Chapter 2-2 A Simple One-Pass Compiler

1. Chapter 2-2A Simple One-Pass Compiler

2. Syntax-directed translation • Syntax-directed definition  translation of a construct in terms of attributes associated with its syntactic components • Syntactic structure :: context-free grammar • Grammar symbol :: a set of attributes and with each production, a set of semantic rules for computing values of the attributes associated with the symbols appearing in the production • Translation  input-output mapping • Annotated parse tree  a parse tree showing the attribute values at each node

3. Synthesized Attributes • An attribute is said to be synthesized if its value at a parse-tree node is determinedfrom attribute values at the children of node • 예제 설명

4. Syntax-directed definition for infix to postfix translation.

5. Attribute values at nodes in a parse tree.

6. Depth first traversals • Robot positioning :: • seq  seq instr | begin instr  east | north | west | south • Depth-first traversals • Translation Schemes • Context-free grammar in which program fragments called semantic actions are embedded • Emitting a Translation

7. Annotated parse tree for begin west south.

8. Syntax-directed definition of the robot’s position.

9. Actions translating expressions into postfix notation.

10. Actions translating 9-5+2 into 95-2+

11. Top-down parsing • Lookahead … the current token being scanned • Array[ num dotdot num ] of integer • 과정 설명

12. type simple |  id | array[ simple ]of type Simple  integer | char | num dotdot num (2.8)

13. (a) type type Array [ simple ] of type type (c) Array [ simple ] of type num dotdot num type (d) Array [ simple ] of type num dotdot num simple type (e) Array [ simple ] of type num dotdot num simple integer Steps in the top-down construction of a parse tree

14. Predictive parsing • First • 예제로 설명 • ∈-production • Designing a Predictive Parser • Left Recursion • expr  expr + term • 일반화

15. expr  term rest rest  + term { print(‘+’) } rest | - term { print(‘-’) } rest | term  0 { print (‘0’) } term  1 { print (‘1’) } . . . term  9 { print (‘9’) } (2.14)

16. Translation of 9 – 5 + 2 into 95 – 2 +. expr term rest 9 {print(‘9’)} - term {print(‘-’)} rest 5 {print(‘5’)} + term {print(‘+’)} rest 2 {print(‘2’)}

17. expr() { term(); rest(); } rest() { if(lookahead == ‘+’) { match(‘+’); term(); putchar(‘+’); rest(); } else if (lookahead == ‘-’) { match(‘-’); term(); putchar(‘-’); rest(); } else; } term() { if (isdigit(lookahead)) { putchar(lookahead); match(lookahead); } else error; } Fig. 2. 22. Functions for the nonterminals expr, rest, and term.

18. Replacement for functions expr and rest of Fig. 2.22. expr() { term(); while(1) if(lookahead == ‘+’) { match(‘+’); term(); putchar(‘+’); } else if (lookahead == ‘-’) { match(‘-’); term(); putchar(‘-’); } else break; }

19. Implementing the interactions in Fig. 2. 25. lexan() lexical analyzer uses getchar() return token to read character to caller pushes back c using ungetc(c, stdin) sets global variable to attribute value tokenval

20. Symbol table and array for storing strings.

21. stmt ifexprthenstmt1 { out := newlable; stmt.t := expr.t || ‘gofalse’ out || stmt1.t || ‘label’ out (2.18) WHILE IF Code layout for conditional and while statements.

22. Fig. 4.15. Parsing table M for grammar (4.11)