Table of Contents
A list of mapping tags that ADD/MAP/REPLACE should be able to operate on even though they were present on readings in the input stream.
REOPEN-MAPPINGS = @a @b @c ;
You can affect how the grammar should be parsed with OPTIONS += ... ;.
Currently options can only be added, hence +=, but removing and assignment can be implemented if needed.
OPTIONS += no-inline-templates ;
Adds rule flag SAFE to all SETPARENT rules, meaning they won't run on cohorts that already have a parent. Can be countered per-rule with flag UNSAFE.
Disallows the use of inline sets in most places. They're still allowed in places that CG-2 did not consider sets, such as MAP, ADD, REPLACE, and ADDCOHORT tag lists, and in the context of a SET definition. Also, the special set (*) remains valid.
Disallows the use of inline templates in most places. They're still allowed in the context of a TEMPLATE definition.
Inverts the behavior of barriers on self tests. By default, barriers will stop if the self cohort matches. This can be toggled on a per context basis with modifier N, where self-no-barrier inverts the behavior of S vs. SN.
INCLUDE loads and parses another grammar file as if it had been pasted in on the line of the INCLUDE statement, with the exception that line numbers start again from 1. Included rules can thus conflict with rules in other files if they happen to occupy the same line in multiple files. It will still work as you expect, but --trace output won't show you which file the rules come from.
INCLUDE other-file-name ;
The file name should not be quoted and the line must end with semi-colon.
On Posix platforms the path will be shell expanded if it contains any of ~ $ *.
The include candidate will be looked for at a path relative to the file performing the include.
Be careful not to make circular includes as they will loop forever.
If you use option STATIC, only the passive parts of the grammar is loaded.
This is useful if you have an existing grammar that you don't want to split, but still want to reuse the sets
from it for other grammars. This is transitive - all grammars loaded from a static grammar will be static, even
if not explicitly loaded as such.
INCLUDE STATIC other-file-name ;
CG-2 has three seperate grammar sections: SETS, MAPPINGS, and CONSTRAINTS. VISLCG added to these with the CORRECTIONS section. Each of these can only contain certain definitions, such as LIST, MAP, or SELECT. As I understand it, this was due to the original CG parser being written in a language that needed such a format. In any case, I did not see the logic or usability in such a strict format. VISL CG-3 has a single section header SECTION, which can contain any of the set or rule definitions. Sections can also be given a name for easier identification and anchor behavior, but that is optional. The older section headings are still valid and will work as expected, though.
By allowing any set or rule definition anywhere you could write a grammar such as:
DELIMITERS = "<$.>" ;
LIST ThisIsASet = "<sometag>" "<othertag>" ;
SECTION
LIST ThisIsAlsoASet = atag btag ctag ;
SET Hubba = ThisIsASet - (ctag) ;
SELECT ThisIsASet IF (-1 (dtag)) ;
SECTION with-name;
LIST AnotherSet = "<youknowthedrill>" ;
MAP (@bingo) TARGET AnotherSet ;
Notice that the first LIST ThisIsASet is outside a section. This is because sets are considered global regardless of where they are declared and can as such be declared anywhere, even before the DELIMITERS declaration should you so desire. A side effect of this is that set names must be unique across the entire grammar, but as this is also the behavior of CG-2 and VISLCG that should not be a surprise nor problem.
Rules are applied in the order they are declared. In the above example that would execute SELECT first and then the MAP rule.
Sections may optionally have rule options (flags) which will be inherited by all rules within that section. Each new section resets this list. In order to parse the section name from rule options, the list of rule options must come after a : with space before it.
See BEFORE-SECTIONS. Takes the place of what previously were the MAPPINGS and CORRECTIONS blocks, but may contain any rule type.
See SECTION. Takes the place of what previously were the CONSTRAINTS blocks, but may contain any rule type.
See AFTER-SECTIONS. May contain any rule type, and is run once after all other sections. This is new in CG-3.
See NULL-SECTION. May contain any rule type, but is not actually run. This is new in CG-3.
The order and arrangement of BEFORE-SECTIONS and AFTER-SECTIONS in the grammar has no impact on the order normal SECTIONs are applied in.
An order of
SECTION
SECTION
BEFORE-SECTIONS
SECTION
NULL-SECTION
AFTER-SECTIONS
SECTION
BEFORE-SECTIONS
SECTION
is equivalent to
BEFORE-SECTIONS
SECTION
SECTION
SECTION
SECTION
SECTION
AFTER-SECTIONS
NULL-SECTION
In VISL CG-3, the --sections flag is able to specify ranges of sections to run, and can even be used to skip sections. If only a single number N is given it behaves as if you had written 1-N.
While it is possible to specify a range such as 1,4-6,3 where the selection of sections is not ascending, the actual application order will be 1, 1:4, 1:4:5, 1:4:5:6, 1:3:4:5:6 - that is, the final step will run section 3 in between 1 and 4. This is due to the ordering of rules being adamantly enforced as ascending only. If you wish to customize the order of rules you will currently have to use JUMP or EXECUTE.
--sections 6
--sections 3-6
--sections 2-5,7-9,13-15