible scrap sequences can arise either because the programmer made a mistake or because FWEAVE has not been taught the proper grammar.

While FWEAVE is reducing the scraps, it appends TeX macros that ultimately produce the pretty-printed output. Frequently people ask how to change the appearance of that output. Fundamentally, this is not possible at present; the grammar rules and the associated TeX are hard-coded. A completely general, user-customizable scheme is very complex and daunting; it has not been attempted.

This brief debugging mode can be turned on more locally by means of the ‘@1’ command. See AT1.