Typographical Conventions

Grammar

The Slang grammar in this document is presented using a variation of the Extended Backus–Naur form as follows:

Terminal symbol

'terminal' — terminal symbol spelled exactly as is within quotes
<regex> — terminal symbol expressed by a regular expression

Terminal symbols are those that can appear in the language. In the Slang language reference manual, two forms are used: literal strings that appear exactly as defined and symbols defined by regular expressions. Whitespace characters between terminal symbols are generally meaningless and ignored except where explicitly stated.

Non-terminal symbol

nonterminal

Non-terminal symbols do not appear in the language. They are used in defining production rules.

Production Rule

lhs = <expr>

A production rule defines how the left-hand-side non-terminal lhs may be substituted with the right-hand-side grammatical expression <expr>. The expression consists of non-terminals and terminals using the grammar expression building blocks described below.

Sometimes more than one production rule definitions are provided for the left-hand-side non-terminal. This means that the non-terminal may be substituted with any of the definitions, which is grammatically equivalent to alternation. Multiple production rules are used to associate semantics for individual production rules.

In case more multiple production rules may be successfully used, the semantics of the rule introduced earlier apply, unless explicit precedence (i.e., priority) is provided.

Note that a production rule definition is not explicitly terminated with a semi-colon (;).

Concatenation

lhs = symbol1 symbol2 … symbolN

Concatenation expresses a sequence of symbols, and it is expressed without a comma. Symbols may be terminal or non-terminal.

Alternation

lhs = alternative1 | alternative2

Alternation expresses alternative productions. That is, one (and exactly one) alternative is used.

Grouping

lhs = ( subexpr )

Grouping is used to denote the order of production.

Optional

lhs = [ subexpr ]

An optional subexpression may occur zero or one times in the production.

Repetition

lhs = expr*      — 0 or more times repetition
lhs = expr+      — 1 or more times repetition

A repeated expression occurs any number of times (* -repetition); or one or more times (+ -repetition).

(expr+) is equivalent to (expr expr*).

Precedence

The following precedence list is used in the production rule expressions:

Precedence	Grammar expressions	Description
Highest	( … ) [ … ]	grouping, optional
	* +	repetition
	symbol1 symbol2	concatenation (left-associative)
	symbol1 | symbol2	alternation (left-associative)
Lowest	=	production rule definition

For example, the following production rule definitions are equivalent:

lhs = expr1 expr2+ | expr3 [ expr4 expr5 ] expr6

lhs = (expr1 expr2+) | ((expr3 [ (expr4 expr5) ]) expr6)

Code Examples

Code examples are presented as follows.

Example:

struct ExampleStruct
{
    int a, b;
}

Remarks and Warnings

Remarks provide supplemental information such as recommendations, background information, rationale, and clarifications. Remarks are non-normative.

📝 Remark: Remarks provide useful information.

Warnings provide important information that the user should be aware of. For example, warnings call out experimental features that are subject to change and internal language features that should not be used in user code.

⚠️ Warning: Avoid using Slang internal language features. These exist to support Slang internal modules such as hlsl.meta.slang. Internal features are generally undocumented. They are subject to change without notice, and they may have caveats or otherwise not work as expected.