C H A P T E R T W O

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

2. Syntactic Analysis: • Lexical Analysis  Token Stream • Remove comments and white space • Classify tokens by type • Token Stream  Syntactic Analysis • Define the structure of the elements of a program: • Expressions • Assignments • Loops, conditionals and other blocks. • The whole enchilada • Detect errors • Create a parse

3. A Concrete Syntax for Assignments and Expressions Figure 2.7 Note that Expressions can be recursively defined Expression and Term establish precedence for operators

4. Parse Tree for the Expression x+2*y Figure 2.8 Traversing the parse tree in an in-order sequence defines the order of evaluation. An Expression in parentheses becomes a Factor, changing the order of evaluation.

5. Sketch of a Parse Tree for a Complete Program Figure 2.9

6. Ambiguity: A grammar is ambiguous if it permits a string to be parsed into two or more different parse trees. AmbExp  Integer | AmbExp – AmbExp Consider the program fragment 2 – 3 – 4

7. Two Different Parse Trees for the AmbExp 2 – 3 – 4 Figure 2.10 (2 – 3) - 4 2 – (3 – 4)

8. An Ambiguous If Statement Figure 2.11 if (x<0) if (y<0) y = y – 1; else y = 0;

9. The “Dangling Else” Grammatical Ambiguity Figure 2.12

10. Extended BNF: EBNF simplifies the specification of recursion in grammar rules. Expression  Term | Expression + Term | Expression – Term Term  Factor | Term * Factor | Term / Factor Expression  Term { [ + | - ] Term } * Term  Factor { [‘*’ | / ] Factor } *

11. EBNF-Based Parse Tree for the Expression x+2*y Figure 2.13

12. Extended BNF: EBNF adds optional symbols on the right hand side of rules. Conditional  if ( Expression ) Statement { else Statement } opt

13. Next time… Linking Syntax And Semantics