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use rand::prelude::*;
use std::{error::Error, fmt::Debug};

pub trait RandomVariable: Clone + Debug + PartialEq {}
impl<T> RandomVariable for T where T: Clone + Debug + PartialEq {}

#[derive(thiserror::Error, Debug)]
pub enum DistributionError {
    #[error("params are not set")]
    ParamsAreNotSet,
}

/// # Distribution
/// ![tex](https://latex.codecogs.com/svg.latex?p%28x%7C\mathbf{\theta}%29)
pub trait Distribution {
    type T: RandomVariable;
    type U: RandomVariable;

    fn p(&self, x: &Self::T, theta: &Self::U) -> Result<f64, Box<dyn Error>>;
    fn ln_p(&self, x: &Self::T, theta: &Self::U) -> Result<f64, Box<dyn Error>> {
        Ok(self.p(x, theta)?.ln())
    }
    fn sample(&self, theta: &Self::U, rng: &mut StdRng) -> Result<Self::T, Box<dyn Error>>;
}