2.3

The Syntactic Grammar

GRAMMARS

2.3   The Syntactic Grammar

The

syntactic grammar

 for Java is given in Chapters 4, 6 10, 14, and 15. This

grammar has Java tokens defined by the lexical grammar as its terminal symbols.

It defines a set of productions, starting from the goal symbol

CompilationUnit

( 7.3), that describe how sequences of tokens can form syntactically correct Java

programs.

A LALR(1) version of the syntactic grammar is presented in Chapter 19. The

grammar in the body of this specification is very similar to the LALR(1) grammar

but more readable.

2.4   Grammar Notation

Terminal symbols are shown in

fixed width

 font in the productions of the lexical

and syntactic grammars, and throughout this specification whenever the text is

directly referring to such a terminal symbol. These are to appear in a program

exactly as written.

Nonterminal symbols are shown in

italic

 type. The definition of a nonterminal

is introduced by the name of the nonterminal being defined followed by a colon.

One or more alternative right hand sides for the nonterminal then follow on suc 

ceeding lines. For example, the syntactic definition:

IfThenStatement:

if (

Expression

 )

Statement

states that the nonterminal

IfThenStatement

represents the token

if

, followed by a

left parenthesis token, followed by an

Expression

, followed by a right parenthesis

token, followed by a

Statement

. As another example, the syntactic definition:

ArgumentList:

Argument

ArgumentList

 ,

Argument

states that an

ArgumentList

 may represent either a single

Argument

 or an

ArgumentList

, followed by a comma, followed by an

Argument

. This definition of

ArgumentList

 is

recursive

, that is to say, it is defined in terms of itself. The result

is that an

ArgumentList

 may contain any positive number of arguments. Such

recursive definitions of nonterminals are common.

The subscripted suffix  

opt

 , which may appear after a terminal or nontermi 

nal, indicates an

optional symbol

. The alternative containing the optional symbol

actually specifies two right hand sides, one that omits the optional element and

one that includes it. This means that:

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