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pub struct Lexer<'a> {
pub buf: &'a str,
}
impl<'a> Lexer<'a> {
fn skip_whitespace(&mut self) {
while let Some(b' ') = self.buf.as_bytes().first() {
self.buf = &self.buf[1..];
}
}
fn parse_num(&mut self) -> &'a str {
let mut i = 0;
while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
i += 1;
}
if let Some(b'.') = self.buf.as_bytes().get(i) {
i += 1;
}
while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
i += 1;
}
let (Some(b'e') | Some(b'E')) = self.buf.as_bytes().get(i) else {
let t = &self.buf[..i];
self.buf = &self.buf[i..];
return t;
};
i += 1;
if let Some(b'-') = self.buf.as_bytes().get(i) {
i += 1;
}
while matches!(self.buf.as_bytes().get(i), Some(&b) if b.is_ascii_digit()) {
i += 1;
}
let t = &self.buf[..i];
self.buf = &self.buf[i..];
t
}
}
impl<'a> Iterator for Lexer<'a> {
type Item = &'a str;
fn next(&mut self) -> Option<&'a str> {
self.skip_whitespace();
if self.buf.starts_with("//") {
self.buf = &self.buf[2..];
return Some("//");
}
Some(match self.buf.as_bytes().first()? {
b'0'..=b'9' | b'.' => self.parse_num(),
b'a'..=b'z' | b'A'..=b'Z' => {
let mut i = 1;
while let Some(b'a'..=b'z' | b'A'..=b'Z' | b'0'..=b'9') = self.buf.as_bytes().get(i)
{
i += 1;
}
let t = &self.buf[..i];
self.buf = &self.buf[i..];
t
}
_ => {
let mut i = 1;
while !self.buf.is_char_boundary(i) {
i += 1;
}
let t = &self.buf[..i];
self.buf = &self.buf[i..];
t
}
})
}
}
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