UP Lecture 14

Compilers
Parser Implementation
(202603)

Transcript

1. jgs Compilers Lecture 14: Parser Implementation Dr. Javier Gonzalez-Sanchez jgonzalezs@up.edu.mx
2. Dr. Javier Gonzalez-Sanchez | Compilers | 2 jgs PREDICTIVE DESCENDENT RECURSIVE PARSER
3. Dr. Javier Gonzalez-Sanchez | Compilers | 3 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 }
4. Dr. Javier Gonzalez-Sanchez | Compilers | 4 jgs Rules { 0; 1 + 2; 3 * (4 + hello); }
5. jgs Next Step
6. Dr. Javier Gonzalez-Sanchez | Compilers | 6 jgs Homework Teams of Three Members
7. Dr. Javier Gonzalez-Sanchez | Compilers | 7 jgs Homework Programming Assignment 2 Develop a Predictive Descendent Recursive Parser by coding a Grammar
8. Dr. Javier Gonzalez-Sanchez | Compilers | 8 jgs Question
9. Dr. Javier Gonzalez-Sanchez | Compilers | 9 jgs GitHub Classroom https://classroom.github.com/a/--tRWhKA
10. jgs Code
11. Dr. Javier Gonzalez-Sanchez | Compilers | 11 jgs Homework You Need a Lexer
12. Dr. Javier Gonzalez-Sanchez | Compilers | 12 jgs You Need a Lexer Add Yours To the Repository (I recommend creating a package 'Lexer'
13. Dr. Javier Gonzalez-Sanchez | Compilers | 13 jgs Another Option (Just In Case)
14. Dr. Javier Gonzalez-Sanchez | Compilers | 14 jgs Class Token
15. Dr. Javier Gonzalez-Sanchez | Compilers | 15 jgs Class Automata
16. Dr. Javier Gonzalez-Sanchez | Compilers | 16 jgs Class Lexer
17. Dr. Javier Gonzalez-Sanchez | Compilers | 17 jgs Class Main
18. Dr. Javier Gonzalez-Sanchez | Compilers | 18 jgs Class Main
19. Dr. Javier Gonzalez-Sanchez | Compilers | 19 jgs Class Parser
20. jgs Example
21. Dr. Javier Gonzalez-Sanchez | Compilers | 21 jgs Grammar
22. Dr. Javier Gonzalez-Sanchez | Compilers | 22 jgs Input
23. Dr. Javier Gonzalez-Sanchez | Compilers | 23 jgs Input → Lexer
24. Dr. Javier Gonzalez-Sanchez | Compilers | 24 jgs Input → Lexer → Parser
25. jgs Next
26. Dr. Javier Gonzalez-Sanchez | Compilers | 26 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
27. Dr. Javier Gonzalez-Sanchez | Compilers | 27 jgs Assignment 2 | Code PROGRAM
28. Dr. Javier Gonzalez-Sanchez | Compilers | 28 jgs Assignment 2 | Code METHODS
29. Dr. Javier Gonzalez-Sanchez | Compilers | 29 jgs Assignment 2 | Code BODY
30. Dr. Javier Gonzalez-Sanchez | Compilers | 30 jgs Assignment 2 | Code PARAMS
31. Dr. Javier Gonzalez-Sanchez | Compilers | 31 jgs Assignment 2 | Code public static void RULE_ASSIGNMENT() { } ASSIGNMENT
32. Dr. Javier Gonzalez-Sanchez | Compilers | 32 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
33. Dr. Javier Gonzalez-Sanchez | Compilers | 33 jgs Parser public static void RULE_EXPRESSION() { RULE_X(); while (tokens.get(currentToken).getWord().equals(“|”)) { currentToken++; RULE_X(); } } EXPRESSION
34. Dr. Javier Gonzalez-Sanchez | Compilers | 34 jgs Parser public static void RULE_X() { RULE_Y(); while (tokens.get(currentToken).getWord().equals(“&”)) { currentToken++; RULE_Y(); } } X
35. Dr. Javier Gonzalez-Sanchez | Compilers | 35 jgs Parser public static void RULE_Y() { if (tokens.get(currentToken).getWord().equals(“!”)) { currentToken++; } RULE_R(); } Y
36. Dr. Javier Gonzalez-Sanchez | Compilers | 36 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
37. Dr. Javier Gonzalez-Sanchez | Compilers | 37 jgs Parser public static void RULE_E() { RULE_A(); while (tokens.get(currentToken).getWord().equals(“-”) | tokens.get(currentToken).getWord().equals(“+”) ) { currentToken++; RULE_A(); } } E
38. Dr. Javier Gonzalez-Sanchez | Compilers | 38 jgs Parser public static void RULE_A() { RULE_B(); while (tokens.get(currentToken).getWord().equals(“/”) | tokens.get(currentToken).getWord().equals(“*”) ) { currentToken++; RULE_B(); } } A
39. Dr. Javier Gonzalez-Sanchez | Compilers | 39 jgs Parser public static void RULE_B() { if (tokens.get(currentToken).getWord().equals(“-”)) { currentToken++; } RULE_C(); } B
40. Dr. Javier Gonzalez-Sanchez | Compilers | 40 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
41. Dr. Javier Gonzalez-Sanchez | Compilers | 41 jgs Assignment 2 | Code public static void RULE_C() { } C
42. Dr. Javier Gonzalez-Sanchez | Compilers | 42 jgs Assignment 2 | Code public static void RULE_VARIABLE() { } VARIABLE
43. Dr. Javier Gonzalez-Sanchez | Compilers | 43 jgs Assignment 2 | Code public static void RULE_WHILE() { } WHILE
44. Dr. Javier Gonzalez-Sanchez | Compilers | 44 jgs Assignment 2 | Code public static void RULE_IF() { } IF
45. Dr. Javier Gonzalez-Sanchez | Compilers | 45 jgs Assignment 2 | Code public static void RULE_RETURN() { } RETURN
46. Dr. Javier Gonzalez-Sanchez | Compilers | 46 jgs Assignment 2 | Code public static void RULE_CALL_METHOD () { } CALL_METHOD
47. Dr. Javier Gonzalez-Sanchez | Compilers | 47 jgs Assignment 2 | Code public static void RULE_PARAM_VALUES () { } PARAM_VALUES
48. Dr. Javier Gonzalez-Sanchez | Compilers | 48 jgs Homework The first version of your parser (without error handling) is due in one week. Focus on implementing the grammar rules and parsing functionality. Assume the input is always correct; if an error occurs, the parser may stop.
49. Dr. Javier Gonzalez-Sanchez | Compilers | 49 jgs Questions
50. 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.