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//! The lexer: source text in, a flat list of tokens out.
//!
//! It scans byte by byte. Whitespace and `//` comments are skipped. Numbers,
//! strings, identifiers/keywords, and operators each get their own little
//! routine. Every token remembers the byte range it came from.
use crate::diagnostic::{LuxError, Span};
#[derive(Debug, Clone, PartialEq)]
pub enum Tok {
// literals
Int(i64),
Float(f64),
Str(String),
True,
False,
Ident(String),
// keywords
Let,
Var,
If,
Else,
While,
For,
In,
Func,
Return,
Struct,
Enum,
Match,
// punctuation
LParen,
RParen,
LBrace,
RBrace,
LBracket,
RBracket,
Colon,
Comma,
Dot,
DotDot,
Arrow,
FatArrow,
// operators
Plus,
Minus,
Star,
Slash,
Percent,
Eq,
PlusEq,
MinusEq,
EqEq,
NotEq,
Lt,
Gt,
Le,
Ge,
AndAnd,
OrOr,
Bang,
// end of input
Eof,
}
#[derive(Debug, Clone)]
pub struct Token {
pub tok: Tok,
pub span: Span,
}
pub fn lex(source: &str) -> Result<Vec<Token>, LuxError> {
let bytes = source.as_bytes();
let n = bytes.len();
let mut tokens = Vec::new();
let mut i = 0;
while i < n {
let c = bytes[i];
// whitespace
if c == b' ' || c == b'\t' || c == b'\r' || c == b'\n' {
i += 1;
continue;
}
// line comment
if c == b'/' && i + 1 < n && bytes[i + 1] == b'/' {
while i < n && bytes[i] != b'\n' {
i += 1;
}
continue;
}
let start = i;
// number: int or float
if c.is_ascii_digit() {
while i < n && bytes[i].is_ascii_digit() {
i += 1;
}
// A `.` here means a decimal point — unless it's `..`, the start of
// a range like `0..5`, in which case this number is a plain int.
if i < n && bytes[i] == b'.' && !(i + 1 < n && bytes[i + 1] == b'.') {
if i + 1 < n && bytes[i + 1].is_ascii_digit() {
i += 1; // consume the dot
while i < n && bytes[i].is_ascii_digit() {
i += 1;
}
let text = &source[start..i];
let val: f64 = text
.parse()
.map_err(|_| LuxError::new("invalid float literal", Span::new(start, i)))?;
tokens.push(Token {
tok: Tok::Float(val),
span: Span::new(start, i),
});
continue;
} else {
return Err(LuxError::new(
"a float needs at least one digit after the decimal point",
Span::new(start, i + 1),
)
.with_note("write 3.0, not 3."));
}
}
let text = &source[start..i];
let val: i64 = text
.parse()
.map_err(|_| LuxError::new("integer literal is too large", Span::new(start, i)))?;
tokens.push(Token {
tok: Tok::Int(val),
span: Span::new(start, i),
});
continue;
}
// identifier or keyword
if c.is_ascii_alphabetic() || c == b'_' {
while i < n && (bytes[i].is_ascii_alphanumeric() || bytes[i] == b'_') {
i += 1;
}
let text = &source[start..i];
let tok = match text {
"let" => Tok::Let,
"var" => Tok::Var,
"if" => Tok::If,
"else" => Tok::Else,
"while" => Tok::While,
"for" => Tok::For,
"in" => Tok::In,
"func" => Tok::Func,
"return" => Tok::Return,
"struct" => Tok::Struct,
"enum" => Tok::Enum,
"match" => Tok::Match,
"true" => Tok::True,
"false" => Tok::False,
_ => Tok::Ident(text.to_string()),
};
tokens.push(Token {
tok,
span: Span::new(start, i),
});
continue;
}
// string literal
if c == b'"' {
i += 1; // opening quote
let mut s = String::new();
loop {
if i >= n {
return Err(LuxError::new("unterminated string", Span::new(start, i))
.with_note("add a closing \" to the end of the string"));
}
let ch = bytes[i];
if ch == b'"' {
i += 1; // closing quote
break;
}
if ch == b'\\' {
if i + 1 >= n {
return Err(LuxError::new("unterminated string", Span::new(start, i)));
}
let mapped = match bytes[i + 1] {
b'n' => '\n',
b't' => '\t',
b'"' => '"',
b'\\' => '\\',
other => {
return Err(LuxError::new(
format!("unknown escape sequence \\{}", other as char),
Span::new(i, i + 2),
)
.with_note("lux understands \\n, \\t, \\\" and \\\\"));
}
};
s.push(mapped);
i += 2;
continue;
}
// ordinary character (handle multi-byte UTF-8 safely)
let rest = &source[i..];
let ch_char = rest.chars().next().unwrap();
s.push(ch_char);
i += ch_char.len_utf8();
}
tokens.push(Token {
tok: Tok::Str(s),
span: Span::new(start, i),
});
continue;
}
// two-character operators (compared as bytes to avoid splitting UTF-8)
let c1 = if i + 1 < n { bytes[i + 1] } else { 0 };
let two = match (c, c1) {
(b'=', b'=') => Some(Tok::EqEq),
(b'!', b'=') => Some(Tok::NotEq),
(b'<', b'=') => Some(Tok::Le),
(b'>', b'=') => Some(Tok::Ge),
(b'&', b'&') => Some(Tok::AndAnd),
(b'|', b'|') => Some(Tok::OrOr),
(b'+', b'=') => Some(Tok::PlusEq),
(b'-', b'=') => Some(Tok::MinusEq),
(b'-', b'>') => Some(Tok::Arrow),
(b'=', b'>') => Some(Tok::FatArrow),
(b'.', b'.') => Some(Tok::DotDot),
_ => None,
};
if let Some(t) = two {
tokens.push(Token {
tok: t,
span: Span::new(start, i + 2),
});
i += 2;
continue;
}
// single-character tokens
let single = match c {
b'(' => Tok::LParen,
b')' => Tok::RParen,
b'{' => Tok::LBrace,
b'}' => Tok::RBrace,
b'[' => Tok::LBracket,
b']' => Tok::RBracket,
b':' => Tok::Colon,
b',' => Tok::Comma,
b'.' => Tok::Dot,
b'+' => Tok::Plus,
b'-' => Tok::Minus,
b'*' => Tok::Star,
b'/' => Tok::Slash,
b'%' => Tok::Percent,
b'=' => Tok::Eq,
b'<' => Tok::Lt,
b'>' => Tok::Gt,
b'!' => Tok::Bang,
other => {
return Err(LuxError::new(
format!("unexpected character '{}'", other as char),
Span::new(start, start + 1),
));
}
};
tokens.push(Token {
tok: single,
span: Span::new(start, start + 1),
});
i += 1;
}
tokens.push(Token {
tok: Tok::Eof,
span: Span::new(n, n),
});
Ok(tokens)
}