Amo/src/parser/mod.rs

//! Tools to convert a stream of tokens into a parse tree
//!
//! Parsing is the stage that follows lexing, wherein a linear stream of tokens is
//! converted into a tree structure that reflects the syntax of the language.  This is
//! also where syntax errors are caught.
//!
//! amo uses a push-based parsing system, where state is represented using a
//! [`PartialTree`], which can [`accept()`](PartialTree::accept) new tokens, producing a
//! new state.
//!
//! The root of the parser is typically [`crate::parser::program`].

use std::{ops::Range, mem::{Discriminant, self}};

use logos::Lexer;

use crate::{token::{Token, InfixRank1, InfixRank6, InfixRank5, InfixRank3, InfixRank2, InfixRank4}, cons};
use std::mem::discriminant;

pub mod program;
pub mod declaration;
pub mod expr;
pub mod pattern;
pub mod infix;

pub trait Parsable: Sized {
	fn expected() -> (Vec<Discriminant<Token>>, bool);
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError>;
	fn matches(l: &Token) -> bool {
		let (expected, can_zero_width) = Self::expected();
		can_zero_width || expected.contains(&discriminant(l))
	}
}

/// Information about a parsing error that happened somewhere
#[derive(Debug)]
pub struct ParseError {
	/// The span of the token that the parse error occured on
	pub location: Range<usize>,

	/// The specific error that occured, with more details
	pub expected: Vec<Discriminant<Token>>,
}

pub struct WrappedLexer<'a>(Lexer<'a, Token>, Token);

impl<'a> WrappedLexer<'a> {
	pub fn new(mut l: Lexer<'a, Token>) -> WrappedLexer {
		let token = l.next().unwrap_or(Token::EOF);
		WrappedLexer(l, token)
	}

	pub fn curtok(&self) -> &Token {
		&self.1
	}

	pub fn monch(&mut self) -> Token {
		let mut old = self.0.next().unwrap_or(Token::EOF);
		mem::swap(&mut old, &mut self.1);
		old
	}

	pub fn span(&self) -> Range<usize> {
		self.0.span()
	}
}

impl<P: Parsable> Parsable for Box<P> {
	fn expected() -> (Vec<Discriminant<Token>>, bool) {
		P::expected()
	}
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		P::parse(l).map(Box::new)
	}
}

impl<P: Parsable> Parsable for Option<P> {
	fn expected() -> (Vec<Discriminant<Token>>, bool) {
		(P::expected().0, true)
	}
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		if P::matches(l.curtok()) {
			P::parse(l).map(Some)
		} else {
			Ok(None)
		}
	}
}

impl<A: Parsable, B: Parsable> Parsable for (A, B) {
	fn expected() -> (Vec<Discriminant<Token>>, bool) {
		let (a_expct, a_zw) = A::expected();
		if a_zw {
			let (b_expct, b_zw) = B::expected();
			(
				a_expct.into_iter()
					.chain(b_expct.into_iter())
					.collect(),
				b_zw
			)
		} else {
			(a_expct, false)
		}
	}
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let a = A::parse(l)?;
		let b = B::parse(l)?;
		Ok((a, b))
	}
}

impl Parsable for String {
	fn expected() -> (Vec<Discriminant<Token>>, bool) {
		(vec![discriminant(&Token::Symbol("".to_owned()))], false)
	}
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
		match l.monch() {
			Token::Symbol(s) => Ok(s),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0,
			})
		}
	}
}

impl<P: Parsable> Parsable for Vec<P> {
	fn expected() -> (Vec<Discriminant<Token>>, bool) {
		(P::expected().0, true)
	}
	fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		vec_parse_inner(l, Vec::new())
	}
}

fn vec_parse_inner<P: Parsable>(l: &mut WrappedLexer, collected: Vec<P>) -> Result<Vec<P>,ParseError> {
	if P::matches(l.curtok()) {
		let new_element = P::parse(l)?;
		vec_parse_inner(l, cons(collected, new_element))
	} else {
		Ok(collected)
	}
}

pub fn parse_delineated_vec<P: Parsable>(l: &mut WrappedLexer, delineator: Discriminant<Token>) -> Result<Vec<P>, ParseError> {
	parse_delineated_vec_inner(l, delineator, Vec::new())
}
fn parse_delineated_vec_inner<P: Parsable>(l: &mut WrappedLexer, d: Discriminant<Token>, acc: Vec<P>) -> Result<Vec<P>, ParseError> {
	if P::matches(l.curtok()) {
		let acc = cons(acc, P::parse(l)?);
		if d == discriminant(l.curtok()) {
			l.monch();
			parse_delineated_vec_inner(l, d, acc)
		} else { Ok(acc) }
	} else { Ok(acc) }
}

pub fn absorb_token_or_error(l: &mut WrappedLexer, t: Discriminant<Token>) -> Result<Token, ParseError> {
	if discriminant(l.curtok()) == t {
		Ok(l.monch())
	} else {
		Err(ParseError {
			location: l.span(),
			expected: vec![t],
		})
	}
}

impl Parsable for InfixRank1 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R1Infix(InfixRank1::LOr))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R1Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}

impl Parsable for InfixRank2 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R2Infix(InfixRank2::LAnd))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R2Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}

impl Parsable for InfixRank3 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R3Infix(InfixRank3::Eq))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R3Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}

impl Parsable for InfixRank4 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R4Infix(InfixRank4::Range))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R4Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}

impl Parsable for InfixRank5 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R5Infix(InfixRank5::Add))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R5Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}

impl Parsable for InfixRank6 {
    fn expected() -> (Vec<Discriminant<Token>>, bool) {
        (vec![discriminant(&Token::R6Infix(InfixRank6::Mul))], false)
    }

    fn parse(l: &mut WrappedLexer) -> Result<Self, ParseError> {
		let span = l.span();
        match l.monch() {
			Token::R6Infix(o) => Ok(o),
			_ => Err(ParseError {
				location: span,
				expected: Self::expected().0
			}),
		}
    }
}