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263 lines
7.5 KiB
Rust
263 lines
7.5 KiB
Rust
use std::fmt;
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use std::str::Chars;
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mod cursor;
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use cursor::Cursor;
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pub(crate) mod token;
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use token::Token;
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pub struct Lexer<'a> {
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cursor: Cursor<'a>,
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history: Vec<Token>,
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offset: usize,
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token_line: usize,
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token_col: usize,
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}
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static NUMERALS: [char; 16] = [
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'0', '1', '2', '3', '4', '5', '6', '7', '8', '9', 'a', 'b', 'c', 'd', 'e', 'f',
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];
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struct KeywordMap {
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raw: &'static str,
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kind: token::Kind,
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}
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const fn kw(raw: &'static str, kind: token::Kind) -> KeywordMap {
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KeywordMap { raw, kind }
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}
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static KEYWORDS: [KeywordMap; 6] = [
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kw("depend", token::Kind::DependKeyword),
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kw("include", token::Kind::IncludeKeyword),
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kw("module", token::Kind::ModuleKeyword),
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kw("set", token::Kind::SetKeyword),
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kw("source", token::Kind::SourceKeyword),
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kw("type", token::Kind::TypeKeyword),
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];
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impl Iterator for Lexer<'_> {
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type Item = Result<Token, SyntaxError>;
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fn next(&mut self) -> Option<Result<Token, SyntaxError>> {
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if self.offset > 0 {
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let tmp = self.history[self.history.len() - self.offset];
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self.offset -= 1;
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return Some(Ok(tmp));
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}
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let result = match self.cursor.next()? {
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c if c.is_ascii_whitespace() => {
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self.cursor.skip_whitespace();
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self.cursor.chop();
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self.next()?
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}
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',' => self.token_ok(token::Kind::Comma),
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';' => self.token_ok(token::Kind::Semi),
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'{' => self.token_ok(token::Kind::OBrace),
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'}' => self.token_ok(token::Kind::CBrace),
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'[' => self.token_ok(token::Kind::OBracket),
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']' => self.token_ok(token::Kind::CBracket),
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'=' => self.token_ok(token::Kind::Eq),
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'+' => self.token_ok(token::Kind::Plus),
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'-' => self.token_ok(token::Kind::Minus),
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'*' => self.token_ok(token::Kind::Asterisk),
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'/' => self.token_ok(token::Kind::Slash),
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'%' => self.token_ok(token::Kind::Percent),
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'#' => {
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self.read_comment();
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// we don't need comments for now and they would
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// only confuse the parser so let's just Not
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self.next()?
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}
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'"' => self.read_string_literal(),
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'0' => self.read_prefix_int_literal(),
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_c @ '1'..='9' => self.read_int_literal(10),
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_c @ 'A'..='Z' => self.read_ident(),
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_c @ 'a'..='z' => self.read_keyword_or_ident(), // keywords are always lowercase
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c => self.syntax_error(format!("Unexpected character '{}'", c)),
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};
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if let Ok(token) = result {
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self.history.push(token);
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}
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Some(result)
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}
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}
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impl<'a> Lexer<'a> {
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pub fn new(stream: Chars<'a>) -> Lexer<'a> {
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Lexer {
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cursor: Cursor::new(stream),
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history: Vec::new(),
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offset: 0,
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token_line: 1,
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token_col: 1,
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}
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}
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pub fn peek(&mut self) -> Option<Result<Token, SyntaxError>> {
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let t = self.next()?;
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self.prev();
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Some(t)
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}
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pub fn prev(&mut self) -> Option<&Token> {
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let prev = self.history.last()?;
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self.offset += 1;
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Some(prev)
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}
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pub fn expect_kind(&mut self, kind: token::Kind) -> Result<Token, SyntaxError> {
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match self.next() {
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Some(t) => if t?.kind == kind {
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Ok(t?)
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} else {
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self.syntax_error(format!("Expected {}, got {}", kind, t?.kind))
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}
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None => self.syntax_error("Unexpected EOF"),
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}
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}
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pub fn require_next(&mut self) -> Result<Token, SyntaxError> {
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match self.next() {
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Some(t) => t,
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None => self.syntax_error("Unexpected EOF"),
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}
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}
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fn read_keyword_or_ident(&mut self) -> Result<Token, SyntaxError> {
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let current = self.cursor.current().unwrap();
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for kw in &KEYWORDS {
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// keywords are always at least 2 characters long as per the language spec
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let first_char = kw.raw.chars().next().unwrap();
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if current == first_char && self.skip_if_match(&kw.raw[1..]) {
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return self.token_ok(kw.kind);
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}
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}
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self.read_ident()
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}
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fn read_ident(&mut self) -> Result<Token, SyntaxError> {
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for c in &mut self.cursor {
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if !c.is_ascii_alphanumeric() && c != '_' {
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self.cursor.prev();
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break;
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}
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}
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self.token_ok(token::Kind::Ident)
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}
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fn read_comment(&mut self) -> Result<Token, SyntaxError> {
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self.cursor.seek_while(|c| c != '\n');
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self.token_ok(token::Kind::Comment)
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}
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fn read_string_literal(&mut self) -> Result<Token, SyntaxError> {
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assert!(self.cursor.current() == Some('"'));
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self.cursor.chop();
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let mut raw = String::new();
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for c in &mut self.cursor {
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// TODO: string escape sequences are a thing
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if c == '"' {
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self.cursor.chop();
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return self.token_raw_ok(token::Kind::StringLiteral, raw);
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} else {
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raw.push(c);
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}
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}
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self.token_ok(token::Kind::StringLiteral)
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}
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fn read_prefix_int_literal(&mut self) -> Result<Token, SyntaxError> {
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assert!(self.cursor.next() == Some('0'));
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match self.cursor.next() {
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Some('x') => self.read_int_literal(16),
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Some('o') => self.read_int_literal(8),
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Some('b') => self.read_int_literal(2),
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Some(c) => self.syntax_error(format!("Unexpected character '{}'", c)),
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None => self.syntax_error("Unexpected end-of-file"),
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}
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}
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fn read_int_literal(&mut self, base: usize) -> Result<Token, SyntaxError> {
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assert!(base >= 2 && base <= 16);
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for c in &mut self.cursor {
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if !NUMERALS[0..base].contains(&c.to_ascii_lowercase()) {
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self.cursor.prev();
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break;
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}
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}
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self.token_ok(token::Kind::IntLiteral)
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}
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fn token(&mut self, kind: token::Kind, raw: String) -> Token {
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let t = Token {
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kind,
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line: self.token_line,
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col: self.token_col,
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raw: raw,
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};
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self.token_line = self.cursor.line();
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self.token_col = self.cursor.col();
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t
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}
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fn token_ok<T>(&mut self, kind: token::Kind) -> Result<Token, T> {
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let raw = self.cursor.chop();
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Ok(self.token(kind, raw))
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}
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fn token_raw_ok<T>(&mut self, kind: token::Kind, raw: String) -> Result<Token, T> {
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Ok(self.token(kind, raw))
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}
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fn skip_if_match(&mut self, s: &str) -> bool {
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let mut n: usize = 0;
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for c in s.chars() {
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if self.cursor.next() == Some(c) {
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n += 1;
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} else {
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self.cursor.seek_back(n);
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return false;
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}
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}
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true
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}
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fn syntax_error<T>(&mut self, msg: &str) -> Result<T, SyntaxError> {
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Err(SyntaxError {
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line: self.cursor.line(),
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col: self.cursor.col(),
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msg: String::from(msg),
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})
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}
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}
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#[derive(Debug)]
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pub struct SyntaxError {
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pub line: usize,
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pub col: usize,
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pub msg: String,
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}
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impl fmt::Display for SyntaxError {
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fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
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write!(
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f,
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"SyntaxError in {}:{}: {}",
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self.line,
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self.col,
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self.msg.as_str()
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)
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}
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}
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