UP Lecture 14 - Speaker Deck

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jgs Compilers Lecture 14: Parser Implementation Dr. Javier Gonzalez-Sanchez [email protected]

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Dr. Javier Gonzalez-Sanchez | Compilers | 2 jgs PREDICTIVE DESCENDENT RECURSIVE PARSER

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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 }

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Dr. Javier Gonzalez-Sanchez | Compilers | 4 jgs Rules { 0; 1 + 2; 3 * (4 + hello); }

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jgs Next Step

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Dr. Javier Gonzalez-Sanchez | Compilers | 6 jgs Homework Teams of Three Members

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Dr. Javier Gonzalez-Sanchez | Compilers | 7 jgs Homework Programming Assignment 2 Develop a Predictive Descendent Recursive Parser by coding a Grammar

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Dr. Javier Gonzalez-Sanchez | Compilers | 8 jgs Question

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Dr. Javier Gonzalez-Sanchez | Compilers | 9 jgs GitHub Classroom https://classroom.github.com/a/--tRWhKA

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jgs Code

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Dr. Javier Gonzalez-Sanchez | Compilers | 11 jgs Homework You Need a Lexer

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Dr. Javier Gonzalez-Sanchez | Compilers | 12 jgs You Need a Lexer Add Yours To the Repository (I recommend creating a package 'Lexer'

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Dr. Javier Gonzalez-Sanchez | Compilers | 13 jgs Another Option (Just In Case)

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Dr. Javier Gonzalez-Sanchez | Compilers | 14 jgs Class Token

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Dr. Javier Gonzalez-Sanchez | Compilers | 15 jgs Class Automata

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Dr. Javier Gonzalez-Sanchez | Compilers | 16 jgs Class Lexer

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Dr. Javier Gonzalez-Sanchez | Compilers | 17 jgs Class Main

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Dr. Javier Gonzalez-Sanchez | Compilers | 18 jgs Class Main

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Dr. Javier Gonzalez-Sanchez | Compilers | 19 jgs Class Parser

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jgs Example

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Dr. Javier Gonzalez-Sanchez | Compilers | 21 jgs Grammar

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Dr. Javier Gonzalez-Sanchez | Compilers | 22 jgs Input

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Dr. Javier Gonzalez-Sanchez | Compilers | 23 jgs Input → Lexer

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Dr. Javier Gonzalez-Sanchez | Compilers | 24 jgs Input → Lexer → Parser

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jgs Next

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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

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Dr. Javier Gonzalez-Sanchez | Compilers | 27 jgs Assignment 2 | Code PROGRAM

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Dr. Javier Gonzalez-Sanchez | Compilers | 28 jgs Assignment 2 | Code METHODS

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Dr. Javier Gonzalez-Sanchez | Compilers | 29 jgs Assignment 2 | Code BODY

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Dr. Javier Gonzalez-Sanchez | Compilers | 30 jgs Assignment 2 | Code PARAMS

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Dr. Javier Gonzalez-Sanchez | Compilers | 31 jgs Assignment 2 | Code public static void RULE_ASSIGNMENT() { } ASSIGNMENT

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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

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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

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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

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Dr. Javier Gonzalez-Sanchez | Compilers | 35 jgs Parser public static void RULE_Y() { if (tokens.get(currentToken).getWord().equals(“!”)) { currentToken++; } RULE_R(); } Y

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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

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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

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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

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Dr. Javier Gonzalez-Sanchez | Compilers | 39 jgs Parser public static void RULE_B() { if (tokens.get(currentToken).getWord().equals(“-”)) { currentToken++; } RULE_C(); } B

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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

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Dr. Javier Gonzalez-Sanchez | Compilers | 41 jgs Assignment 2 | Code public static void RULE_C() { } C

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Dr. Javier Gonzalez-Sanchez | Compilers | 42 jgs Assignment 2 | Code public static void RULE_VARIABLE() { } VARIABLE

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Dr. Javier Gonzalez-Sanchez | Compilers | 43 jgs Assignment 2 | Code public static void RULE_WHILE() { } WHILE

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Dr. Javier Gonzalez-Sanchez | Compilers | 44 jgs Assignment 2 | Code public static void RULE_IF() { } IF

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Dr. Javier Gonzalez-Sanchez | Compilers | 45 jgs Assignment 2 | Code public static void RULE_RETURN() { } RETURN

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Dr. Javier Gonzalez-Sanchez | Compilers | 46 jgs Assignment 2 | Code public static void RULE_CALL_METHOD () { } CALL_METHOD

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Dr. Javier Gonzalez-Sanchez | Compilers | 47 jgs Assignment 2 | Code public static void RULE_PARAM_VALUES () { } PARAM_VALUES

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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.

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Dr. Javier Gonzalez-Sanchez | Compilers | 49 jgs Questions

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jgs Compilers Javier Gonzalez-Sanchez, Ph.D. [email protected] 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.