sybil/src/syn/parser.rs

use crate::syn::{ast::*, error::*, lexer::*, token::*};

// /////////////////////////////////////////////////////////////////////////////
// Parser
// /////////////////////////////////////////////////////////////////////////////

#[derive(Debug)]
pub struct Parser<'t> {
    lexer: Lexer<'t>,
    token: Result<Option<SpToken>>,
}

impl<'t> From<&'t str> for Parser<'t> {
    fn from(text: &'t str) -> Self {
        Parser::new(Lexer::new(text))
    }
}

impl<'t> Parser<'t> {
    pub fn new(mut lexer: Lexer<'t>) -> Self {
        let token = lexer.next();
        Self { lexer, token }
    }

    pub fn is_eof(&self) -> bool {
        self.lexer.is_eof()
    }

    fn peek(&self) -> Result<Option<SpToken>> {
        self.token.clone()
    }

    fn adv(&mut self) -> Result<Option<SpToken>> {
        let next = self.lexer.next();
        std::mem::replace(&mut self.token, next)
    }

    /// Checks if the next token is part of the list, returning it if so.
    fn expect_any_token(&mut self, expected: &[Token]) -> Result<SpToken> {
        let token = self.peek()?;

        match (token, expected) {
            // Token matches
            (Some(token), expected) if expected.contains(token.inner()) => {
                self.adv()?;
                Ok(token)
            }

            // Token does not match, only one token expected
            (token, &[expected]) => {
                // get the string version of whether this is a token or EOF
                let got = token
                    .map(|t| format!("{} token", t.inner().name()))
                    .unwrap_or_else(|| "EOF".to_string());
                Err(SyntaxError::ExpectedGot {
                    expected: format!("{} token", expected.name()),
                    got,
                })
            }

            // Token does not match, any of N tokens expected
            (token, expected) => {
                // make the comma-separated list of everything except for the last item
                let expected_str = expected
                    .iter()
                    .take(expected.len() - 1)
                    .map(Token::name)
                    .collect::<Vec<_>>()
                    .join(", ");
                // get the string version of whether this is a token or EOF
                let got = token
                    .map(|t| format!("{} token", t.inner().name()))
                    .unwrap_or_else(|| "EOF".to_string());
                Err(SyntaxError::ExpectedGot {
                    expected: format!(
                        "{} or {} token",
                        expected_str,
                        expected.last().unwrap().name()
                    ),
                    got,
                })
            }
        }
    }

    /// Gets all expressions until EOF is reached, or until a quote end is reached.
    pub fn next_expr_list(&mut self) -> Result<Vec<SpExpr>> {
        let mut exprs = Vec::new();
        while let Some(peek) = self.peek()? {
            match peek.inner() {
                Token::RQuote => break,
                _ => exprs.push(self.next_expr()?),
            }
        }
        Ok(exprs)
    }

    pub fn next_expr(&mut self) -> Result<SpExpr> {
        // peek ahead and see if we need to handle a quote
        match self.peek()? {
            Some(peek) if *peek.inner() == Token::LQuote => self.next_quote(),
            _ => {
                let atom = self.next_atom()?;
                let span = atom.span();
                Ok(SpExpr::new(span, Expr::Atom(atom)))
            }
        }
    }

    pub fn next_quote(&mut self) -> Result<SpExpr> {
        let start = self.expect_any_token(&[Token::LQuote])?;
        let exprs = self.next_expr_list()?;
        let end = self.expect_any_token(&[Token::RQuote])?;
        let span = start.span().union(end.span());
        Ok(SpExpr::new(span, Expr::Quote(exprs)))
    }

    pub fn next_atom(&mut self) -> Result<SpAtom> {
        use Token::*;
        let token = self.expect_any_token(&[Word, Float, Int, Str])?;
        Ok(self.token_to_atom(token))
    }

    fn token_to_atom(&self, token: SpToken) -> SpAtom {
        // NOTE - self is required for this because we get the text
        let (span, token) = token.into_split();
        let text = span.text_at(self.lexer.text());
        let atom = match token {
            Token::Word => Atom::Word(text.to_string()),
            Token::Float => Atom::Float(text.parse().unwrap()),
            Token::Int => Atom::Int(text.parse().unwrap()),
            Token::Str => Atom::Str(unescape_string(text)),
            _ => panic!("invalid token specified for token_to_atom, it should be an atom"),
        };
        SpAtom::new(span, atom)
    }
}

fn unescape_string(text: &str) -> String {
    let mut string = String::with_capacity(text.len() - 2);
    let mut chars = text.chars().skip(1).take(text.len() - 2);
    while let Some(c) = chars.next() {
        if c == '\\' {
            let c = match chars
                .next()
                .expect("reached end of string literal before escape")
            {
                '"' => '"',
                '\'' => '\'',
                '\\' => '\\',
                'n' => '\n',
                'r' => '\r',
                't' => '\t',
                u => panic!(
                    "unexpected character escape that made it through the lexer: {:?}",
                    u
                ),
            };
            string.push(c);
        } else {
            string.push(c);
        }
    }
    string
}

// /////////////////////////////////////////////////////////////////////////////
// Tests
// /////////////////////////////////////////////////////////////////////////////

#[cfg(test)]
macro_rules! expect_atom {
    ($parser:expr, $expected:expr) => {{
        let expr_result = $parser.next_expr();
        assert!(
            expr_result.is_ok(),
            "expected {:?} but got {:?} instead",
            $expected,
            expr_result
        );
        let expr = expr_result.unwrap();
        let (span, expr) = expr.into_split();
        assert_eq!(expr, Expr::Atom(SpAtom::new(span, $expected)));
    }};
}

#[cfg(test)]
macro_rules! expect_expr {
    ($parser:expr, $expected:expr) => {{
        let expr_result = $parser.next_expr();
        assert!(
            expr_result.is_ok(),
            "expected {:?} but got {:?} instead",
            $expected,
            expr_result
        );
        let expr = expr_result.unwrap();
        assert_eq!(expr, $expected);
    }};
}

/// Makes an SpExpr Quote value using the given SpExpr values
#[cfg(test)]
macro_rules! make_quote {
    ($($expr:expr),+ $(,)?) => {{
        SpExpr::new(
            Default::default(),
            Expr::Quote(make_quote_vec!($($expr),+))
        )
    }};
}

/// Makes a vec appropriate for an Expr::Quote
#[cfg(test)]
macro_rules! make_quote_vec {
    ($($expr:expr),+ $(,)?) => {{
        vec![$(
            SpExpr::new(Default::default(), $expr)
        ),+]
    }};
}

/// Makes an SpAtom from an Atom type.
#[cfg(test)]
macro_rules! make_atom {
    ($atom:expr) => {{
        SpAtom::new(Default::default(), $atom)
    }};
}

#[test]
fn test_parser_atoms() {
    let mut parser = Parser::from(
        r#"
    a ab bcd dcefg foo bar baz
    1 2 3 4 5
    1.2 3.4 5.6 7.8 9.10
    "this is a string"
    "this\nis\na\nstring\nwith\nnewlines"
    "this\tis\ta\tstring\twith\ttabs"
    "#,
    );
    expect_atom!(parser, Atom::Word("a".to_string()));
    expect_atom!(parser, Atom::Word("ab".to_string()));
    expect_atom!(parser, Atom::Word("bcd".to_string()));
    expect_atom!(parser, Atom::Word("dcefg".to_string()));
    expect_atom!(parser, Atom::Word("foo".to_string()));
    expect_atom!(parser, Atom::Word("bar".to_string()));
    expect_atom!(parser, Atom::Word("baz".to_string()));
    expect_atom!(parser, Atom::Int(1));
    expect_atom!(parser, Atom::Int(2));
    expect_atom!(parser, Atom::Int(3));
    expect_atom!(parser, Atom::Int(4));
    expect_atom!(parser, Atom::Int(5));
    expect_atom!(parser, Atom::Float(1.2));
    expect_atom!(parser, Atom::Float(3.4));
    expect_atom!(parser, Atom::Float(5.6));
    expect_atom!(parser, Atom::Float(7.8));
    expect_atom!(parser, Atom::Float(9.1));
    expect_atom!(parser, Atom::Str("this is a string".to_string()));
    expect_atom!(
        parser,
        Atom::Str("this\nis\na\nstring\nwith\nnewlines".to_string())
    );
    expect_atom!(
        parser,
        Atom::Str("this\tis\ta\tstring\twith\ttabs".to_string())
    );
    assert!(parser.is_eof());
}

#[test]
fn test_parser_quotes() {
    let mut parser = Parser::from(
        r#"
        [
            a ab bcd dcefg foo bar baz
        ]
        [1 2 3 4 5
            [1.2 3.4 5.6 7.8 9.10]
        ]
        "#,
    );

    expect_expr!(
        parser,
        make_quote![
            Expr::Atom(make_atom!(Atom::Word("a".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("ab".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("bcd".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("dcefg".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("foo".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("bar".to_string()))),
            Expr::Atom(make_atom!(Atom::Word("baz".to_string()))),
        ]
    );

    expect_expr!(
        parser,
        make_quote![
            Expr::Atom(make_atom!(Atom::Int(1))),
            Expr::Atom(make_atom!(Atom::Int(2))),
            Expr::Atom(make_atom!(Atom::Int(3))),
            Expr::Atom(make_atom!(Atom::Int(4))),
            Expr::Atom(make_atom!(Atom::Int(5))),
            Expr::Quote(make_quote_vec![
                Expr::Atom(make_atom!(Atom::Float(1.2))),
                Expr::Atom(make_atom!(Atom::Float(3.4))),
                Expr::Atom(make_atom!(Atom::Float(5.6))),
                Expr::Atom(make_atom!(Atom::Float(7.8))),
                Expr::Atom(make_atom!(Atom::Float(9.10))),
            ]),
        ]
    );
}