This document discusses meta languages and their use in describing the syntax of programming languages. Meta languages like railroad diagrams and BNF/EBNF allow language specifications to be understood by programmers and make it easier to learn new languages. Railroad diagrams use predefined elements and allowable paths to visually depict the structure of a language. The document provides an example railroad diagram for variable declarations in Visual Basic and discusses what additional elements like data types would need to be defined.

1. Kelly BauerMeta Languages

2. Why? Describes the syntax of a computer languageRules that govern the arrangement of elements in a languageeg. 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.

6. 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

7. 2 Basic Forms Railroad diagram (aka syntax structure diagrams)BNF/EBNF

8. Railroad diagrams

9. ElementsAllowable Paths

10. Pre defined langauge elements Eg, letter, sentence, program, variable nameVariable

11. Fixed Elements Reserved words, eg, Dim, -+, 0, 1DimAs

12. The elements can be combined to give optionsEg, A Boolean ConstantTF

13. Or to repeat elementsEg, A wordLetter

14. And these can then be combinedEg, a number that can be either positive or negativeDigit_

15. Textbook Pg 168 Defines the Winston language in railroad diagramsIs the following legitimate conditionsAbcd = +99

16. Abcd = +99Abcd 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 digitsThe statement follows the correct order of Identifier condition constantDavis, Sam (2008) Software Design and Development: The Preliminary Course, Parramatta Education Centre, Sydney

17. Abcd = +99Abcd 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 digitsThe statement follows the correct order of Identifier condition constant

18. Complete 2nd activity on pg 168TEXT ACTIVITY

19. an example

20. 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

21. PublicDimVariableAsData TypePrivateFrom this, what needs to be further defined?

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

23. SingleShortBooleanByteCharDateTimeDecimalDoubleIntLong

24. Variables in VBMust begin with an uppercase letterCan be lower or upper case or digits after first letter

25. Upper CaseLowerCaseUpperCaseDigit

26. 0987654321

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