Meta Languages Railroad Diagrams

Meta Languages. Railroad Diagrams for Prelim Software Design and Development

1. Kelly Bauer Meta Languages

2. Why? Describes the syntax of a computer language Rules that govern the arrangement of elements in a language eg . The ran cat OR The cat ran

3. Why not just learn the language? Programming languages are very complex. You cant possibly know every way to do everything that you want. The likelihood is that you won’t program in the language you learn.

4. Why not just learn the language? Programming languages are very complex. You cant possibly know every way to do everything that you want. The likelihood is that you won’t program in the language you learn. Allows language specifications be understood by programmers and allows more learnability between languages

5. 2 Basic Forms Railroad diagram (aka syntax structure diagrams) BNF/EBNF

6. Railroad diagrams

7. Elements Allowable Paths

8. Pre defined langauge elements Eg , letter, sentence, program, variable name Variable

9. Fixed Elements Reserved words, eg , Dim, -+, 0, 1 Dim As

10. The elements can be combined to give options Eg , A Boolean Constant T F

11. Or to repeat elements Eg , A word Letter

12. And these can then be combined Eg , a number that can be either positive or negative _ Digit

13. Textbook Pg 168 Defines the Winston language in railroad diagrams Is the following legitimate conditions Abcd = +99

14. Abcd = +99 Abcd is a legitimate identifier, because it starts with an uppercase followed by a number of lower case +99 is a legitimate constant because it is a negative followed by a number of digits The statement follows the correct order of Identifier condition constant Davis, Sam (2008) Software Design and Development: The Preliminary Course, Parramatta Education Centre, Sydney

15. Abcd = +99 Abcd is a legitimate identifier, because it starts with an uppercase followed by a number of lower case +99 is a legitimate constant because it is a negative followed by a number of digits The statement follows the correct order of Identifier condition constant

16. Complete 2 nd activity on pg 168 TEXT ACTIVITY

17. an example

18. In Visual Basic Construct a railroad diagram to describe a best practice, legal variable declaration. Should follow the following structure: Dim Public or Private Variable Name As Data Type

19. Dim Public Private Variable As Data Type From this, what needs to be further defined?

20. Data type In Visual Basic, this can be Boolean, Byte, Char, Date, Time, Decimal, Double, Int , Long, Object, Short, Single

21. Boolean Byte Char Date Time Decimal Double Int Long Short Single

22. Variables in VB Must begin with an uppercase letter Can be lower or upper case or digits after first letter

23. Upper Case LowerCase UpperCase Digit

24. 1 2 3 4 5 6 7 8 9

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