300 lines
9.3 KiB
Rust
300 lines
9.3 KiB
Rust
use std::collections::HashMap;
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use lazy_static::lazy_static;
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use crate::{
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tokens::{Token, TokenType},
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ErrorHandler,
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};
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lazy_static! {
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/// A map of keywords to token types.
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static ref KEYWORDS: HashMap<&'static str, TokenType> = {
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let mut keywords = HashMap::new();
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keywords.insert("and", TokenType::And);
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keywords.insert("class", TokenType::Class);
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keywords.insert("else", TokenType::Else);
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keywords.insert("false", TokenType::False);
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keywords.insert("for", TokenType::For);
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keywords.insert("fun", TokenType::Fun);
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keywords.insert("if", TokenType::If);
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keywords.insert("nil", TokenType::Nil);
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keywords.insert("or", TokenType::Or);
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keywords.insert("print", TokenType::Print);
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keywords.insert("return", TokenType::Return);
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keywords.insert("super", TokenType::Super);
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keywords.insert("this", TokenType::This);
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keywords.insert("true", TokenType::True);
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keywords.insert("var", TokenType::Var);
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keywords.insert("while", TokenType::While);
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keywords
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};
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}
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/// The scanner's state, including the source it is scanning.
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pub struct Scanner {
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source: String,
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tokens: Vec<Token>,
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start: usize,
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current: usize,
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len: usize,
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line: usize,
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}
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impl Scanner {
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/// Initialize a scanner by specifying the source code to scan.
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pub fn new(source: String) -> Scanner {
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let len = source.chars().count();
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Scanner {
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source,
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tokens: Vec::new(),
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start: 0,
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current: 0,
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len,
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line: 1,
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}
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}
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/// Scan the source code, generating the list of tokens and returning it.
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/// The scanner itself is destroyed once the process is complete.
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pub fn scan_tokens(mut self, err_hdl: &mut ErrorHandler) -> Vec<Token> {
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while !self.is_at_end() {
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self.start = self.current;
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self.scan_token(err_hdl);
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}
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self.tokens
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}
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/// Read the next token from the input
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fn scan_token(&mut self, err_hdl: &mut ErrorHandler) {
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match self.advance() {
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// Single-character tokens
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'(' => self.add_token(TokenType::LeftParen),
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')' => self.add_token(TokenType::RightParen),
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'{' => self.add_token(TokenType::LeftBrace),
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'}' => self.add_token(TokenType::RightBrace),
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',' => self.add_token(TokenType::Comma),
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'.' => self.add_token(TokenType::Dot),
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'-' => self.add_token(TokenType::Minus),
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'+' => self.add_token(TokenType::Plus),
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';' => self.add_token(TokenType::Semicolon),
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'*' => self.add_token(TokenType::Star),
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// Slash is a special case as it may be a line comment
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'/' => {
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if self.is_match('/') {
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while self.peek() != '\n' && !self.is_at_end() {
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self.current += 1;
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}
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} else if self.is_match('*') {
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self.block_comment(err_hdl);
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} else {
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self.add_token(TokenType::Slash)
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}
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}
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// Things that may be either alone or followed by '='
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'!' => {
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if self.is_match('=') {
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self.add_token(TokenType::BangEqual)
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} else {
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self.add_token(TokenType::Bang)
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}
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}
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'=' => {
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if self.is_match('=') {
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self.add_token(TokenType::EqualEqual)
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} else {
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self.add_token(TokenType::Equal)
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}
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}
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'<' => {
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if self.is_match('=') {
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self.add_token(TokenType::LessEqual)
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} else {
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self.add_token(TokenType::Less)
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}
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}
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'>' => {
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if self.is_match('=') {
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self.add_token(TokenType::GreaterEqual)
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} else {
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self.add_token(TokenType::Greater)
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}
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}
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// String litterals
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'"' => self.string_litteral(err_hdl),
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// Handle whitespace
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' ' | '\r' | '\t' => (),
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'\n' => self.line += 1,
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// Numbers
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ch if ch.is_digit(10) => self.number(err_hdl),
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// Identifiers
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ch if ch.is_ascii_alphabetic() => self.identifier(),
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// Anything else is an error
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ch => err_hdl.error(self.line, &format!("unexpected character {:#?}", ch)),
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}
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}
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/// Read the rest of a string litteral
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fn string_litteral(&mut self, err_hdl: &mut ErrorHandler) {
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loop {
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let p = self.peek();
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if p == '"' || self.is_at_end() {
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break;
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}
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if p == '\n' {
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self.line += 1;
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}
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self.current += 1;
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}
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if self.is_at_end() {
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err_hdl.error(self.line, "unterminated string");
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} else {
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self.current += 1; // Last '"'
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let value = self.get_substring(self.start + 1, self.current - 1);
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self.add_token(TokenType::String(value));
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}
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}
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/// Read the rest of a number.
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fn number(&mut self, err_hdl: &mut ErrorHandler) {
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while self.peek().is_digit(10) {
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self.current += 1;
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}
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if self.peek() == '.' && self.peek_next().is_digit(10) {
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self.current += 1;
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while self.peek().is_digit(10) {
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self.current += 1;
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}
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}
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let tok_string = self.get_substring(self.start, self.current);
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match tok_string.parse::<f64>() {
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Err(e) => {
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err_hdl.error(
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self.line,
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&format!(
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"Could not parse {} as a floating point number: {:?}",
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tok_string, e
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),
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);
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}
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Ok(value) => {
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self.add_token(TokenType::Number(value));
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}
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};
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}
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/// Read the rest of an identifier or keyword.
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fn identifier(&mut self) {
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while is_word_char(self.peek()) {
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self.current += 1;
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}
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let word = self.get_substring(self.start, self.current);
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match KEYWORDS.get(&word as &str) {
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Some(tt) => self.add_token(tt.clone()),
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None => self.add_token(TokenType::Identifier(word)),
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}
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}
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/// Read (and ignore) a block comment. Block comments may be nested.
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fn block_comment(&mut self, err_hdl: &mut ErrorHandler) {
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let mut depth = 1;
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loop {
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if self.is_at_end() {
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err_hdl.error(self.line, "unterminated block comment");
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return
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}
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let cur = self.advance();
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let next = self.peek();
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if cur == '*' && next == '/' {
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depth -= 1;
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self.current += 1;
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if depth == 0 {
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return;
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}
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} else if cur == '/' && next == '*' {
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depth += 1;
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self.current += 1;
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} else if cur == '\n' {
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self.line += 1;
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}
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}
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}
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/// Check whether the end of the input has been reached.
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fn is_at_end(&self) -> bool {
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self.current >= self.len
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}
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/// Advance to the next character and return it.
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fn advance(&mut self) -> char {
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let ch = self.cur_char();
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self.current += 1;
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ch
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}
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/// Consume the current character if it matches the argument.
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fn is_match(&mut self, expected: char) -> bool {
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if self.is_at_end() {
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false
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} else if self.cur_char() == expected {
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self.current += 1;
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true
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} else {
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false
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}
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}
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/// Returns the current character, or a NULL character if the end has been
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/// reached.
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fn peek(&self) -> char {
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if self.is_at_end() {
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'\0'
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} else {
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self.cur_char()
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}
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}
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/// Returns the next character, or a NULL character if the end has been
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/// reached.
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fn peek_next(&self) -> char {
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if self.current + 1 >= self.source.chars().count() {
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'\0'
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} else {
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self.source.chars().nth(self.current + 1).unwrap()
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}
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}
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/// Read the current character.
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fn cur_char(&self) -> char {
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self.source.chars().nth(self.current).unwrap()
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}
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/// Add a token to the output.
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fn add_token(&mut self, token_type: TokenType) {
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let lexeme = self.get_substring(self.start, self.current);
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let token = Token {
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token_type,
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lexeme,
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line: self.line,
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};
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self.tokens.push(token)
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}
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/// Get a substring from the source.
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fn get_substring(&self, start: usize, end: usize) -> String {
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assert!(start <= end);
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self.source
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.chars()
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.skip(start)
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.take(end - start)
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.collect::<String>()
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}
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}
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/// Check whether a character is either alphanumeric or an underscore.
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fn is_word_char(c: char) -> bool {
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c.is_ascii_alphanumeric() || c == '_'
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}
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