use std::fmt;

#[derive(Debug, Copy, Clone, PartialEq, Eq)]
pub enum Position {
    At(usize),
    End,
}

impl fmt::Display for Position {
    fn fmt(&self, f: &mut fmt::Formatter) -> fmt::Result {
        match self {
            Position::At(index) => write!(f, "on position {}", index),
            Position::End => write!(f, "at the end"),
        }
    }
}

pub trait Error: std::error::Error {
    fn open_parenthesis_expected(position: Position) -> Self;
    fn close_parenthesis_expected(position: Position) -> Self;
    fn close_parenthesis_unexpected(position: Position) -> Self;
    fn lambda_expected(position: Position) -> Self;
    fn dot_expected(position: Position) -> Self;
    fn dot_unexpected(position: Position) -> Self;
    fn token_unexpected(position: Position) -> Self;
    fn parameter_expected(position: Position) -> Self;
    fn end_expected(position: Position) -> Self;
    fn end_unexpected(position: Position) -> Self;
    fn unbound_variable(identifier: String, position: Position) -> Self;
    fn no_expression(position: Position) -> Self;
}