C H A P T E R T W O

1. C H A P T E R T W O Syntax Programming Languages – Principles and Paradigms by Allen Tucker, Robert Noonan

2. Chomsky’s formal model: • Naom Chomsky developed a formal model of language types in the late 1950s. • Grammars were classified in a hierarchy of ascending complexity. • The original four classifications were: • Regular • Context-free • Context-sensitive • Unrestricted

3. Backus-Naur Form (BNF): • Created by John Backus and Peter Naur in 1960 to assist them in creating the programming language Algol. • Based on Chomsky’s work. • BNF works to describe context-free grammars. • More powerful than regular expressions.

4. Backus-Naur Form (BNF): BNF rules are used to rewrite nonterminal symbols into terminal symbols. Example rules: Integer -> Digit | Integer Digit Digit -> 0 | 1| 2 | 3 | 4 | 5 | 6 | 7 | 8 | 9

5. Parse Tree for 352 As an Integer Figure 2.1

6. BNF and Lexical Analysis: • A programming language’s lexicon is the set of all grammatical categories that define strings (tokens) from which a program may be written. • Typical categories include: • Operators (+, -, *, /, etc.) • Separators (;, ., {, }, etc.) • Keywords ( for, else, if, int, etc.) • Literals (numbers and string constants) • Identifiers (variable and function names)

7. A Program Fragment Viewed As a Stream of Tokens Figure 2.2

8. A Simple Lexical Syntax for a Small Language, Jay Figure 2.3

9. Major Stages in the Compiling Process Figure 2.4

10. Skeleton Lexical Analysis Method That Returns Tokens Figure 2.5

11. Regular Expressions and Lexical Analysis: • An alternative to BNF for specifying a language at the lexical level. • Widely used as a tool for lexical scanners (routines that create token strings). • Not powerful enough for more complex syntactic structures. • Regular expressions can describe regular languages, BNF can describe context-free languages.

12. Conventions for Writing Regular Expressions Figure 2.6

13. Next time… Syntactic Analysis