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BNF and EBNF Grammar Analysis, Attribute Grammars, and AspectJ Pointcuts

This document presents a comprehensive examination of BNF and EBNF grammars, focusing on derivation processes and grammar transformation to EBNF. It poses challenges such as identifying language capabilities, explaining parse issues in if-statements, and correcting grammar problems in practice. Additionally, an introduction to attribute grammars is provided, demonstrating the construction of an attribute grammar that enforces conditions on elements. Lastly, it explores AspectJ through defining pointcuts for recursive and non-recursive calls and handling negative arguments in a Java Fibonacci method.

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BNF and EBNF Grammar Analysis, Attribute Grammars, and AspectJ Pointcuts

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  1. Exam 1 Review Questions CS 3360 Spring 2011

  2. BNF Consider the following BNF grammar. <sym-exp> -> <symbol> | <s-list> <s-list> -> ( ) | ( <sym-exp-list> ) <sym-exp-list> -> <sym-exp> | <sym-exp> <sym-exp-list> <symbol> -> x • Is the string ( x ( ) ) in the language described by the above grammar? Either show how to derive the string from the non-terminal <sym-exp> or briefly explain why no derivation is possible.

  3. BNF (Cont.) Consider the following BNF grammar. <sym-exp> -> <symbol> | <s-list> <s-list> -> ( ) | ( sym-exp-list ) <sym-exp-list> -> <sym-exp> | <sym-exp> <sym-exp-list> <symbol> -> x • Rewrite the grammar in E-BNF to reduce the number of rules

  4. BNF (Cont.) • Given the following language fragment described in EBNF: <statement> ::= <if-stmt> | <assign-stmt> <assign-stmt> ::= <ident> := <expression> <if-stmt> ::= if (<cond-expr>) <statement> [else <statement>] Consider the statement: if (a > b) if (a == 10) c := 1 else c := 2 The above grammar has a problem. Identify the problem and demonstrate it by showing how the if statement is parsed using the grammar. Explain how, in practice, this problem is solved.

  5. Attribute Grammars • Consider the following BNF grammar that defines a bag of elements, where each element is either x or y. Define an attribute grammar to permit only those bags that have more x's than y's; e.g., x, xyx, and xyxyx are sentences of the new language, but y, xy, and xxyyy are not. <bag> -> <elems> <elems> -> <elem> | <elem> <elems> <elem> -> x | y

  6. AspectJ Consider the following Java method. long fibo(int x) { return x <= 2 ? 1 : fibo(x – 2) + fibo(x – 1); } • Define pointcuts: (1) to denote all calls to fibo (2) to denote only recursive calls to fibo (3) to denote only non-recursive calls to fibo

  7. AspectJ (Cont.) • Define an aspect to print an error message when the fibo function is called with a negative argument. • Define an aspect to return factorial numbers instead for non-recursive calls to fibo with the probability of 0.5. (Hint: Use Math.random() to generate a random number in [0.0, 1.0))

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