ternary.y

%{
  #include <stdio.h>
  #include <stdlib.h>
  int yylex();
  int yyerror();

/*
This yacc program defines Grammar for ternary operator of C language,
to generate the parser for the same.
Parser created by lex is a LALR parser.

* TERNARY OPERATOR
        ternary operator takes 3 argumen
        1. The first is a comparison argument 
        2. The second is the result upon a true comparision.
        3. the third is the result upon false comparision.

* The program will check the given input is vaild or not based on the grammar rules defined.

INPUT : Nested or not nested expression on ternary operator.

OUTPUT :  Displays 'input accepted' for a vaild input.
          otherwise, displays 'Expression is not vaild' for invaild input.

Names of symbols in the parser that are tokens:

NUM :           for any numeric value
ID  :           for any variable.
NEWLINE :       for newline character.
LE :            for less than equal to "<=".
GE :            for greater than equal to ">=".
EQ :            for equals to "==".
NE :            for not equals "!="
OR :            for logical OR '||'
AND             for logical AND '&&''


GRAMMAR RULES:

        smallest string accepted by the language generated by the grammar
        is : statement ? statement : statement
        Assumption : the parser only accept boolean , logical and comparission statements.
*/

%}


%token NUM ID NEWLINE LE GE EQ NE OR AND T F NOT
%right '?' ':'
%left OR 
%left AND
%left EQ NE
%left LE GE  '<' '>'
%right NOT 
%left '(' ')'
%%

ST      :
        |ST S NEWLINE {printf("Input accepted.\n");}  
        ;


S       :EXP S1
        |'(' S ')'
        |'(' S ')' S1
        ;

S1      :'?' S2
        ;

S2      :EXP S3
        |S S3
        ;

S3      :':' S4
        ;
        
S4      :EXP 
        |S
        ;

EXP     : EXP'<'EXP  
        | EXP'>'EXP  
        | EXP LE EXP 
        | EXP GE EXP 
        | EXP EQ EXP 
        | EXP NE EXP 
        | EXP OR EXP 
        | EXP AND EXP
        | NOT EXP
        |ID
        |NUM        
        |'(' EXP ')'
        |T
        |F
        ;

%%

int main() {
    printf("Enter expression: \n");
    yyparse();
    return 0;
}
 
int yyerror(char* s) {
    printf("Expression is not valid\n");
}