--- title: About the Language Reference framework: swift-book role: article path: swift-book/ReferenceManual/AboutTheLanguageReference --- # About the Language Reference Read the notation that the formal grammar uses. ## How to Read the Grammar The notation used to describe the formal grammar of the Swift programming language follows a few conventions: - An arrow (→) is used to mark grammar productions and can be read as "can consist of." - Syntactic categories are indicated by *italic* text and appear on both sides of a grammar production rule. - Literal words and punctuation are indicated by **`boldface constant width`** text and appear only on the right-hand side of a grammar production rule. - Alternative grammar productions are separated by vertical bars (|). When alternative productions are too long to read easily, they're broken into multiple grammar production rules on new lines. - In a few cases, regular font text is used to describe the right-hand side of a grammar production rule. - Optional syntactic categories and literals are marked by a trailing question mark, *?*. As an example, the grammar of a getter-setter block is defined as follows: > Grammar of a getter-setter block: > > *getter-setter-block* → **`{`** *getter-clause* *setter-clause*_?_ **`}`** | **`{`** *setter-clause* *getter-clause* **`}`** This definition indicates that a getter-setter block can consist of a getter clause followed by an optional setter clause, enclosed in braces, *or* a setter clause followed by a getter clause, enclosed in braces. The grammar production above is equivalent to the following two productions, where the alternatives are spelled out explicitly: > Grammar of a getter-setter block: > > > *getter-setter-block* → **`{`** *getter-clause* *setter-clause*_?_ **`}`** \ > *getter-setter-block* → **`{`** *setter-clause* *getter-clause* **`}`**