#[derive(Debug)]
pub struct WithLocation<T> {
    value: T,
    location: (usize, usize),
}

impl<T> WithLocation<T> {
    pub fn new(value: T, start: usize, end: usize) -> WithLocation<T> {
        WithLocation {
            value: value,
            location: (start, end),
        }
    }

    pub fn map<U, F: FnOnce(T) -> U>(self, f: F) -> WithLocation<U> {
        WithLocation {
            value: f(self.value),
            location: self.location,
        }
    }

    pub fn join_map<U, V, F>(self, other: WithLocation<U>, f: F) -> WithLocation<V>
        where F: FnOnce(WithLocation<T>, WithLocation<U>) -> V
    {
        let loc1 = self.location;
        let loc2 = other.location;
        WithLocation {
            value: f(self, other),
            location: (loc1.0, loc2.1),
        }
    }
}

#[derive(Debug)]
pub struct Program(pub Box<WithLocation<Expression>>);

#[derive(Debug)]
pub enum UnaryOp {
    Pos,
    Neg,
    Not,
}

#[derive(Debug)]
pub enum BinOp {
    Add,
    Sub,
    Mul,
    Div,
    FloorDiv,
    Eq,
    Neq,
    Gt,
    Lt,
    Ge,
    Le,
    And,
    Or,
}

#[derive(Debug)]
pub enum Expression {
    UnaryOp(UnaryOp, Box<WithLocation<Expression>>),
    BinOp(BinOp, Box<WithLocation<Expression>>, Box<WithLocation<Expression>>),
    Number(u64),
    String(String),
    Nil,
}