4.8 Macros

Additive Macros

If the text string == (or nothing) follows the macro name, the expression

that follows is the entire text of the macro body. If the text string +=

follows the macro name, then more than one such definition is allowed

(but not required) in the document and the body of the macro consists of

the concatenation of all such expressions in the order in which they occur

in the input file. Such a macro is said to be additive and is 

additively

defined

. Thus a macro body can either be defined in one place using one

definition (using ==) or it can be 

distributed

  throughout the input file in a

sequence of one or more macro definitions (using +=). If neither == and

+= are present, FunnelWeb assumes a default of ==.

Macros attached to product files cannot be additively defined. Additively

defined macros can have parameter lists and @Z and @M attributes, but

these must be specified only in the first definition of the macro. However,

+= must appear in each definition.

Library Macros

An ordinary macro definition can have from zero to five @L library level

markers. These define the macro definition s library level. A macro having

a particular name may be defined up to once at each library level, and each

such definition may be multipart (additive). At tangle time, the definition

having the lowest library level is used, with all other definitions of the

same name being completely ignored. This feature allows the creation of

general purpose include files that contain macro definitions that can be

overridden by definitions of the same name in the including file. Similarly,

it allows the creation of include files containing macro definitions that

override definitions in the including file. How you use the library macro

feature is up to you.

In the example below, the ugly duckling macro will be expanded to swan

because the swan definition has the lowest library level.

@$@@M@L@L@{egg@}

@$@@M@{swan@}

@$@@M@L@{signet@}

Note that the library macro facility imposes no requirement on the order of

appearance of the various macros of the same name; all that matters is the

library level. This means that macros defined in an include file that is

included at the 

end

  of a main file can be overridden by macros appearing

earlier in the main file.

http://www.ross.net/funnelweb/reference/parser_macros.html (2 of 3) [3/3/2000 10:46:46 PM]