gi
Class Grammar.Semantics

java.lang.Object
  gi.Grammar.Semantics

Enclosing class:

Grammar

protected static class Grammar.Semantics

extends Object

This class implements Semantics embedded in productions and evaluated when interpreting.

Version:

1.2

Author:

© 1999-2004 Craig A. Rich <carich@csupomona.edu>

Constructor Summary

protected

Grammar.Semantics() Constructs Semantics.

Method Summary

protected void

f(Grammar.ParseTree t, int l) Evaluates attributes in a ParseTree when interpreting.

Methods inherited from class java.lang.Object

clone, equals, finalize, getClass, hashCode, notify, notifyAll, toString, wait, wait, wait

Constructor Detail

Grammar.Semantics

protected Grammar.Semantics()

Constructs Semantics.

Method Detail

f

protected void f(Grammar.ParseTree t,
                 int l)
          throws Lexicon.Exception

Evaluates attributes in a ParseTree when interpreting. The semantic function f is invoked when a production containing this Semantics is applied to the ParseTree. t provides the context in which attribute evaluation occurs. t.root and t.child are the left and right side of the production in which this Semantics is embedded.

User-defined semantics are implemented by extending the class Semantics and overriding this method. The f method provided does nothing.

During top-down LL(1) parsing, the ParseTree is constructed from the top down by leftmost derivation. This is a depth-first left-to-right traversal, in which embedded Semantics are evaluated when first visited. Evaluation should not depend on attribute values produced by Semantics below or to the right of this Semantics. In other words, LL parsing supports evaluation of L-attributed semantic specifications.

During bottom-up LR(0), SLR(1) or LR(1) parsing, the ParseTree is constructed from the bottom up by reverse rightmost derivation. Embedded Semantics are evaluated after all subtrees rooted in the phrase to be reduced have been visited.

Parameters:

t - the ParseTree in which attribute evaluation occurs.

l - the index in t.child at which the Semantics being evaluated occurs. Introduced in version 1.1.

Throws:

Lexicon.Exception

Since:

1.1, renames evaluate in version 1.0.