1. The College of Saint Rose CIS 433 – Programming Languages David Goldschmidt, Ph.D. from Concepts of Programming Languages, 9th edition by Robert W. Sebesta, Addison-Wesley, 2010, ISBN 0-13-607347-6

2. lexical analysis groups characters into lexical units syntax analysis transforms lexical units into parse trees a parse tree represents the syntactic structure of the program analyzes parse trees to produce intermediate code transforms intermediate code into executable machine code

3.  Syntax of an assignment statement in BNF:  BNF rule or production defining :  = ; abstraction being defined definition of  The definition consists of other abstractions, as well as lexemes and tokens

4.  begin end  | ;  =  a | b | c | d | e  + | -  | literal-integer-value a vertical bar indicates an OR a token, which is simply a grouping of lexemes  Write a sentence that conforms to this grammar

5.  A derivation is a repeated application of rules  Start with a start symbol and end with a sentence => begin end => begin = end => begin b = end => begin b = + end => begin b = c + end => begin b = c + 123 end  Many possible (often infinite) derivations  begin end  | ;  =  a | b | c | d | e  + | -  | literal-integer-value

6.  A parse tree represents the structure of a derivation  Every internal node is a non-terminal abstraction  Every leaf node is a terminal symbol  Draw a parse tree for ▪ B = A * C + D  =  A | B | C | D  + | * | ( ) | = = * * C C B B A A

7. = = * * B B A A + + C C D D  =  A | B | C | D  + | * | ( ) | B = A * C + D

8. = = + + B B * * A A C C D D  =  A | B | C | D  + | * | ( ) |

9.  A grammar that generates a sentential form for which there are two or more distinct parse trees is an ambiguous grammar  Ambiguity in a grammar leads to problems... ...because compilers often base semantics on parse trees ▪ operator precedence ▪ if-else parse trees are analyzed to produce intermediate code

10. Ambiguous grammar Unambiguous grammar  =  A | B | C | D  + | * | ( ) |  =  A | B | C | D  + |  * |  ( ) |  An unambiguous grammar has exactly one derivation and parse tree for each unique sentential form

11.  Read and study Chapter 3  Do Exercises at the end of Chapter 3  Do the What next? exercises from the Week 3 lecture notes  DUE NEXT CLASS!