jLox

jLox is an interpreter for the Lox programming language written in Java.

Lox Syntax Grammar

program → declaration* EOF ;

Declarations

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

Statements

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* "}" ;

Expressions

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 )* ;
primary → "true" | "false" | "nil" | "this" | NUMBER | STRING | IDENTIFIER | "(" expression ")" | "super" "." IDENTIFIER ;

Utility Rules

function → IDENTIFIER "(" parameters? ")" block ;
parameters → IDENTIFIER ( "," IDENTIFIER )* ;
arguments → expression ( "," expression )* ;

Lexical Grammar

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