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Evaluate the expression
• The previous specification only indicates the success or
failure of a parser. No semantic action is associated with
grammar rules.
• To calculate the expression, we must add java code in
the grammar to carry out actions at various points.
• Form of the semantic action:
expr:e1 PLUS expr:e2
{: RESULT = new Integer(e1.intValue()+ e2.intValue()); :}
– Actions (java code) are enclosed within a pair {: :}
– Labels e2, e2: the objects that represent the corresponding terminal or nonterminal;
– RESULT: The type of RESULT should be the same as the type of the
corresponding non-terminals. e.g., expr is of type Integer, so RESULT is of
type integer.
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