crftng-intrprtrs/src/ast/parser.rs

use super::astnode;
use super::astnode::{ASTNode, BinaryExpr};
use crate::lexer::{token, token::TokenType};
use std::iter;
use std::result::Result as StdResult;

type Result<T> = StdResult<T, ASTParsingError>;

#[derive(Debug)]
pub enum ASTParsingError {
	UnmatchedBrace,
}

impl std::fmt::Display for ASTParsingError {
	fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
		match *self {
			Self::UnmatchedBrace => write!(f, "Unmatched brace"),
		}
	}
}
impl std::error::Error for ASTParsingError {}

pub struct Parser<'a, T: Iterator<Item = token::Token<'a>>> {
	token_iter: iter::Peekable<T>,
}

impl<'a, T: Iterator<Item = token::Token<'a>>> Parser<'a, T> {
	pub fn new(iter: T) -> Parser<'a, T> {
		Parser {
			token_iter: iter.peekable(),
		}
	}
	pub fn scan_expressions(&mut self) -> StdResult<Vec<ASTNode>, Vec<ASTParsingError>> {
		let mut tokens = Vec::new();
		let mut errors = Vec::new();

		while self.token_iter.peek().is_some() {
			match self.expression() {
				Ok(token) => {
					if errors.is_empty() {
						tokens.push(token)
					}
				}
				Err(e) => errors.push(e),
			}
		}
		if errors.is_empty() {
			Ok(tokens)
		} else {
			Err(errors)
		}
	}

	fn expression(&mut self) -> Result<ASTNode> {
		self.equality()
	}

	fn equality(&mut self) -> Result<ASTNode> {
		let mut node = self.comparison()?;
		while let Some(o) = self
			.token_iter
			.next_if(|t| matches!(t.token_type, TokenType::EqualEqual | TokenType::BangEqual))
		{
			node = BinaryExpr::new(
				Box::new(node),
				o.token_type.try_into().unwrap(),
				Box::new(self.comparison()?),
			)
			.into();
		}
		Ok(node)
	}

	fn comparison(&mut self) -> Result<ASTNode> {
		let mut node = self.term()?;

		while let Some(o) = self.token_iter.next_if(|t| {
			matches!(
				t.token_type,
				TokenType::Greater
					| TokenType::GreaterEqual
					| TokenType::Less | TokenType::LessEqual
			)
		}) {
			node = BinaryExpr::new(
				Box::new(node),
				o.token_type.try_into().unwrap(),
				Box::new(self.comparison()?),
			)
			.into();
		}
		Ok(node)
	}

	fn term(&mut self) -> Result<ASTNode> {
		let mut node = self.factor()?;

		while let Some(o) = self
			.token_iter
			.next_if(|t| matches!(t.token_type, TokenType::Minus | TokenType::Plus))
		{
			node = BinaryExpr::new(
				Box::new(node),
				o.token_type.try_into().unwrap(),
				Box::new(self.comparison()?),
			)
			.into()
		}
		Ok(node)
	}

	fn factor(&mut self) -> Result<ASTNode> {
		let mut node = self.unary()?;

		while let Some(o) = self
			.token_iter
			.next_if(|t| matches!(t.token_type, TokenType::Star | TokenType::Slash))
		{
			node = BinaryExpr::new(
				Box::new(node),
				o.token_type.try_into().unwrap(),
				Box::new(self.comparison()?),
			)
			.into();
		}
		Ok(node)
	}

	fn unary(&mut self) -> Result<ASTNode> {
		if let Some(op) = self
			.token_iter
			.next_if(|t| matches!(t.token_type, TokenType::Bang | TokenType::Minus))
		{
			let right = Box::new(self.unary()?);
			Ok(ASTNode::UnaryExpr(astnode::UnaryExpr::new(
				op.token_type.try_into().unwrap(),
				right,
			)))
		} else {
			self.primary()
		}
	}

	fn primary(&mut self) -> Result<ASTNode> {
		let node = match self.token_iter.next().map(|it| it.token_type) {
			Some(TokenType::False) => ASTNode::Literal(astnode::Literal::Bool(false)),
			Some(TokenType::True) => ASTNode::Literal(astnode::Literal::Bool(true)),
			Some(TokenType::Int(i)) => ASTNode::Literal(astnode::Literal::Int(i)),
			Some(TokenType::String(i)) => ASTNode::Literal(astnode::Literal::String(i)),
			Some(TokenType::Float(f)) => ASTNode::Literal(astnode::Literal::Float(f)),
			Some(TokenType::LeftParen) => {
				let expr = self.expression()?;
				let group = astnode::GroupingExpr::new(Box::new(expr));
				match self
					.token_iter
					.next_if(|v| matches!(v.token_type, TokenType::RightParen))
				{
					Some(_) => return Ok(group.into()),
					None => return Err(ASTParsingError::UnmatchedBrace),
				}
			}
			Some(a) => panic!("{:#?}", a),
			None => todo!(),
		};
		Ok(node)
	}
}