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use std::io::{self, BufRead, ErrorKind, Read};
use std::str::FromStr;
use super::parser;
#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum CharKind {
Number,
Alpha,
Punct,
String,
Comment,
}
pub struct Lexer<R> {
rdr: R,
current: Option<(CharKind, Vec<u8>)>,
}
impl CharKind {
fn of(b: u8) -> Option<CharKind> {
match b {
b'a'..=b'z' | b'A'..=b'Z' | b'_' => Some(CharKind::Alpha),
b'0'..=b'9' => Some(CharKind::Number),
b' ' | b'\r' | b'\n' | b'\t' => None,
//any other ASCII character is a punct
x if x < 0x80 => Some(CharKind::Punct),
//non ASCII characters are considered letters for tokenization purposes
_ => Some(CharKind::Alpha),
}
}
}
impl<R: BufRead> Lexer<R> {
pub fn new(rdr: R) -> Self {
Lexer { rdr, current: None }
}
fn next_priv(&mut self) -> io::Result<Option<(CharKind, Vec<u8>)>> {
let mut reply = None;
while reply.is_none() {
let b = match self.rdr.by_ref().bytes().next() {
Some(b) => b?,
None => {
//EOF: if there is a current token, return it now
let res = self.current.take();
return Ok(res);
}
};
let k2 = CharKind::of(b);
self.current = match (self.current.take(), k2) {
(None, None) => None,
(None, Some(k2)) => Some((k2, vec![b])),
(Some((k1, mut bs)), t2) => {
//extend a Number or Alpha, but not a Punct
if Some(k1) == t2 && k1 != CharKind::Punct {
bs.push(b);
Some((k1, bs))
} else {
//check special Puncts
if k1 == CharKind::Punct && bs[0] == b'"' {
//string
let text = if b != b'"' {
let mut text = vec![b];
self.rdr.by_ref().read_until(b'"', &mut text)?;
if text.pop().unwrap() != b'"' {
return Err(ErrorKind::InvalidInput.into());
}
text
} else {
vec![]
};
reply = Some((CharKind::String, text));
None
} else if k1 == CharKind::Punct && bs[0] == b'/' && b == b'/' {
//comment
let mut text = vec![];
self.rdr.by_ref().read_until(b'\n', &mut text)?;
reply = Some((CharKind::Comment, text));
None
} else {
//The current token is returned and the new lookahead is stored
reply = Some((k1, bs));
t2.map(|k2| (k2, vec![b]))
}
}
}
}
}
Ok(reply)
}
fn next_token(&mut self) -> io::Result<Option<parser::Token>> {
loop {
let token = self.next_priv()?;
let token = match token {
None => None,
Some((kind, s)) => {
let reply = match kind {
CharKind::Comment => continue,
CharKind::Number => {
let s = String::from_utf8(s).map_err(|_| ErrorKind::InvalidInput)?;
parser::Token::Number(
i64::from_str(&s).map_err(|_| ErrorKind::InvalidInput)?,
)
}
CharKind::Alpha => match &s[..] {
b"fn" => parser::Token::Fn,
b"var" => parser::Token::Var,
b"if" => parser::Token::If,
b"else" => parser::Token::Else,
b"while" => parser::Token::While,
b"return" => parser::Token::Return,
b"continue" => parser::Token::Continue,
b"break" => parser::Token::Break,
b"and" => parser::Token::And,
b"or" => parser::Token::Or,
b"not" => parser::Token::Not,
_ => {
let s =
String::from_utf8(s).map_err(|_| ErrorKind::InvalidInput)?;
parser::Token::Ident(s)
}
},
CharKind::String => {
let s = String::from_utf8(s).map_err(|_| ErrorKind::InvalidInput)?;
parser::Token::String(s)
}
CharKind::Punct => {
let s = s[0];
//First check for two-char Puncts
let tt = if let Some((CharKind::Punct, n)) = &self.current {
let n = n[0];
match (s, n) {
(b'=', b'=') => Some(parser::Token::Equal),
(b'!', b'=') => Some(parser::Token::NotEqual),
(b'<', b'=') => Some(parser::Token::LessEq),
(b'>', b'=') => Some(parser::Token::GreaterEq),
_ => None,
}
} else {
None
};
if tt.is_some() {
self.current = None;
return Ok(tt);
}
match s {
b'(' => parser::Token::LParen,
b')' => parser::Token::RParen,
b'{' => parser::Token::LBrace,
b'}' => parser::Token::RBrace,
b',' => parser::Token::Comma,
b';' => parser::Token::Semicolon,
b'=' => parser::Token::Assign,
b'+' => parser::Token::Plus,
b'-' => parser::Token::Minus,
b'*' => parser::Token::Mult,
b'/' => parser::Token::Div,
b'<' => parser::Token::Less,
b'>' => parser::Token::Greater,
_ => return Err(ErrorKind::InvalidInput.into()),
}
}
};
Some(reply)
}
};
break Ok(token);
}
}
}
impl<R: BufRead> Iterator for Lexer<R> {
type Item = io::Result<parser::Token>;
fn next(&mut self) -> Option<Self::Item> {
self.next_token().transpose()
}
}