2.4

Grammar Notation

GRAMMARS

which defines one right hand side for the nonterminal

ConstructorDeclaration

.

(This right hand side is an abbreviation for four alternative right hand sides,

because of the two occurrences of  

opt

 .)

When the words  one of   follow the colon in a grammar definition, they sig 

nify that each of the terminal symbols on the following line or lines is an alterna 

tive definition. For example, the lexical grammar for Java contains the production:

ZeroToThree: one of

0 1 2 3

which is merely a convenient abbreviation for:

ZeroToThree:

0

1

2

3

When an alternative in a lexical production appears to be a token, it represents

the sequence of characters that would make up such a token. Thus, the definition:

BooleanLiteral: one of

true false

in a lexical grammar production is shorthand for:

BooleanLiteral:

t r u e

f a l s e

The right hand side of a lexical production may specify that certain expan 

sions are not permitted by using the phrase  but not  and then indicating the

expansions to be excluded, as in the productions for

InputCharacter

 ( 3.4) and

Identifier

 ( 3.8):

InputCharacter:

UnicodeInputCharacter

 but not

CR

 or

LF

Identifier:

IdentifierName

 but not a

Keyword

 or

BooleanLiteral

 or

NullLiteral

Finally, a few nonterminal symbols are described by a descriptive phrase in

roman type in cases where it would be impractical to list all the alternatives:

RawInputCharacter

:

any Unicode character

10