pub mod step;
pub mod util;
pub mod subst;

/// A leaf node for S-Expressions.
///
/// May represent built-in operators,
/// variables, functions (to be added) or values.
#[derive(Debug)]
#[derive(PartialEq)]
#[derive(Clone)]
pub enum SLeaf {
    Add,
    Sub,
    Mul,
    Div,
    Int(i32),
    Var(String),
}

/// An S-Expression; the defining structure of the language.
///
/// This structure is not intended to correspond with
/// IETF-standardized s-expressions; they are only inspiration.
#[derive(Debug)]
#[derive(PartialEq)]
#[derive(Clone)]
pub enum SExp {
    SCons(Box<SExp>, Box<SExp>),
    Atom(SLeaf),
}