deriv/src/binding.rs

use crate::token::Token;
use crate::expression::Expression;

#[derive(Copy, Clone, Debug, PartialEq)]
pub enum Associativity {
	Left,
	Right,
	Full,
}

#[derive(Copy, Clone, Debug, PartialEq, PartialOrd)]
pub enum Power {
	Minimum,
	Addition,
	Multiplication,
	Exponentiation,
	Maximum,
}

#[derive(Copy, Clone, Debug)]
pub struct Binding {
	power: Power,
	associativity: Associativity,
}

impl Binding {
	pub fn left(power: Power) -> Self {
		Self { power, associativity: Associativity::Left }
	}

	pub fn right(power: Power) -> Self {
		Self { power, associativity: Associativity::Right }
	}

	pub fn full(power: Power) -> Self {
		Self { power, associativity: Associativity::Full }
	}

	pub fn of_operator(token: &Token) -> Self {
		if token.starts_expression() {
			Binding::full(Power::Multiplication)
		} else {
			match token {
				Token::Plus => Binding::full(Power::Addition),
				Token::Minus => Binding::left(Power::Addition),
				Token::Times => Binding::full(Power::Multiplication),
				Token::Divide => Binding::left(Power::Multiplication),
				Token::Caret => Binding::right(Power::Exponentiation),
				Token::CloseParen => Binding::left(Power::Minimum),
				_ => unreachable!(),
			}
		}
	}


	pub fn of_expression(expr: &Expression) -> Self {
		match expr {
			Expression::Sum(_, _) => Self::full(Power::Addition),
			Expression::Difference(_, _) => Self::left(Power::Addition),
			Expression::Product(_, _) => Self::full(Power::Multiplication),
			Expression::Quotient(_, _) => Self::left(Power::Multiplication),
			Expression::Exponent(_, _) => Self::right(Power::Exponentiation),
			Expression::Integer(_) => Self::left(Power::Maximum),
			Expression::Symbol(_) => Self::left(Power::Maximum),
		}
	}
}

impl std::cmp::PartialEq for Binding {
	fn eq(&self, other: &Self) -> bool
	{
		self.associativity == Associativity::Full
			&& self.power == other.power
	}
}

impl std::cmp::PartialOrd for Binding {
	fn partial_cmp(&self, rhs: &Self) -> Option<std::cmp::Ordering>
	{
		Some(if self.power < rhs.power {
			std::cmp::Ordering::Less
		} else if self.power > rhs.power {
			std::cmp::Ordering::Greater
		} else {
			match self.associativity {
				Associativity::Left => std::cmp::Ordering::Less,
				Associativity::Right => std::cmp::Ordering::Greater,
				Associativity::Full => std::cmp::Ordering::Equal,
			}
		})
	}
}

#[cfg(test)]
mod tests {
	use super::*;

	#[test]
	fn left_assoc_min_is_less_than_left_assoc_add() {
		assert_eq!(
			Binding::left(Power::Minimum).partial_cmp(
				&Binding::left(Power::Addition)),
			Some(std::cmp::Ordering::Less));
	}

	#[test]
	fn left_assoc_add_is_less_than_left_assoc_add() {
		assert_eq!(
			Binding::left(Power::Addition).partial_cmp(
				&Binding::left(Power::Addition)),
			Some(std::cmp::Ordering::Less));
	}

	#[test]
	fn left_assoc_mult_is_greater_than_left_assoc_add() {
		assert_eq!(
			Binding::left(Power::Multiplication).partial_cmp(
				&Binding::left(Power::Addition)),
			Some(std::cmp::Ordering::Greater));
	}

	#[test]
	fn right_assoc_min_is_less_than_right_assoc_add() {
		assert_eq!(
			Binding::right(Power::Minimum).partial_cmp(
				&Binding::right(Power::Addition)),
			Some(std::cmp::Ordering::Less));
	}

	#[test]
	fn right_assoc_add_is_greater_than_right_assoc_add() {
		assert_eq!(
			Binding::right(Power::Addition).partial_cmp(
				&Binding::right(Power::Addition)),
			Some(std::cmp::Ordering::Greater));
	}

	#[test]
	fn right_assoc_mul_is_greater_than_right_assoc_add() {
		assert_eq!(
			Binding::right(Power::Multiplication).partial_cmp(
				&Binding::right(Power::Addition)),
			Some(std::cmp::Ordering::Greater));
	}

	#[test]
	fn full_assoc_min_is_less_than_full_assoc_add() {
		assert_eq!(
			Binding::full(Power::Minimum).partial_cmp(
				&Binding::full(Power::Addition)),
			Some(std::cmp::Ordering::Less));
	}

	#[test]
	fn full_assoc_add_is_equal_to_full_assoc_add() {
		assert_eq!(
			Binding::full(Power::Addition).partial_cmp(
				&Binding::full(Power::Addition)),
			Some(std::cmp::Ordering::Equal));
	}

	#[test]
	fn full_assoc_mul_is_greater_than_full_assoc_add() {
		assert_eq!(
			Binding::full(Power::Multiplication).partial_cmp(
				&Binding::full(Power::Addition)),
			Some(std::cmp::Ordering::Greater));
	}

	#[test]
	fn left_assoc_min_is_not_equal_to_left_assoc_min() {
		assert_ne!(
			Binding::left(Power::Minimum), Binding::left(Power::Minimum));
	}

	#[test]
	fn right_assoc_min_is_not_equal_to_right_assoc_min() {
		assert_ne!(
			Binding::right(Power::Minimum), Binding::right(Power::Minimum));
	}

	#[test]
	fn full_assoc_min_is_equal_to_full_assoc_min() {
		assert_eq!(
			Binding::full(Power::Minimum), Binding::left(Power::Minimum));
	}
}