use super::chunk::{self, Chunk}; use super::errors::{Error, ErrorKind, LoxResult}; use super::opcode::OpCode; use super::value::Value; use crate::scanner::{self, Token, TokenKind}; struct Compiler<T: Iterator<Item = Token>> { tokens: T, chunk: Chunk, panic: bool, errors: Vec<Error>, // TODO(tazjin): Restructure so that these don't need to be Option? current: Option<Token>, previous: Option<Token>, } #[derive(Debug, PartialEq, PartialOrd)] enum Precedence { None, Assignment, // = Or, // or And, // and Equality, // == != Comparison, // < > <= >= Term, // + - Factor, // * / Unary, // ! - Call, // . () Primary, } type ParseFn<T> = fn(&mut Compiler<T>) -> LoxResult<()>; struct ParseRule<T: Iterator<Item = Token>> { prefix: Option<ParseFn<T>>, infix: Option<ParseFn<T>>, precedence: Precedence, } impl<T: Iterator<Item = Token>> ParseRule<T> { fn new( prefix: Option<ParseFn<T>>, infix: Option<ParseFn<T>>, precedence: Precedence, ) -> Self { ParseRule { prefix, infix, precedence, } } } impl Precedence { // Return the next highest precedence, if there is one. fn next(&self) -> Self { match self { Precedence::None => Precedence::Assignment, Precedence::Assignment => Precedence::Or, Precedence::Or => Precedence::And, Precedence::And => Precedence::Equality, Precedence::Equality => Precedence::Comparison, Precedence::Comparison => Precedence::Term, Precedence::Term => Precedence::Factor, Precedence::Factor => Precedence::Unary, Precedence::Unary => Precedence::Call, Precedence::Call => Precedence::Primary, Precedence::Primary => panic!( "invalid parser state: no higher precedence than Primary" ), } } } fn rule_for<T: Iterator<Item = Token>>(token: &TokenKind) -> ParseRule<T> { match token { TokenKind::LeftParen => { ParseRule::new(Some(Compiler::grouping), None, Precedence::None) } TokenKind::Minus => ParseRule::new( Some(Compiler::unary), Some(Compiler::binary), Precedence::Term, ), TokenKind::Plus => { ParseRule::new(None, Some(Compiler::binary), Precedence::Term) } TokenKind::Slash => { ParseRule::new(None, Some(Compiler::binary), Precedence::Factor) } TokenKind::Star => { ParseRule::new(None, Some(Compiler::binary), Precedence::Factor) } TokenKind::Number(_) => { ParseRule::new(Some(Compiler::number), None, Precedence::None) } _ => ParseRule::new(None, None, Precedence::None), } } impl<T: Iterator<Item = Token>> Compiler<T> { fn compile(&mut self) -> LoxResult<()> { self.advance(); self.expression()?; self.consume( &TokenKind::Eof, ErrorKind::ExpectedToken("Expected end of expression"), ); self.end_compiler() } fn advance(&mut self) { self.previous = self.current.take(); self.current = self.tokens.next(); } fn expression(&mut self) -> LoxResult<()> { self.parse_precedence(Precedence::Assignment) } fn number(&mut self) -> LoxResult<()> { if let TokenKind::Number(num) = self.previous().kind { self.emit_constant(num); return Ok(()); } unreachable!("internal parser error: entered number() incorrectly") } fn grouping(&mut self) -> LoxResult<()> { self.expression()?; self.consume( &TokenKind::RightParen, ErrorKind::ExpectedToken("Expected ')' after expression"), ); Ok(()) } fn unary(&mut self) -> LoxResult<()> { // TODO(tazjin): Avoid clone let kind = self.previous().kind.clone(); // Compile the operand self.parse_precedence(Precedence::Unary)?; // Emit operator instruction match kind { TokenKind::Minus => self.emit_op(OpCode::OpNegate), _ => unreachable!("only called for unary operator tokens"), } Ok(()) } fn binary(&mut self) -> LoxResult<()> { // Remember the operator let operator = self.previous().kind.clone(); // Compile the right operand let rule: ParseRule<T> = rule_for(&operator); self.parse_precedence(rule.precedence.next())?; // Emit operator instruction match operator { TokenKind::Minus => self.emit_op(OpCode::OpSubtract), TokenKind::Plus => self.emit_op(OpCode::OpAdd), TokenKind::Star => self.emit_op(OpCode::OpMultiply), TokenKind::Slash => self.emit_op(OpCode::OpDivide), _ => unreachable!("only called for binary operator tokens"), } Ok(()) } fn parse_precedence(&mut self, precedence: Precedence) -> LoxResult<()> { self.advance(); let rule: ParseRule<T> = rule_for(&self.previous().kind); let prefix_fn = match rule.prefix { None => unimplemented!("expected expression or something, unclear"), Some(func) => func, }; prefix_fn(self)?; while precedence <= rule_for::<T>(&self.current().kind).precedence { self.advance(); match rule_for::<T>(&self.previous().kind).infix { Some(func) => { func(self)?; } None => { unreachable!("invalid compiler state: error in parse rules") } } } Ok(()) } fn consume(&mut self, expected: &TokenKind, err: ErrorKind) { if (self.current().kind == *expected) { self.advance(); return; } self.error_at(self.current().line, err); } fn current_chunk(&mut self) -> &mut Chunk { &mut self.chunk } fn end_compiler(&mut self) -> LoxResult<()> { self.emit_op(OpCode::OpReturn); #[cfg(feature = "disassemble")] { chunk::disassemble_chunk(&self.chunk); println!("== compilation finished =="); } Ok(()) } fn emit_op(&mut self, op: OpCode) { let line = self.previous().line; self.current_chunk().add_op(op, line); } fn emit_constant(&mut self, val: Value) { let idx = self.chunk.add_constant(val); self.emit_op(OpCode::OpConstant(idx)); } fn previous(&self) -> &Token { self.previous .as_ref() .expect("invalid internal compiler state: missing previous token") } fn current(&self) -> &Token { self.current .as_ref() .expect("invalid internal compiler state: missing current token") } fn error_at(&mut self, line: usize, kind: ErrorKind) { if self.panic { return; } self.panic = true; self.errors.push(Error { kind, line }) } } pub fn compile(code: &str) -> Result<Chunk, Vec<Error>> { let chars = code.chars().collect::<Vec<char>>(); let tokens = scanner::scan(&chars).map_err(|errors| { errors.into_iter().map(Into::into).collect::<Vec<Error>>() })?; let mut compiler = Compiler { tokens: tokens.into_iter().peekable(), chunk: Default::default(), panic: false, errors: vec![], current: None, previous: None, }; compiler.compile()?; if compiler.errors.is_empty() { Ok(compiler.chunk) } else { Err(compiler.errors) } }