UP Lecture 14

Compilers
Parser
(202503)

Transcript

1. jgs Compilers Lecture 14: Parser Dr. Javier Gonzalez-Sanchez jgonzalezs@up.edu.mx
2. jgs Previously …
3. Dr. Javier Gonzalez-Sanchez | Compilers | 3 jgs Question {"name":false}
4. Dr. Javier Gonzalez-Sanchez | Compilers | 4 jgs Question {"name":false, "age" :100 }
5. Dr. Javier Gonzalez-Sanchez | Compilers | 5 jgs Question {"name":false, "age" :100, "grades”:[1,2,3] }
6. Dr. Javier Gonzalez-Sanchez | Compilers | 6 jgs Question {"name":false, "age" :100, "grades":{ "labs":[1,2,3] } }
7. Dr. Javier Gonzalez-Sanchez | Compilers | 7 jgs Let’s Work
8. Dr. Javier Gonzalez-Sanchez | Compilers | 8 jgs Rules PROGRAM BODY C EXPRESSION X Y R E A B { 0; 1 + 2; 3 * (4 + hello); }
9. Dr. Javier Gonzalez-Sanchez | Compilers | 9 jgs Rules PROGRAM BODY C A B { 0; 1 + 2; 3 * (4 + hello); } EXPRESSION X Y R E
10. Dr. Javier Gonzalez-Sanchez | Compilers | 10 jgs Let’s Work
11. jgs Parser
12. Dr. Javier Gonzalez-Sanchez | Compilers | 12 jgs Parser BNF EBNF A | AA & B ! Parser Grammar
13. Dr. Javier Gonzalez-Sanchez | Compilers | 13 jgs PREDICTIVE DESCENDENT RECURSIVE PARSER
14. Dr. Javier Gonzalez-Sanchez | Compilers | 14 jgs Parser | Step by Step For each rule in the grammar { ▪ Step 1. The left-hand side (method declaration) ▪ Step 2. The right-hand side (body of the method) as follows: ▪ Step 2.1 Non-terminals (boxes) will be a call to a method ▪ Step 2.2. Terminals (ovals) will be if-conditions ▪ Step 2.3. Lines in a loop (EBNF items) will be loops }
15. Dr. Javier Gonzalez-Sanchez | Compilers | 15 jgs Parser public class Parser { private static Vector<Token> tokens; private static int currentToken; public static void RULE_PROGRAM () {} public static void RULE_BODY () {} public static void RULE_EXPRESSION () {} public static void RULE_X () {} public static void RULE_Y () {} public static void RULE_R () {} public static void RULE_E () {} public static void RULE_A () {} public static void RULE_B () {} public static void RULE_C () {}
16. Dr. Javier Gonzalez-Sanchez | Compilers | 16 jgs Parser public static void RULE_PROGRAM() { if (tokens.get(currentToken).getWord().equals(“{”)) { currentToken++; else error(1); RULE_BODY(); if (tokens.get(currentToken).getWord().equals(“}”)) currentToken++; else error(2); } PROGRAM
17. Dr. Javier Gonzalez-Sanchez | Compilers | 17 jgs Parser public static void RULE_BODY() { while (!tokens.get(currentToken).getWord().equals(“}”)) { RULE_EXPRESSION(); if (tokens.get(currentToken).getWord().equals(“;”)) currentToken++; else error(3); } } BODY
18. Dr. Javier Gonzalez-Sanchez | Compilers | 18 jgs Parser public static void RULE_EXPRESSION() { RULE_X(); while (tokens.get(currentToken).getWord().equals(“|”)) { currentToken++; RULE_X(); } } EXPRESSION
19. Dr. Javier Gonzalez-Sanchez | Compilers | 19 jgs Parser public static void RULE_X() { RULE_Y(); while (tokens.get(currentToken).getWord().equals(“&”)) { currentToken++; RULE_Y(); } } X
20. Dr. Javier Gonzalez-Sanchez | Compilers | 20 jgs Parser public static void RULE_Y() { if (tokens.get(currentToken).getWord().equals(“!”)) { currentToken++; } RULE_R(); } Y
21. Dr. Javier Gonzalez-Sanchez | Compilers | 21 jgs Parser public static void RULE_R() { RULE_E(); while ( tokens.get(currentToken).getWord().equals(“<”) |tokens.get(currentToken).getWord().equals(“>”) |tokens.get(currentToken).getWord().equals(“==”) |tokens.get(currentToken).getWord().equals(“!=”) ) { currentToken++; RULE_E(); } } R
22. Dr. Javier Gonzalez-Sanchez | Compilers | 22 jgs Parser public static void RULE_E() { RULE_A(); while (tokens.get(currentToken).getWord().equals(“-”) | tokens.get(currentToken).getWord().equals(“+”) ) { currentToken++; RULE_A(); } } E
23. Dr. Javier Gonzalez-Sanchez | Compilers | 23 jgs Parser public static void RULE_A() { RULE_B(); while (tokens.get(currentToken).getWord().equals(“/”) | tokens.get(currentToken).getWord().equals(“*”) ) { currentToken++; RULE_B(); } } A
24. Dr. Javier Gonzalez-Sanchez | Compilers | 24 jgs Parser public static void RULE_B() { if (tokens.get(currentToken).getWord().equals(“-”)) { currentToken++; } RULE_C(); } B
25. Dr. Javier Gonzalez-Sanchez | Compilers | 25 jgs Parser public static void RULE_C() { if (tokens.get(currentToken).getToken().equals(“integer”)) { currentToken++; } else if (tokens.get(currentToken).getToken().equals(“identifier”)) { currentToken++; } else if (tokens.get(currentToken).getWord().equals(“(”)) { currentToken++; RULE_EXPRESSION(); if (tokens.get(currentToken).getWord().equals(“)”)) { currentToken++; } else error(4); } } else { error (5); } } C
26. Dr. Javier Gonzalez-Sanchez | Compilers | 26 jgs Homework
27. Dr. Javier Gonzalez-Sanchez | Compilers | 27 jgs Questions
28. jgs Compilers Javier Gonzalez-Sanchez, Ph.D. jgonzalezs@up.edu.mx Spring 2025 Copyright. These slides can only be used as study material for the Compilers course at Universidad Panamericana. They cannot be distributed or used for another purpose.
29. jgs Compilers Javier Gonzalez-Sanchez, Ph.D. jgonzalezs@up.edu.mx Spring 2025 Copyright. These slides can only be used as study material for the Compilers course at Universidad Panamericana. They cannot be distributed or used for another purpose.