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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(String),
Number(f64),
// 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),
'/' => {
// 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
' ' => {}
'\r' => {}
'\t' => {}
'\n' => self.line += 1,
'"' => self.scan_string(),
digit if digit.is_digit(10) => self.scan_number(),
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_tokens(mut self) -> Vec<Token<'a>> {
while !self.is_at_end() {
self.start = self.current;
self.scan_token();
}
return self.tokens;
}
}
pub fn scan<'a>(input: &'a [char]) -> Vec<Token<'a>> {
let scanner = Scanner {
source: &input,
tokens: vec![],
errors: vec![],
start: 0,
current: 0,
line: 0,
};
return scanner.scan_tokens();
}
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