[appendix]
= Syntax Specification

The normative specification of the ADL2 syntax is expressed in Antlr4 as a series of component grammars, shown below. This has been tested with the Antlr 4.9 implementation available from http://www.antlr.org[Antlr.org^]. The source files are available in two locations on Github - {openehr_adl_antlr}/tree/master/src/main/antlr/adl[adl-antlr repository^]. The ODIN grammar used in parts of an ADL archetype is not shown below, it can be found in the {openehr_odin}[openEHR ODIN specification^].

== ADL Outer Syntax

The following grammar expresses the outer syntax of ADL, i.e. the top-level structure of section keywords and initial identification lines in an ADL text.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/adl2.g4[]
--------

== cADL Syntax

The following grammar expresses the syntax of cADL composite types, i.e. the language of the `definition` section of an archetype.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/cadl2.g4[]
--------

== cADL Primitives Syntax

The following grammar defines the syntax of cADL primitives, which are used by cADL composites and also by ADL rules.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/cadl2_primitives.g4[]
--------

== Rules Syntax

The following expression grammar defines the syntax that may appear in the `rules` section of an archetype and also the assertions in Archetype slots.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/base_expressions.g4[]
--------

== Value types

The following grammar defines the syntax for the terminal types in ADL, which are derived from ODIN.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/odin_values.g4[]
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== Base Lexer

The following grammar defines lexer patterns of generic lexical tokens.

[source, antlr-java]
--------
include::{openehr_adl_antlr_include}/adl/base_lexer.g4[]
--------