EMS Manual

Compiled Filters
EMS Manual—426909-005
5-9
Basic Components
The compiler uses TACL to translate token names to token codes. The TACL process
used is the one that calls the compiler. For more information about the relationship
between the filter language and TACL, see The Filter Compiler on page 5-44.
Basic Components
This subsection describes the lexical elements of the filter language—such as names,
operators, and constants—without much discussion of their relationship to each other.
The following subsections describe the way these elements combine to form larger
structures and ultimately a complete filter specification.
Comments
If you include two dashes (--) on a line (but not inside a string), the rest of the line is a
comment. (You can write dashes in a string as is, without an escape character. In
strings, dashes do not start a comment.)
Use comments freely to improve the readability of your source files or compiler listings.
Although comments using the TACL comment characters == and { } improve the
readability of your source file, they do not affect the compiler listing of your source text.
TACL strips TACL comments out of the language text. They do not appear in the
compiler listing.
Escape Character (~)
If you require a TACL special character in the filter specification for a usage not
understood by TACL, you must precede that character (or character group) with a tilde
(~), the TACL escape character. Specifically, when you need these characters:
[ ] { | ==
Write them as:
~[ ~] ~{ ~| ~==
(TACL processes the filter specification before the compiler sees it. The tilde is not kept
in the string constant. It warns TACL not to treat these characters as TACL special
characters.)
Reserved Words
Do not use the keywords reserved for filter language use as identifiers either in
uppercase or lowercase characters.
Table 5-1. Reserved Words (page 1 of 2)
AND END MATCH SSIDLIST
BEGIN FAIL NOT THEN
BOOLEAN FALSE OPTIONAL TOKENPRESENT