LALR(1) GRAMMAR

Productions from  2.3: The Syntactic Grammar

19.2

PostfixExpression

 and ultimately to

Expression

 (for a parenthesized expression) or

to

ClassOrInterfaceType

 and then to

ReferenceType

 (for a cast). Therefore, the

productions shown above result in a grammar that is not LALR(1).

The solution is to eliminate the use of the nonterminal

ReferenceType

 in the

definition of

CastExpression

, which requires some reworking of both alternatives

to avoid other ambiguities:

CastExpression:

(

PrimitiveType Dims

opt

 )

UnaryExpression

(

Expression

 )

UnaryExpressionNotPlusMinus

(

Name Dims

 )

UnaryExpressionNotPlusMinus

This allows the parser to reduce

matthew

 to

Expression

 and then leave it there,

delaying the decision as to whether a parenthesized expression or a cast is in

progress. Inappropriate variants such as:

(int[])+3

and:

(matthew+1)baz

must then be weeded out and rejected by a later stage of compiler analysis.

The remaining sections of this chapter constitute a LALR(1) grammar for

Java syntax, in which the five problems described above have been solved.

19.2   Productions from  2.3: The Syntactic Grammar

Goal:

CompilationUnit

439