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use crate::errors::{Error, ErrorKind};
#[derive(Debug)]
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,
Number,
// Keywords.
And,
Class,
Else,
False,
Fun,
For,
If,
Nil,
Or,
Print,
Return,
Super,
This,
True,
Var,
While,
// Special things
Eof,
}
#[derive(Debug)]
pub struct Token<'a> {
kind: TokenKind,
lexeme: &'a [char],
// literal: Object, // TODO(tazjin): Uhh?
line: usize,
}
struct Scanner<'a> {
source: &'a [char],
tokens: Vec<Token<'a>>,
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,
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),
unexpected => self.errors.push(Error {
line: self.line,
kind: ErrorKind::UnexpectedChar(unexpected),
}),
};
}
fn add_if_next(&mut self, expected:char, then: TokenKind, or: TokenKind) {
if self.is_at_end() || self.source[self.current] != expected {
self.add_token(or);
} else {
self.current += 1;
self.add_token(then);
}
}
fn scan_tokens(mut self) -> Vec<Token<'a>> {
while !self.is_at_end() {
self.start = self.current;
self.scan_token();
}
return self.tokens;
}
}
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