Compiler Design

1. Compilers Design
Course
Dr. Ramadan Babers
Compilers Design – Lec7
Faculty of Science Helwan University
1st Term – 2017/2018

2. 2
Chapter 2
A Simple Syntax-Directed
Translator

3. 2.6.3 Constants
3
Ex: 123
v=0
v=0×10 + 1 -------1
v=1×10 + 2 -------12
v=12×10 + 3 -----123

4. 2.6.4 Recognizing Keywords and Identifiers
4

5. 2.6.5 A Lexical Analyzer
5
?

6. 2.6.5 A Lexical Analyzer
6
?

7. 2.6.5 A Lexical Analyzer
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?

8. 2.6.5 A Lexical Analyzer
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First Class (Token)

9. 2.6.5 A Lexical Analyzer
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Second Class (Num)

10. 2.6.5 A Lexical Analyzer
10
Third Class (Word)

11. 2.6.5 A Lexical Analyzer (Complete Java Code 1/2)
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12. 2.6.5 A Lexical Analyzer (Complete Java Code 2/2)
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13. 2.7 Symbol Tables
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 Symbol tables are data structures that are used by compilers to
hold information about source-program constructs.
 The information is collected incrementally by the analysis
phases of a compiler and used by the synthesis phases to
generate the target code.
 Symbol-table entries are created and used during the analysis
phase by the lexical analyzer, the parser, and the semantic
analyzer

14. 2.7.1 Symbol Table Per Scope
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15. 2.7.1 Symbol Table Per Scope
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{t1
{t2
}
{t3
{t4
}
}
}
t1
t2 t3
t4
Null
Env t1= new Env (Null)
Env t2= new Env (t1)
Env t3= new Env (t1)
Env t4= new Env (t3)

16. 2.7.1 Symbol Table Per Scope
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1/2

17. 2.7.1 Symbol Table Per Scope
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2/2

18. 2.7.2 The Use of Symbol Tables
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The use of symbol tables for translating a language with blocks
{ int x ; char y ; { bool y ; x ; y ; } x ; y ; }
the translation scheme strips the declarations and produces
{ { x : int ; y : bool ; } x : int ; y : char ; }

19. 2.7.2 The Use of Symbol Tables
19
program block
block ‘{‘ decls stmts ‘}’ | e
decl type id ;
stmts stmts stmt | e
stmt block | factor ;
factor id

20. 2.7.2 The Use of Symbol Tables
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21. Required
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{int x ; x ;}
{x : int ;}