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|
use crate::{
lex::Token,
span::{Pos, Span, Spanned},
};
fn is_terminator(ch: char) -> bool {
ch.is_whitespace() || matches!(ch, '(' | ')' | '\'' | '"' | ';')
}
pub struct Lexer<'a> {
input: &'a str,
cursor: usize,
line: usize,
column: usize,
}
impl<'a> Lexer<'a> {
pub fn new(input: &'a str) -> Self {
Self {
input,
cursor: 0,
line: 1,
column: 0,
}
}
fn rest(&self) -> &str {
&self.input[self.cursor..]
}
fn peek(&self) -> Option<char> {
self.rest().chars().next()
}
fn peek_nth(&self, n: usize) -> Option<char> {
self.rest().chars().nth(n)
}
fn consume(&mut self) -> Option<char> {
let ch = self.peek()?;
self.cursor += ch.len_utf8();
if ch == '\n' {
self.line += 1;
self.column = 0;
} else {
self.column += 1;
}
Some(ch)
}
fn next_while(&mut self, mut predicate: impl FnMut(char) -> bool) -> &'a str {
let start = self.cursor;
while let Some(ch) = self.peek() {
if !predicate(ch) {
break;
}
self.consume();
}
&self.input[start..self.cursor]
}
fn next_atom(&mut self) -> &'a str {
self.next_while(|ch| !is_terminator(ch))
}
fn next_string(&mut self) -> Result<&'a str, &'a str> {
debug_assert_eq!(self.peek(), Some('"'));
self.consume();
let start = self.cursor;
while let Some(ch) = self.peek() {
match ch {
'"' => {
let string = &self.input[start..self.cursor];
self.consume();
return Ok(string);
}
'\n' => {
let string = &self.input[start..self.cursor];
self.consume();
return Err(string);
}
'\\' => {
self.consume();
self.consume();
}
_ => {
self.consume();
}
}
}
Err(&self.input[start..self.cursor])
}
}
impl<'a> Iterator for Lexer<'a> {
type Item = Spanned<Token<'a>>;
fn next(&mut self) -> Option<Self::Item> {
loop {
match self.peek()? {
ch if ch.is_whitespace() => {
self.next_while(char::is_whitespace);
}
';' => {
self.next_while(|ch| ch != '\n');
}
_ => break,
}
}
let start = Pos::new(self.line, self.column, self.cursor);
let token = match self.peek()? {
'(' => {
self.consume();
Token::LeftPar
}
')' => {
self.consume();
Token::RightPar
}
'\'' => {
self.consume();
Token::Quote
}
// Number
ch if ch.is_ascii_digit()
|| ch == '.' && self.peek_nth(1).is_some_and(|ch| ch.is_ascii_digit())
|| matches!(ch, '+' | '-')
&& self.peek_nth(1).is_some_and(|ch| ch.is_ascii_digit())
|| matches!(ch, '+' | '-')
&& self.peek_nth(1).is_some_and(|ch| ch == '.')
&& self.peek_nth(2).is_some_and(|ch| ch.is_ascii_digit()) =>
{
Token::Number(self.next_atom())
}
// String
'"' => match self.next_string() {
Ok(string) => Token::String(string),
Err(string) => Token::UnclosedString(string),
},
// Symbol
_ => Token::Symbol(self.next_atom()),
};
let end = Pos::new(self.line, self.column, self.cursor);
Some(Spanned::new(token, Span::new(start, end)))
}
}
|
