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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),
Quote,
Nil,
}
/// 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),
}
use SExp::*;
use SLeaf::*;
impl SExp {
pub fn is_value(&self) -> bool {
match self {
SCons(a, _) => **a == Atom(Quote),
Atom(Var(_)) => false,
Atom(_) => true,
}
}
pub fn consists_of_values(&self) -> bool {
self.is_value() || match self {
SCons(a, b) if (*a).is_value() => b.consists_of_values(),
_ => false
}
}
}
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