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Exam 1 Review Questions

Exam 1 Review Questions. CS 3360 Spring 2011. 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

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Exam 1 Review Questions

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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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