MyLanguageV1Code.g4

// A simple syntax-directed translator for a simple language

grammar MyLanguageV1Code;

// Root non-terminal symbol
// A program is a bunch of declarations followed by a bunch of statements
// The Java code outputs the necessary NASM code around these declarations

program       :
              {System.out.println("%include \"asm_io.inc\"");
               System.out.println("segment .data"); }
              declaration*
              {System.out.println("segment .text");
               System.out.println("\tglobal asm_main");
               System.out.println("asm_main:");
               System.out.println("\tenter 0,0");
               System.out.println("\tpusha"); }
              statement*
              {System.out.println("\tpopa");
               System.out.println("\tmov eax,0");
               System.out.println("\tleave");
               System.out.println("\tret"); }
              ;

// Parse rule for variable declarations

declaration   :
              {int a,b; }
              INT a=NAME ASSIGN b=INTEGER SEMICOLON
              {System.out.println("\t"+$a.text + "  dd " + $b.text);}
              ;

// Parse rule for statements

statement      :
               ifstmt
             | dostmt
             | printstmt
             | aprintstmt
             | assignstmt
               ;

// Parse rule for do-while statements
dostmt      :
            DO
            {
              System.out.println("loop:");
            }
            statement*
            WHILE LPAREN a=identifier NOTEQUAL b=integer RPAREN
            {
              System.out.println("\tcmp dword "+$a.toString+","+$b.toString);
              System.out.println("\tjne loop");
            }
            ;

// Parse rule for if statements
ifstmt      :
            {int a,b;}
            {String label;}
            IF LPAREN a=identifier EQUAL b=integer RPAREN
            {System.out.println("tcmp dword "+$a.toString+","+$b.toString);
             label = "label_"+Integer.toString($IF.index);
             System.out.println("tjnz "+label); }
            statement*
            { System.out.println(label+":"); }
            ENDIF
            ;

// Parse rule for print statements
printstmt      :
               PRINT term SEMICOLON
               {System.out.println("\tmov eax, "+$term.toString);
                System.out.println("\tcall print_int");
                System.out.println("\tcall print_nl");}
               ;

aprintstmt     :
                PRINT term COMMA
                {System.out.println("\tmov eax, "+$term.toString);
                System.out.println("\tcall print_int");
                System.out.println("\tcall print_nl");}
              |
                term COMMA
                {System.out.println("\tmov eax, "+$term.toString);
                System.out.println("\tcall print_int");
                System.out.println("\tcall print_nl");}
              |
                term SEMICOLON
                {System.out.println("\tmov eax, "+$term.toString);
                 System.out.println("\tcall print_int");
                 System.out.println("\tcall print_nl");}
                ;

// Parse rule for assignment statements
assignstmt      :
                {int a; }
                a=NAME ASSIGN expression SEMICOLON
                {System.out.println("\tmov ["+$a.text+"], eax");}
                ;

// Parse rule for expressions
expression      :
                {int a,b; }
                a=term
                {System.out.println("\tmov eax,"+$a.toString);}
              |
                a=term PLUS b=term
                {System.out.println("\tmov eax,"+$a.toString);}
                {System.out.println("\tadd eax,"+$b.toString);}
              |
                a=term MINUS b=term
                {System.out.println("\tmov eax,"+$a.toString);}
                {System.out.println("\tsub eax,"+$b.toString);}
                ;

// Parse rule for terms
term returns [String toString]  :
                                identifier {$toString = $identifier.toString;}
                              | integer {$toString = $integer.toString;}
                                ;

// Parse rule for identifiers
identifier returns [String toString]: NAME {$toString = "["+$NAME.text+"]";} ;

// Parse rule for numbers
integer returns [String toString]: INTEGER {$toString = $INTEGER.text;} ;

// Reserved Keywords
////////////////////////////////
IF: 'if';
ENDIF: 'endif';
PRINT: 'print';
INT: 'int';
DO: 'do';
WHILE: 'while';

// Operators
PLUS: '+';
MINUS: '-';
EQUAL: '==';
ASSIGN: '=';
NOTEQUAL: '!=';

// Semicolon and parentheses
SEMICOLON: ';';
LPAREN: '(';
RPAREN: ')';
COMMA: ',';

// Integers
INTEGER: [0-9][0-9]*;

// Variable names
NAME: [a-z]+;

// Ignore all white spaces
WS: [ \t\r\n]+ -> skip ;