%{

#include <stdio.h>

int yydebug=1;

int yylex(void);

int i;

#define border printf("\n"); for(i=0; i<=80; ++i) { putchar('-'); } printf("\n");

int yyerror(char *errorMsg);

void success(char *successMsg);

%}

// tokens

%token ID NUMBER STRING_LIT STRING_VAR

%token EQ PLUS MINUS MUL DIVIDE LBRACKET RBRACKET SEMICOLON

%token PRINT KEYWORD

// set precedence

%right EQ

%left PLUS MINUS

%left MUL DIVIDE

%%

/* Parser Grammar */

start: stmt SEMICOLON {

success("This is a valid python expression");

YYACCEPT;

}

;

stmt: assign_arithmetic

| assign_str

| display

;

identifier: ID | keyword {

yyerror("\nkeyword can't be used as a identifier\n");

YYABORT;

}

;

keyword: PRINT | KEYWORD

;

assign_str: identifier EQ strings

;

display: PRINT strings

| PRINT strings MUL NUMBER

| PRINT strings PLUS strings

| PRINT expr

;

strings: STRING_LIT | STRING_VAR

;

assign_arithmetic: identifier EQ expr

;

expr: expr PLUS expr

| expr MINUS expr

| expr MUL expr

| expr DIVIDE expr

| factor

| LBRACKET expr RBRACKET

| SIGN factor

;

SIGN: PLUS

| MINUS

;

factor: identifier

| NUMBER

;

%%