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|
use std::{iter::Peekable, result};
use crate::{
ast::{Atom, Error, Expr, Program},
lexer::Token,
span::{Pos, Span, Spanned},
};
type Result<T> = result::Result<T, Spanned<Error>>;
fn parse_number(number: &str) -> Atom {
let is_float = number.bytes().any(|b| matches!(b, b'.' | b'e' | b'E'));
if is_float {
match number.parse() {
Ok(ok) => Atom::Float(ok),
Err(err) => todo!("invalid float literal {number}: {err}"),
}
} else {
match number.parse() {
Ok(ok) => Atom::Integer(ok),
Err(err) => todo!("invalid integer literal {number}: {err}"),
}
}
}
fn parse_string(string: &str) -> Atom {
let mut result = String::new();
let mut is_escape = false;
for ch in string.chars() {
if !is_escape {
match ch {
'\\' => is_escape = true,
_ => result.push(ch),
}
} else {
match ch {
'"' => result.push('"'),
'n' => result.push('\n'),
'\\' => result.push('\\'),
'\n' => {}
_ => todo!("unexpected escape char {ch:?}"),
}
is_escape = false;
}
}
if is_escape {
todo!("unclosed string");
}
Atom::String(result.into())
}
fn parse_symbol(symbol: &str) -> Atom {
match symbol {
"true" => Atom::Bool(true),
"false" => Atom::Bool(false),
"nil" => Atom::Nil,
_ => Atom::Symbol(symbol.into()),
}
}
pub struct Parser<'a, I>
where
I: Iterator<Item = Spanned<Token<'a>>>,
{
tokens: Peekable<I>,
last_token_end: Pos,
}
impl<'a, I> Parser<'a, I>
where
I: Iterator<Item = Spanned<Token<'a>>>,
{
pub fn new(tokens: I) -> Self {
Self {
tokens: tokens.peekable(),
last_token_end: Pos::new(1, 0, 0),
}
}
fn peek(&mut self) -> Option<Spanned<Token<'a>>> {
self.tokens.peek().copied()
}
fn consume(&mut self) -> Option<Spanned<Token<'a>>> {
self.tokens
.next()
.inspect(|s| self.last_token_end = s.span.end)
}
fn parse_expr(&mut self) -> Result<Spanned<Expr>> {
let Spanned { inner: token, span } = match self.peek() {
Some(spanned) => spanned,
None => todo!("unexpected eof"),
};
let expr = match token {
Token::LeftPar => {
self.consume();
let list = self.parse_list()?;
let expr = if !list.is_empty() {
Expr::List(list)
} else {
Expr::Atom(Atom::Nil)
};
Spanned::new(expr, Span::new(span.start, self.last_token_end))
}
Token::RightPar => todo!("unexpected par"),
Token::Quote => {
self.consume();
let quote = Spanned::new(
Expr::Atom(Atom::Symbol("quote".into())),
Span::new(span.start, self.last_token_end),
);
let expr = self.parse_expr()?;
Spanned::new(
Expr::List(vec![quote, expr]),
Span::new(span.start, self.last_token_end),
)
}
Token::Number(number) => {
self.consume();
Spanned::new(
Expr::Atom(parse_number(number)),
Span::new(span.start, self.last_token_end),
)
}
Token::String(string) => {
self.consume();
Spanned::new(
Expr::Atom(parse_string(string)),
Span::new(span.start, self.last_token_end),
)
}
Token::UnclosedString(string) => {
self.consume();
todo!("unclosed string {string:?}")
}
Token::Symbol(symbol) => {
self.consume();
Spanned::new(
Expr::Atom(parse_symbol(symbol)),
Span::new(span.start, self.last_token_end),
)
}
};
Ok(expr)
}
fn parse_list(&mut self) -> Result<Vec<Spanned<Expr>>> {
let mut list = Vec::new();
while let Some(Spanned { inner: token, .. }) = self.peek() {
match token {
Token::RightPar => {
self.consume();
return Ok(list);
}
_ => list.push(self.parse_expr()?),
}
}
todo!("unclosed par")
}
pub fn parse(mut self) -> Result<Program> {
let mut program = Vec::new();
while self.peek().is_some() {
program.push(self.parse_expr()?)
}
Ok(Program(program))
}
}
|
