Programming Language

1
Chapter 2.2

• Programming Language
• Definition

2
Summary

• Syntax and Semantics
• Semantics definition
• Denotational Semantics
• Elementary actions
• Syntax definitions
• Backus-Naur Formalism
• Syntax diagrams

3
Syntax and Semantics

• Syntax form
• Semantics meaning
• Example
• My beer is on the table
• Syntax OK
• Semantics OK
• My table is on the beer
• Syntax OK
• Semantics You had too many beers !!!

4
Summary

• Syntax and Semantics
• Semantics definition
• Denotational Semantics
• Elementary actions
• Syntax definitions
• Backus-Naur Formalism
• Syntax diagrams

5
Summary

• Syntax and Semantics
• Semantics definition
• Denotational Semantics
• Elementary actions
• Syntax definitions
• Backus-Naur Formalism
• Syntax diagrams

6
Backus Naur Formalism (BNF)

• Terminal Symbols
• Appear literally in program text
• Examples a, 3, END, gt,
• Non-terminal Symbols
• Name given to set of terminal symbols
• Written between lt and gt
• Defined by a metalinguistic expression
• Examples ltLettergt , ltDigitgt,ltExpressiongt,ltModule
  gt
• Metalinguistic expression
• Formal definition () of a non-terminal symbol
• Contains terminal and non-terminal symbols
• Expresses juxtaposition or choice (the
  operator)
• Example ltDigitgt 0123456789

7
Backus Naur Formalism (BNF)Examples

• ltUpperCaseLettergt ABCDE
  XYZ
• ltLowerCaseLettergt abcde
  xyz
• ltLettergt ltUpperCaseLettergt
  ltLowerCaseLettergt
• ltDigitgt 1234567890
• ltCardinalNumbergt ltDigitgt ltDigitgtltCardinalNum
  bergt
• ltIntegerNumbergt ltCardinalNumbergt
• ltCardinalNumbergt
• - ltCardinalNumbergt
• ltIdentifiergt ltLettergt
  ltIdentifiergtltLettergt ltIdentifiergt ltDigitgt

8
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it a digit ?
• Certainly not

9
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?

10
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it a digit ?
• Certainly not

11
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it Digit followed by a CardinalNumber ?
• Is 3 a Cardinal Number ?

12
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it Digit followed by a CardinalNumber ?
• Is 3 a Cardinal Number ?
• Is it a digit ?
• YES

13
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it Digit followed by a CardinalNumber ?
• Is 3 a CardinalNumber ?
• Is it a digit ?
• YES
• As a consequence, 3 is a CardinalNumber

14
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it Digit followed by a CardinalNumber ?
• Is 3 a CardinalNumber ?
• Is it a digit ?
• YES
• As a consequence, 3 is a CardinalNumber
• As a consequence, 23 is a CardinalNumber

15
ltCardinalNumbergt ltDigitgt
ltDigitgtltCardinalNumbergt

• Is 123 a CardinalNumber ?
• Is it Digit followed by a CardinalNumber ?
• Is 23 a Cardinal Number ?
• Is it Digit followed by a CardinalNumber ?
• Is 3 a CardinalNumber ?
• Is it a digit ?
• YES
• As a consequence, 3 is a CardinalNumber
• As a consequence, 23 is a CardinalNumber
• As a consequence, 123 is a CardinalNumber

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ltIdentifiergt ltLettergt ltIdentifiergtltLettergt
ltIdentifiergt ltDigitgt

• Correct identifiers
• Length, Width, Cost, ...
• MySalary, NumberOfStudents, Year1,
• X1, Y2, A1, A5,
• Incorrect identifiers
• My Salary, Number-of-students,
• 1stYear, ...

17
Syntax Definition
Non-recursive BNF
Syntax diagram
BNF


Definition
Diagram
Choice
0 or 1 occurrence

0, 1 or many occurrences

18
Syntax Definition
Non-recursive BNF
Syntax diagram
BNF


Definition
Diagram
Choice
0 or 1 occurrence

0, 1 or many occurrences

19
Backus Naur Formalism (BNF)Examples

• ltUpperCaseLettergt ABCDE
  XYZ
• ltLowerCaseLettergt abcde
  xyz
• ltLettergt ltUpperCaseLettergt
  ltLowerCaseLettergt
• ltDigitgt 1234567890
• ltCardinalNumbergt ltDigitgt ltDigitgt
• ltIntegerNumbergt -ltCardinalNumbergt
• ltIdentifiergt ltLettergt ltLettergtltDigitgt

20
Summary

• Syntax and Semantics
• Semantics definition
• Denotational Semantics
• Elementary actions
• Syntax definitions
• Backus-Naur Formalism
• Syntax diagrams

21
Backus Naur Formalism (BNF)

• Terminal Symbols
• Non-terminal Symbols
• Metalinguistic expression
• Railroad diagrams with semaphores requiring
  specific symbols to grant passage.
• The defined non-terminal symbol leaves all its
  symbols, in the order of occurrence, at
  appropriate semaphores and reaches the exit with
  none left.

Terminal symbol
Non-terminal symbol
22
Syntax Definition
Non-recursive BNF
Syntax diagram
BNF


Definition
Diagram
Choice
0 or 1 occurrence

0, 1 or many occurrences

23
Syntax DiagramsExamples

• Letter

24
Syntax DiagramsExamples
Digit
ltDigitgt 0123456789
CardinalNumber
ltCardinalNumbergt ltDigitgt ltDigitgt
Digit
Digit
25
Syntax DiagramsExamples
IntegerNumber
ltIntegerNumbergt - ltCardinalNumbergt
CardinalNumber
26
Syntax DiagramsExamples
Identifier
ltIdentifiergt ltLettergt ltLettergtltDigitgt
27
Syntax DiagramsExample from the Modula 2 syntax