diff options
Diffstat (limited to 'users/tazjin/rlox/src/treewalk')
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/errors.rs | 38 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/interpreter.rs | 8 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/interpreter/builtins.rs | 4 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/mod.rs | 11 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/parser.rs | 702 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/resolver.rs | 6 | ||||
| -rw-r--r-- | users/tazjin/rlox/src/treewalk/scanner.rs | 283 |
7 files changed, 1042 insertions, 10 deletions
diff --git a/users/tazjin/rlox/src/treewalk/errors.rs b/users/tazjin/rlox/src/treewalk/errors.rs new file mode 100644 index 000000000000..3d5c28f9f3bb --- /dev/null +++ b/users/tazjin/rlox/src/treewalk/errors.rs @@ -0,0 +1,38 @@ +use crate::treewalk::interpreter::Value; + +#[derive(Debug)] +pub enum ErrorKind { + UnexpectedChar(char), + UnterminatedString, + UnmatchedParens, + ExpectedExpression(String), + ExpectedSemicolon, + ExpectedClosingBrace, + ExpectedToken(&'static str), + TypeError(String), + UndefinedVariable(String), + InternalError(String), + InvalidAssignmentTarget(String), + RuntimeError(String), + StaticError(String), + + // This variant is not an error, rather it is used for + // short-circuiting out of a function body that hits a `return` + // statement. + // + // It's implemented this way because in the original book the + // author uses exceptions for control flow, and this is the + // closest equivalent that I had available without diverging too + // much. + FunctionReturn(Value), +} + +#[derive(Debug)] +pub struct Error { + pub line: usize, + pub kind: ErrorKind, +} + +pub fn report(err: &Error) { + eprintln!("[line {}] Error: {:?}", err.line, err.kind); +} diff --git a/users/tazjin/rlox/src/treewalk/interpreter.rs b/users/tazjin/rlox/src/treewalk/interpreter.rs index 5b47dc0248f9..a096716d9155 100644 --- a/users/tazjin/rlox/src/treewalk/interpreter.rs +++ b/users/tazjin/rlox/src/treewalk/interpreter.rs @@ -1,7 +1,7 @@ -use crate::errors::{Error, ErrorKind}; -use crate::parser::{self, Block, Expr, Literal, Statement}; -use crate::scanner::{self, TokenKind}; -use crate::treewalk::resolver; +use crate::treewalk::errors::{Error, ErrorKind}; +use crate::treewalk::parser::{self, Block, Expr, Literal, Statement}; +use crate::treewalk::scanner::{self, TokenKind}; +use crate::treewalk::treewalk::resolver; use std::collections::HashMap; use std::rc::Rc; use std::sync::RwLock; diff --git a/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs b/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs index 0ec6ae08c354..709e53c7c0eb 100644 --- a/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs +++ b/users/tazjin/rlox/src/treewalk/interpreter/builtins.rs @@ -1,8 +1,8 @@ use std::fmt; use std::time::{SystemTime, UNIX_EPOCH}; -use crate::errors::Error; -use crate::parser::Literal; +use crate::treewalk::errors::Error; +use crate::treewalk::parser::Literal; use crate::treewalk::interpreter::Value; pub trait Builtin: fmt::Debug { diff --git a/users/tazjin/rlox/src/treewalk/mod.rs b/users/tazjin/rlox/src/treewalk/mod.rs index 95136b2fa141..ae1049a12eff 100644 --- a/users/tazjin/rlox/src/treewalk/mod.rs +++ b/users/tazjin/rlox/src/treewalk/mod.rs @@ -1,7 +1,10 @@ use crate::*; -pub mod interpreter; +mod errors; +mod parser; mod resolver; +mod scanner; +pub mod interpreter; pub fn main() { let mut args = env::args(); @@ -50,3 +53,9 @@ fn run(lox: &mut treewalk::interpreter::Interpreter, code: &str) { report_errors(errors); } } + +fn report_errors(errors: Vec<errors::Error>) { + for error in errors { + errors::report(&error); + } +} diff --git a/users/tazjin/rlox/src/treewalk/parser.rs b/users/tazjin/rlox/src/treewalk/parser.rs new file mode 100644 index 000000000000..8117c29726c9 --- /dev/null +++ b/users/tazjin/rlox/src/treewalk/parser.rs @@ -0,0 +1,702 @@ +// This implements the grammar of Lox as described starting in the +// Crafting Interpreters chapter "Representing Code". Note that the +// upstream Java implementation works around Java being bad at value +// classes by writing a code generator for Java. +// +// My Rust implementation skips this step because it's unnecessary, we +// have real types. +use crate::treewalk::errors::{Error, ErrorKind}; +use crate::treewalk::scanner::{Token, TokenKind}; +use std::rc::Rc; + +// AST + +#[derive(Debug)] +pub struct Assign { + pub name: Token, + pub value: Box<Expr>, + pub depth: Option<usize>, +} + +#[derive(Debug)] +pub struct Binary { + pub left: Box<Expr>, + pub operator: Token, + pub right: Box<Expr>, +} + +#[derive(Debug)] +pub struct Logical { + pub left: Box<Expr>, + pub operator: Token, + pub right: Box<Expr>, +} + +#[derive(Debug)] +pub struct Grouping(pub Box<Expr>); + +#[derive(Debug, Clone, PartialEq)] +pub enum Literal { + Boolean(bool), + Number(f64), + String(String), + Nil, +} + +#[derive(Debug)] +pub struct Unary { + pub operator: Token, + pub right: Box<Expr>, +} + +#[derive(Debug)] +pub struct Call { + pub callee: Box<Expr>, + pub paren: Token, + pub args: Vec<Expr>, +} + +// Not to be confused with `Var`, which is for assignment. +#[derive(Debug)] +pub struct Variable { + pub name: Token, + pub depth: Option<usize>, +} + +#[derive(Debug)] +pub enum Expr { + Assign(Assign), + Binary(Binary), + Grouping(Grouping), + Literal(Literal), + Unary(Unary), + Call(Call), + Variable(Variable), + Logical(Logical), +} + +// Variable assignment. Not to be confused with `Variable`, which is +// for access. +#[derive(Debug)] +pub struct Var { + pub name: Token, + pub initialiser: Option<Expr>, +} + +#[derive(Debug)] +pub struct Return { + pub value: Expr, +} + +#[derive(Debug)] +pub struct If { + pub condition: Expr, + pub then_branch: Box<Statement>, + pub else_branch: Option<Box<Statement>>, +} + +#[derive(Debug)] +pub struct While { + pub condition: Expr, + pub body: Box<Statement>, +} + +pub type Block = Vec<Statement>; + +#[derive(Debug)] +pub struct Function { + pub name: Token, + pub params: Vec<Token>, + pub body: Block, +} + +#[derive(Debug)] +pub enum Statement { + Expr(Expr), + Print(Expr), + Var(Var), + Block(Block), + If(If), + While(While), + Function(Rc<Function>), + Return(Return), +} + +// Parser + +/* +program → declaration* EOF ; + +declaration → funDecl + | varDecl + | statement ; + +funDecl → "fun" function ; +function → IDENTIFIER "(" parameters? ")" block ; +parameters → IDENTIFIER ( "," IDENTIFIER )* ; + + +statement → exprStmt + | forStmt + | ifStmt + | printStmt + | returnStmt + | whileStmt + | block ; + +forStmt → "for" "(" ( varDecl | exprStmt | ";" ) + expression? ";" + expression? ")" statement ; + +returnStmt → "return" expression? ";" ; + +whileStmt → "while" "(" expression ")" statement ; + +exprStmt → expression ";" ; + +ifStmt → "if" "(" expression ")" statement + ( "else" statement )? ; + +printStmt → "print" expression ";" ; + +expression → assignment ; +assignment → IDENTIFIER "=" assignment + | logic_or ; +logic_or → logic_and ( "or" logic_and )* ; +logic_and → equality ( "and" equality )* ; +equality → comparison ( ( "!=" | "==" ) comparison )* ; +comparison → term ( ( ">" | ">=" | "<" | "<=" ) term )* ; +term → factor ( ( "-" | "+" ) factor )* ; +factor → unary ( ( "/" | "*" ) unary )* ; +unary → ( "!" | "-" ) unary | call ; +call → primary ( "(" arguments? ")" )* ; +arguments → expression ( "," expression )* ; +primary → NUMBER | STRING | "true" | "false" | "nil" + | "(" expression ")" ; +*/ + +struct Parser { + tokens: Vec<Token>, + current: usize, +} + +type ExprResult = Result<Expr, Error>; +type StmtResult = Result<Statement, Error>; + +impl Parser { + // recursive-descent parser functions + + fn declaration(&mut self) -> StmtResult { + if self.match_token(&TokenKind::Fun) { + return self.function(); + } + + if self.match_token(&TokenKind::Var) { + return self.var_declaration(); + } + + self.statement() + } + + fn function(&mut self) -> StmtResult { + let name = self.identifier("Expected function name.")?; + + self.consume( + &TokenKind::LeftParen, + ErrorKind::ExpectedToken("Expect '(' after function name."), + )?; + + let mut params = vec![]; + + if !self.check_token(&TokenKind::RightParen) { + loop { + if params.len() >= 255 { + return Err(Error { + line: self.peek().line, + kind: ErrorKind::InternalError("255 parameter limit exceeded.".into()), + }); + } + + params.push(self.identifier("Expected parameter name.")?); + + if !self.match_token(&TokenKind::Comma) { + break; + } + } + } + + self.consume( + &TokenKind::RightParen, + ErrorKind::ExpectedToken("Expect ')' after parameters."), + )?; + + self.consume( + &TokenKind::LeftBrace, + ErrorKind::ExpectedToken("Expect '{' before function body."), + )?; + + Ok(Statement::Function(Rc::new(Function { + name, + params, + body: self.block_statement()?, + }))) + } + + fn var_declaration(&mut self) -> StmtResult { + // Since `TokenKind::Identifier` carries data, we can't use + // `consume`. + let mut var = Var { + name: self.identifier("Expected variable name.")?, + initialiser: None, + }; + + if self.match_token(&TokenKind::Equal) { + var.initialiser = Some(self.expression()?); + } + + self.consume(&TokenKind::Semicolon, ErrorKind::ExpectedSemicolon)?; + Ok(Statement::Var(var)) + } + + fn statement(&mut self) -> StmtResult { + if self.match_token(&TokenKind::Print) { + self.print_statement() + } else if self.match_token(&TokenKind::LeftBrace) { + Ok(Statement::Block(self.block_statement()?)) + } else if self.match_token(&TokenKind::If) { + self.if_statement() + } else if self.match_token(&TokenKind::While) { + self.while_statement() + } else if self.match_token(&TokenKind::For) { + self.for_statement() + } else if self.match_token(&TokenKind::Return) { + self.return_statement() + } else { + self.expr_statement() + } + } + + fn print_statement(&mut self) -> StmtResult { + let expr = self.expression()?; + self.consume(&TokenKind::Semicolon, ErrorKind::ExpectedSemicolon)?; + Ok(Statement::Print(expr)) + } + + fn block_statement(&mut self) -> Result<Block, Error> { + let mut block: Block = vec![]; + + while !self.check_token(&TokenKind::RightBrace) && !self.is_at_end() { + block.push(self.declaration()?); + } + + self.consume(&TokenKind::RightBrace, ErrorKind::ExpectedClosingBrace)?; + + Ok(block) + } + + fn if_statement(&mut self) -> StmtResult { + self.consume( + &TokenKind::LeftParen, + ErrorKind::ExpectedToken("Expected '(' after 'if'"), + )?; + let condition = self.expression()?; + self.consume( + &TokenKind::RightParen, + ErrorKind::ExpectedToken("Expected ')' after condition"), + )?; + + let then_branch = Box::new(self.statement()?); + + let mut stmt = If { + condition, + then_branch, + else_branch: Option::None, + }; + + if self.match_token(&TokenKind::Else) { + stmt.else_branch = Some(Box::new(self.statement()?)); + } + + Ok(Statement::If(stmt)) + } + + fn while_statement(&mut self) -> StmtResult { + self.consume( + &TokenKind::LeftParen, + ErrorKind::ExpectedToken("Expected '(' after 'while'"), + )?; + + let condition = self.expression()?; + + self.consume( + &TokenKind::RightParen, + ErrorKind::ExpectedToken("Expected ')' after 'while'"), + )?; + + Ok(Statement::While(While { + condition, + body: Box::new(self.statement()?), + })) + } + + fn for_statement(&mut self) -> StmtResult { + // Parsing of clauses ... + self.consume( + &TokenKind::LeftParen, + ErrorKind::ExpectedToken("Expected '(' after 'for'"), + )?; + + let initialiser = if self.match_token(&TokenKind::Semicolon) { + None + } else if self.match_token(&TokenKind::Var) { + Some(self.var_declaration()?) + } else { + Some(self.expr_statement()?) + }; + + let condition = if self.check_token(&TokenKind::Semicolon) { + // unspecified condition => infinite loop + Expr::Literal(Literal::Boolean(true)) + } else { + self.expression()? + }; + + self.consume(&TokenKind::Semicolon, ErrorKind::ExpectedSemicolon)?; + + let increment = if self.check_token(&TokenKind::RightParen) { + None + } else { + Some(self.expression()?) + }; + + self.consume( + &TokenKind::RightParen, + ErrorKind::ExpectedToken("Expected ')' after for clauses"), + )?; + + let mut body = self.statement()?; + + // ... desugaring to while + + if let Some(inc) = increment { + body = Statement::Block(vec![body, Statement::Expr(inc)]); + } + + body = Statement::While(While { + condition, + body: Box::new(body), + }); + + if let Some(init) = initialiser { + body = Statement::Block(vec![init, body]); + } + + Ok(body) + } + + fn return_statement(&mut self) -> StmtResult { + let value = self.expression()?; + self.consume(&TokenKind::Semicolon, ErrorKind::ExpectedSemicolon)?; + Ok(Statement::Return(Return { value })) + } + + fn expr_statement(&mut self) -> StmtResult { + let expr = self.expression()?; + self.consume(&TokenKind::Semicolon, ErrorKind::ExpectedSemicolon)?; + Ok(Statement::Expr(expr)) + } + + fn expression(&mut self) -> ExprResult { + self.assignment() + } + + fn assignment(&mut self) -> ExprResult { + let expr = self.logic_or()?; + + if self.match_token(&TokenKind::Equal) { + let equals = self.previous().clone(); + let value = self.assignment()?; + + if let Expr::Variable(Variable { name, .. }) = expr { + return Ok(Expr::Assign(Assign { + name, + value: Box::new(value), + depth: None, + })); + } + + return Err(Error { + line: equals.line, + kind: ErrorKind::InvalidAssignmentTarget(format!("{:?}", equals)), + }); + } + + Ok(expr) + } + + fn logic_or(&mut self) -> ExprResult { + let mut expr = self.logic_and()?; + + while self.match_token(&TokenKind::Or) { + expr = Expr::Logical(Logical { + left: Box::new(expr), + operator: self.previous().clone(), + right: Box::new(self.logic_and()?), + }) + } + + Ok(expr) + } + + fn logic_and(&mut self) -> ExprResult { + let mut expr = self.equality()?; + + while self.match_token(&TokenKind::And) { + expr = Expr::Logical(Logical { + left: Box::new(expr), + operator: self.previous().clone(), + right: Box::new(self.equality()?), + }) + } + + Ok(expr) + } + + fn equality(&mut self) -> ExprResult { + self.binary_operator( + &[TokenKind::BangEqual, TokenKind::EqualEqual], + Self::comparison, + ) + } + + fn comparison(&mut self) -> ExprResult { + self.binary_operator( + &[ + TokenKind::Greater, + TokenKind::GreaterEqual, + TokenKind::Less, + TokenKind::LessEqual, + ], + Self::term, + ) + } + + fn term(&mut self) -> ExprResult { + self.binary_operator(&[TokenKind::Minus, TokenKind::Plus], Self::factor) + } + + fn factor(&mut self) -> ExprResult { + self.binary_operator(&[TokenKind::Slash, TokenKind::Star], Self::unary) + } + + fn unary(&mut self) -> ExprResult { + if self.match_token(&TokenKind::Bang) || self.match_token(&TokenKind::Minus) { + return Ok(Expr::Unary(Unary { + operator: self.previous().clone(), + right: Box::new(self.unary()?), + })); + } + + return self.call(); + } + + fn call(&mut self) -> ExprResult { + let mut expr = self.primary()?; + + loop { + if self.match_token(&TokenKind::LeftParen) { + expr = self.finish_call(expr)?; + } else { + break; + } + } + + Ok(expr) + } + + fn finish_call(&mut self, callee: Expr) -> ExprResult { + let mut args = vec![]; + + if !self.check_token(&TokenKind::RightParen) { + loop { + // TODO(tazjin): Check for max args count + args.push(self.expression()?); + if !self.match_token(&TokenKind::Comma) { + break; + } + } + } + + let paren = self.consume( + &TokenKind::RightParen, + ErrorKind::ExpectedToken("Expect ')' after arguments."), + )?; + + Ok(Expr::Call(Call { + args, + callee: Box::new(callee), + paren, + })) + } + + fn primary(&mut self) -> ExprResult { + let next = self.advance(); + let literal = match next.kind { + TokenKind::True => Literal::Boolean(true), + TokenKind::False => Literal::Boolean(false), + TokenKind::Nil => Literal::Nil, + TokenKind::Number(num) => Literal::Number(num), + TokenKind::String(string) => Literal::String(string), + + TokenKind::LeftParen => { + let expr = self.expression()?; + self.consume(&TokenKind::RightParen, ErrorKind::UnmatchedParens)?; + return Ok(Expr::Grouping(Grouping(Box::new(expr)))); + } + + TokenKind::Identifier(_) => { + return Ok(Expr::Variable(Variable { + name: next, + depth: None, + })) + } + + unexpected => { + eprintln!("encountered {:?}", unexpected); + return Err(Error { + line: next.line, + kind: ErrorKind::ExpectedExpression(next.lexeme), + }); + } + }; + + Ok(Expr::Literal(literal)) + } + + // internal helpers + + fn identifier(&mut self, err: &'static str) -> Result<Token, Error> { + if let TokenKind::Identifier(_) = self.peek().kind { + Ok(self.advance()) + } else { + Err(Error { + line: self.peek().line, + kind: ErrorKind::ExpectedToken(err), + }) + } + } + + /// Check if the next token is in `oneof`, and advance if it is. + fn match_token(&mut self, token: &TokenKind) -> bool { + if self.check_token(token) { + self.advance(); + return true; + } + + false + } + + /// Return the next token and advance parser state. + fn advance(&mut self) -> Token { + if !self.is_at_end() { + self.current += 1; + } + + return self.previous().clone(); + } + + fn is_at_end(&self) -> bool { + self.check_token(&TokenKind::Eof) + } + + /// Is the next token `token`? + fn check_token(&self, token: &TokenKind) -> bool { + self.peek().kind == *token + } + + fn peek(&self) -> &Token { + &self.tokens[self.current] + } + + fn previous(&self) -> &Token { + &self.tokens[self.current - 1] + } + + fn consume(&mut self, kind: &TokenKind, err: ErrorKind) -> Result<Token, Error> { + if self.check_token(kind) { + return Ok(self.advance()); + } + + Err(Error { + line: self.peek().line, + kind: err, + }) + } + + fn synchronise(&mut self) { + self.advance(); + + while !self.is_at_end() { + if self.previous().kind == TokenKind::Semicolon { + return; + } + + match self.peek().kind { + TokenKind::Class + | TokenKind::Fun + | TokenKind::Var + | TokenKind::For + | TokenKind::If + | TokenKind::While + | TokenKind::Print + | TokenKind::Return => return, + + _ => { + self.advance(); + } + } + } + } + + fn binary_operator( + &mut self, + oneof: &[TokenKind], + each: fn(&mut Parser) -> ExprResult, + ) -> ExprResult { + let mut expr = each(self)?; + + while oneof.iter().any(|t| self.match_token(t)) { + expr = Expr::Binary(Binary { + left: Box::new(expr), + operator: self.previous().clone(), + right: Box::new(each(self)?), + }) + } + + return Ok(expr); + } +} + +pub fn parse(tokens: Vec<Token>) -> Result<Block, Vec<Error>> { + let mut parser = Parser { tokens, current: 0 }; + let mut program: Block = vec![]; + let mut errors: Vec<Error> = vec![]; + + while !parser.is_at_end() { + match parser.declaration() { + Err(err) => { + errors.push(err); + parser.synchronise(); + } + Ok(decl) => { + program.push(decl); + } + } + } + + if errors.is_empty() { + Ok(program) + } else { + Err(errors) + } +} diff --git a/users/tazjin/rlox/src/treewalk/resolver.rs b/users/tazjin/rlox/src/treewalk/resolver.rs index 5e15d386c73f..3d12973aa089 100644 --- a/users/tazjin/rlox/src/treewalk/resolver.rs +++ b/users/tazjin/rlox/src/treewalk/resolver.rs @@ -6,9 +6,9 @@ use std::collections::HashMap; use std::rc::Rc; -use crate::errors::{Error, ErrorKind}; -use crate::parser::{self, Expr, Statement}; -use crate::scanner::Token; +use crate::treewalk::errors::{Error, ErrorKind}; +use crate::treewalk::parser::{self, Expr, Statement}; +use crate::treewalk::scanner::Token; #[derive(Default)] struct Resolver<'a> { diff --git a/users/tazjin/rlox/src/treewalk/scanner.rs b/users/tazjin/rlox/src/treewalk/scanner.rs new file mode 100644 index 000000000000..af9075484145 --- /dev/null +++ b/users/tazjin/rlox/src/treewalk/scanner.rs @@ -0,0 +1,283 @@ +use crate::treewalk::errors::{Error, ErrorKind}; + +#[derive(Clone, Debug, PartialEq)] +pub enum TokenKind { + // Single-character tokens. + LeftParen, + RightParen, + LeftBrace, + RightBrace, + Comma, + Dot, + Minus, + Plus, + Semicolon, + Slash, + Star, + + // One or two character tokens. + Bang, + BangEqual, + Equal, + EqualEqual, + Greater, + GreaterEqual, + Less, + LessEqual, + + // Literals. + Identifier(String), + String(String), + Number(f64), + True, + False, + Nil, + + // Keywords. + And, + Class, + Else, + Fun, + For, + If, + Or, + Print, + Return, + Super, + This, + Var, + While, + + // Special things + Eof, +} + +#[derive(Clone, Debug)] +pub struct Token { + pub kind: TokenKind, + pub lexeme: String, + pub line: usize, +} + +struct Scanner<'a> { + source: &'a [char], + tokens: Vec<Token>, + errors: Vec<Error>, + start: usize, // offset of first character in current lexeme + current: usize, // current offset into source + line: usize, // current line in source +} + +impl<'a> Scanner<'a> { + fn is_at_end(&self) -> bool { + return self.current >= self.source.len(); + } + + fn advance(&mut self) -> char { + self.current += 1; + self.source[self.current - 1] + } + + fn add_token(&mut self, kind: TokenKind) { + let lexeme = &self.source[self.start..self.current]; + self.tokens.push(Token { + kind, + lexeme: lexeme.into_iter().collect(), + line: self.line, + }) + } + + fn scan_token(&mut self) { + match self.advance() { + // simple single-character tokens + '(' => self.add_token(TokenKind::LeftParen), + ')' => self.add_token(TokenKind::RightParen), + '{' => self.add_token(TokenKind::LeftBrace), + '}' => self.add_token(TokenKind::RightBrace), + ',' => self.add_token(TokenKind::Comma), + '.' => self.add_token(TokenKind::Dot), + '-' => self.add_token(TokenKind::Minus), + '+' => self.add_token(TokenKind::Plus), + ';' => self.add_token(TokenKind::Semicolon), + '*' => self.add_token(TokenKind::Star), + + // possible multi-character tokens + '!' => self.add_if_next('=', TokenKind::BangEqual, TokenKind::Bang), + '=' => self.add_if_next('=', TokenKind::EqualEqual, TokenKind::Equal), + '<' => self.add_if_next('=', TokenKind::LessEqual, TokenKind::Less), + '>' => self.add_if_next('=', TokenKind::GreaterEqual, TokenKind::Greater), + + '/' => { + // support comments until EOL by discarding characters + if self.match_next('/') { + while self.peek() != '\n' && !self.is_at_end() { + self.advance(); + } + } else { + self.add_token(TokenKind::Slash); + } + } + + // ignore whitespace + ws if ws.is_whitespace() => { + if ws == '\n' { + self.line += 1 + } + } + + '"' => self.scan_string(), + + digit if digit.is_digit(10) => self.scan_number(), + + chr if chr.is_alphabetic() || chr == '_' => self.scan_identifier(), + + unexpected => self.errors.push(Error { + line: self.line, + kind: ErrorKind::UnexpectedChar(unexpected), + }), + }; + } + + fn match_next(&mut self, expected: char) -> bool { + if self.is_at_end() || self.source[self.current] != expected { + false + } else { + self.current += 1; + true + } + } + + fn add_if_next(&mut self, expected: char, then: TokenKind, or: TokenKind) { + if self.match_next(expected) { + self.add_token(then); + } else { + self.add_token(or); + } + } + + fn peek(&self) -> char { + if self.is_at_end() { + return '\0'; + } else { + return self.source[self.current]; + } + } + + fn peek_next(&self) -> char { + if self.current + 1 >= self.source.len() { + return '\0'; + } else { + return self.source[self.current + 1]; + } + } + + fn scan_string(&mut self) { + while self.peek() != '"' && !self.is_at_end() { + if self.peek() == '\n' { + self.line += 1; + } + + self.advance(); + } + + if self.is_at_end() { + self.errors.push(Error { + line: self.line, + kind: ErrorKind::UnterminatedString, + }); + return; + } + + // closing '"' + self.advance(); + + // add token without surrounding quotes + let string: String = self.source[(self.start + 1)..(self.current - 1)] + .iter() + .collect(); + self.add_token(TokenKind::String(string)); + } + + fn scan_number(&mut self) { + while self.peek().is_digit(10) { + self.advance(); + } + + // Look for a fractional part + if self.peek() == '.' && self.peek_next().is_digit(10) { + // consume '.' + self.advance(); + + while self.peek().is_digit(10) { + self.advance(); + } + } + + let num: f64 = self.source[self.start..self.current] + .iter() + .collect::<String>() + .parse() + .expect("float parsing should always work"); + + self.add_token(TokenKind::Number(num)); + } + + fn scan_identifier(&mut self) { + while self.peek().is_alphanumeric() || self.peek() == '_' { + self.advance(); + } + + let ident: String = self.source[self.start..self.current].iter().collect(); + + // Determine whether this is an identifier, or a keyword: + let token_kind = match ident.as_str() { + "and" => TokenKind::And, + "class" => TokenKind::Class, + "else" => TokenKind::Else, + "false" => TokenKind::False, + "for" => TokenKind::For, + "fun" => TokenKind::Fun, + "if" => TokenKind::If, + "nil" => TokenKind::Nil, + "or" => TokenKind::Or, + "print" => TokenKind::Print, + "return" => TokenKind::Return, + "super" => TokenKind::Super, + "this" => TokenKind::This, + "true" => TokenKind::True, + "var" => TokenKind::Var, + "while" => TokenKind::While, + _ => TokenKind::Identifier(ident), + }; + + self.add_token(token_kind); + } + + fn scan_tokens(&mut self) { + while !self.is_at_end() { + self.start = self.current; + self.scan_token(); + } + + self.add_token(TokenKind::Eof); + } +} + +pub fn scan<'a>(input: &'a [char]) -> Result<Vec<Token>, Vec<Error>> { + let mut scanner = Scanner { + source: &input, + tokens: vec![], + errors: vec![], + start: 0, + current: 0, + line: 0, + }; + + scanner.scan_tokens(); + + if !scanner.errors.is_empty() { + return Err(scanner.errors); + } + + return Ok(scanner.tokens); +} |