Lect 1.2.5 EBNF Worked Examples - 3 First example –...

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Lecture 1.2.5 EBNF Worked Examples
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Lecture 02.5 For the exams, you may be required to Write/evaluate EBNF syntax Draw syntax diagrams Two worked examples Nov 2007 exam paper , Question 1d Nov 2005 exam paper, Question 1a 2
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First example One commonly used format for displaying the amount of money is as follows: The amount starts with a leading dollar sign ($), an optional string of asterisks (*) (these are typically used on cheques to prevent fraud), a string of decimal digits, and an optional fractional part consisting of a decimal point (.), and two decimal digits. The string of digits to the left of the decimal point may consist of a single zero (0); otherwise it must not start with a zero.
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Unformatted text preview: 3 First example – Groups of three digits to the left of the decimal point are separated by a comma (,) – A few examples of the above format are as follows: • $**9,876,543.10 • $**567 • $*5 • $0 • $0.27 • Construct the EBNF specification for a language that recognizes the above format. 4 Second example • Consider the following BNF grammar rules 1. <S> ::= <A> 2. <A> ::= [<B>,<A>] 3. <A> ::= <B> 4. <B> ::= <C> 5. <B> ::= (<A>) 6. <C> ::= a 7. <C> ::= b 8. <C> ::= c • For each of the strings below, indicate whether they are valid or invalid according to the BNF grammar rules given on the left. i. (a) ii. [b] iii. ([a,b]) iv. [(a),b] v. [(a),[b,a]] 5...
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