wisp/src/parser.rs

use crate::{lexer::Token, list::List, value::Value};
use chumsky::{prelude::*, Stream};
use logos::{Lexer, Logos};

/// Parse source string into a value
pub fn read(src: &str) -> Result<Vec<Value>, Vec<Simple<Token<'_>>>> {
    parser().parse(stream_of_lexer(Token::lexer(src)))
}

fn parser<'a>() -> impl Parser<Token<'a>, Vec<Value<'a>>, Error = Simple<Token<'a>>> {
    recursive(|value| {
        let atom = select! {
            Token::Symbol("true") => Value::Bool(true),
            Token::Symbol("false") => Value::Bool(false),
            Token::Symbol("nil") => Value::Nil,
            Token::Symbol(s) => Value::Symbol(s.into()),
            Token::Keyword(k) => Value::Keyword(k.into()),
            Token::String(s) => Value::String(s.into()),
            Token::Number(n) => Value::Number(n),
        };

        let list = value
            .clone()
            .repeated()
            .map(List::from_vec)
            .map(Box::new)
            .map(Value::List)
            .delimited_by(just(Token::LeftParen), just(Token::RightParen));

        let vector = value
            .clone()
            .repeated()
            .map(Value::Vector)
            .delimited_by(just(Token::LeftBracket), just(Token::RightBracket));

        let map = value
            .clone()
            .then(value.clone())
            .repeated()
            .collect()
            .map(Value::Map)
            .delimited_by(just(Token::LeftCurly), just(Token::RightCurly));

        let quote = just(Token::Quote).ignore_then(value).map(|value| {
            Value::List(Box::new(List::Cons(
                Value::Symbol("quote".into()),
                Box::new(List::Cons(value, Box::new(List::Nil))),
            )))
        });

        atom.or(list).or(vector).or(map).or(quote)
    })
    .repeated()
    .then_ignore(end())
}

/// Convert Logos' Lexer into Chumsky'a Stream
fn stream_of_lexer<'a>(
    lexer: Lexer<'a, Token<'a>>,
) -> Stream<'_, Token<'_>, logos::Span, logos::SpannedIter<'_, Token<'_>>> {
    let len = lexer.source().len();
    Stream::from_iter(len..len + 1, lexer.spanned())
}