1. What are the names of the Meta Languages you have used?
What are they?
What do you use them for?
What are the names of the Meta Languages you have used?

2. Meta Languages – What are they?
Text based methods of describing rules of a language.
Are precise
Always mean the same thing ie, 2+2 = 4

3. Meta Languages – what are they used for?
To describe more complex programming languages
Help programmers with language design & implementation
Represent the SYNTAX of programming languages (the rules of a language)

4. Meta Languages – you need to know these types:
Text-based metalanguages:
BNF – Backus Normal Form
EBNF – Extended Backus-Naur Form
Graphically-based metalanguages:
Railroad Diagrams (also known as syntax structure diagrams)

5. What is the difference between BNF and EBNF?
BNF is very basic
Shows language elements within brackets <>
Allows use of terminal symbols like * or –
Includes Alternatives |
EBNF was developed to EXTEND BNF in order to include
Repitition { }
Optional elements [ ]
Grouped Elements ( )
Simpler symbol for ‘is defined as’ EBNF uses = BNF uses ::=

6. Examples
BNF Digit ::= 1 | 2 | 3 Number ::= <digit> * <digit>
EBNF Digit = 1 | 2 | 3 Number = <digit> * <digit>
Railroad Diagram refer to Table 5.2 in Wilson, p125

7. Worked Example
Decide which of the following are legal and which are illegal. Give a reason for your answer Digit ::= 4 | 5 | 6 | 7 | 8 Sum ::= <Digit> * <Digit>
Sum = 4 * 8
Sum = 7 * 5
Sum = 9 * 6
Sum = 5 * 4
Sum = 6 * 1
What type of metalanguage was used above?

8. In Class Questions Exercise 5.1 (from Wilson, p124) Questions 3 & 4
Exercise 5.1 (from Fowler, p164) Questions 3a) 3b) 4 and 7