Assignment-3/parser.y

%{
#include <iostream>
#include <set>

#include "parser.hpp"

extern int yylex();
void yyerror(YYLTYPE* loc, const char* err);
std::string* translate_boolean_str(std::string* boolean_str);

/*
 * Here, target_program is a string that will hold the target program being
 * generated, and symbols is a simple symbol table.
 */
std::string* target_program;
std::set<std::string> symbols;
%}

/* Enable location tracking. */
%locations

/*
 * All program constructs will be represented as strings, specifically as
 * their corresponding C/C++ translation.
 */
%define api.value.type { std::string* }

/*
 * Because the lexer can generate more than one token at a time (i.e. DEDENT
 * tokens), we'll use a push parser.
 */
%define api.pure full
%define api.push-pull push

/*
 * These are all of the terminals in our grammar, i.e. the syntactic
 * categories that can be recognized by the lexer.
 */
%token IDENTIFIER
%token FLOAT INTEGER BOOLEAN
%token INDENT DEDENT NEWLINE
%token AND BREAK DEF ELIF ELSE FOR IF NOT OR RETURN WHILE
%token ASSIGN PLUS MINUS TIMES DIVIDEDBY
%token EQ NEQ GT GTE LT LTE
%token LPAREN RPAREN COMMA COLON

/*
 * Here, we're defining the precedence of the operators.  The ones that appear
 * later have higher precedence.  All of the operators are left-associative
 * except the "not" operator, which is right-associative.
 */
%left OR
%left AND
%left PLUS MINUS
%left TIMES DIVIDEDBY
%left EQ NEQ GT GTE LT LTE
%right NOT

/* This is our goal/start symbol. */
%start program

%%

/*
 * Each of the CFG rules below recognizes a particular program construct in
 * Python and creates a new string containing the corresponding C/C++
 * translation.  Since we're allocating strings as we go, we also free them
 * as we no longer need them.  Specifically, each string is freed after it is
 * combined into a larger string.
 */
program
  : statements { target_program = $1; }
  ;

statements
  : statement { $$ = $1; }
  | statements statement { $$ = new std::string(*$1 + *$2); delete $1; delete $2; }
  ;

statement
  : assign_statement { $$ = $1; }
  | if_statement { $$ = $1; }
  | while_statement { $$ = $1; }
  | break_statement { $$ = $1; }
  ;

primary_expression
  : IDENTIFIER { $$ = $1; }
  | FLOAT { $$ = $1; }
  | INTEGER { $$ = $1; }
  | BOOLEAN { $$ = translate_boolean_str($1); delete $1; }
  | LPAREN expression RPAREN { $$ = new std::string("(" + *$2 + ")"); delete $2; }
  ;

negated_expression
  : NOT primary_expression { $$ = new std::string("!" + *$2); delete $2; }
  ;

expression
  : primary_expression { $$ = $1; }
  | negated_expression { $$ = $1; }
  | expression PLUS expression { $$ = new std::string(*$1 + " + " + *$3); delete $1; delete $3; }
  | expression MINUS expression { $$ = new std::string(*$1 + " - " + *$3); delete $1; delete $3; }
  | expression TIMES expression { $$ = new std::string(*$1 + " * " + *$3); delete $1; delete $3; }
  | expression DIVIDEDBY expression { $$ = new std::string(*$1 + " / " + *$3); delete $1; delete $3; }
  | expression EQ expression { $$ = new std::string(*$1 + " == " + *$3); delete $1; delete $3; }
  | expression NEQ expression { $$ = new std::string(*$1 + " != " + *$3); delete $1; delete $3; }
  | expression GT expression { $$ = new std::string(*$1 + " > " + *$3); delete $1; delete $3; }
  | expression GTE expression { $$ = new std::string(*$1 + " >= " + *$3); delete $1; delete $3; }
  | expression LT expression { $$ = new std::string(*$1 + " < " + *$3); delete $1; delete $3; }
  | expression LTE expression { $$ = new std::string(*$1 + " <= " + *$3); delete $1; delete $3; }
  ;

assign_statement
  : IDENTIFIER ASSIGN expression NEWLINE { symbols.insert(*$1); $$ = new std::string(*$1 + " = " + *$3 + ";\n"); delete $1; delete $3; }
  ;

block
  : INDENT statements DEDENT { $$ = new std::string("{\n" + *$2 + "}"); delete $2; }
  ;

condition
  : expression { $$ = $1; }
  | condition AND condition { $$ = new std::string(*$1 + " && " + *$3); delete $1; delete $3; }
  | condition OR condition { $$ = new std::string(*$1 + " || " + *$3); delete $1; delete $3; }
  ;

if_statement
  : IF condition COLON NEWLINE block elif_blocks else_block { $$ = new std::string("if (" + *$2 + ") " + *$5 + *$6 + *$7 + "\n"); delete $2; delete $5; delete $6; delete $7; }
  ;

elif_blocks
  : %empty { $$ = new std::string(""); }
  | elif_blocks ELIF condition COLON NEWLINE block { $$ = new std::string(*$1 + " else if (" + *$3 + ") " + *$6); delete $1; delete $3; delete $6; }
  ;

else_block
  : %empty { $$ = new std::string(""); }
  | ELSE COLON NEWLINE block { $$ = new std::string(" else " + *$4); delete $4; }


while_statement
  : WHILE condition COLON NEWLINE block { $$ = new std::string("while (" + *$2 + ") " + *$5 + "\n"); delete $2; delete $5; }
  ;

break_statement
  : BREAK NEWLINE { $$ = new std::string("break;\n"); }
  ;

%%

void yyerror(YYLTYPE* loc, const char* err) {
  std::cerr << "Error (line " << loc->first_line << "): " << err << std::endl;
}

/*
 * This function translates a Python boolean value into the corresponding
 * C++ boolean value.
 */
std::string* translate_boolean_str(std::string* boolean_str) {
  if (*boolean_str == "True") {
    return new std::string("true");
  } else {
    return new std::string("false");
  }
}