NUMBER          → DIGIT+ ( "." DIGIT+ )? ;
STRING          → '"' <any char except '"'>* '"' ;
IDENTIFIER      → ALPHA ( ALPHA | DIGIT )* ;
ALPHA           → 'a' ... 'z' | 'A' ... 'Z' | '_' ;
DIGIT           → '0' ... '9' ;

program         → declaration* EOF ;

declaration     → classDecl
                | funDecl
                | varDecl
                | statement ;
classDecl       → "class" IDENTIFIER ( "<" IDENTIFIER )?
                "{" function* "}" ;
funDecl         → "fun" function ;
function        → IDENTIFIER "(" parameters? ")" block ;
parameters      → IDENTIFIER ( "," IDENTIFIER )* ;
varDecl         → "var" IDENTIFIER ( "=" expression )? ";" ;

statement       → exprStmt
                | forStmt
                | ifStmt
                | printStmt
                | returnStmt
                | whileStmt
                | block ;
                
exprStmt        → expression ";" ;                    
forStmt         → "for" "(" ( varDecl | exprStmt | ";" )
                            expression? ";"
                            expression? ")" statement ;
ifStmt          → "if" "(" expression ")" statement ( "else" statement )? ;
printStmt       → "print" expression ";" ;
returnStmt      → "return" expression? ";" ;
whileStmt       → "while" "(" expression ")" statement ; 
block           → "{" declaration* "}" ;

expression      → assignment ;

assignment      → ( call "." )? IDENTIFIER "=" assignment
                | logic_or ;
                
logic_or        → logic_and ( "or" logic_and )* ;
logic_and       → equality ( "and" equality )* ;
equality        → comparison ( ( "!=" | "==" ) comparison )* ;
comparison      → addition ( ( ">" | ">=" | "<" | "<=" ) addition )* ;
addition        → multiplication ( ( "-" | "+" ) multiplication )* ;
multiplication  → unary ( ( "/" | "*" ) unary )* ;

unary           → ( "!" | "-" ) unary | call ;
call            → primary ( "(" arguments? ")" | "." IDENTIFIER )* ;
arguments       → expression ( "," expression )* ;
primary         → "true" | "false" | "nil" | "this"
                | NUMBER | STRING | IDENTIFIER | "(" expression ")"
                | "super" "." IDENTIFIER ;