wisp/src/syntax/ast.rs

use ordered_float::OrderedFloat;
use std::{
    fmt::{Display, Write},
    hash::Hash,
};

pub type Span = std::ops::Range<usize>;

/// A spanned item
#[derive(Clone, Debug)]
pub struct Spanned<T> {
    pub item: T,
    pub span: Span,
}

impl<T> Spanned<T> {
    pub fn new(item: T, span: Span) -> Self {
        Self { item, span }
    }
}

impl<T: Display> Display for Spanned<T> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        write!(f, "{} \x1B[2m@ {:?}\x1B[22m", self.item, self.span)
    }
}

impl<T: PartialEq> PartialEq for Spanned<T> {
    fn eq(&self, other: &Self) -> bool {
        self.item == other.item
    }
}

impl<T: Hash> Hash for Spanned<T> {
    fn hash<H: std::hash::Hasher>(&self, state: &mut H) {
        self.item.hash(state);
    }
}

/// A Wisp AST
#[derive(Debug, Clone, Hash, PartialEq)]
pub enum Expr<'s> {
    List(Vec<Spanned<Self>>),
    Vector(Vec<Spanned<Self>>),
    Pair((Box<Spanned<Self>>, Box<Spanned<Self>>)),
    Quote(Box<Spanned<Self>>),
    Symbol(&'s str),
    Keyword(&'s str),
    Number(OrderedFloat<f64>),
    String(&'s str),
}

impl<'s> Display for Expr<'s> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::List(list) => fmt_list(f, list),
            Self::Vector(vec) => {
                write!(f, "#")?;
                fmt_list(f, vec)
            }
            Self::Pair((l, r)) => write!(f, "{l} . {r}"),
            Self::Quote(expr) => write!(f, "'{expr}"),
            Self::Symbol(sym) => write!(f, "{sym}"),
            Self::Keyword(kw) => write!(f, ":{kw}"),
            Self::Number(n) => write!(f, "{n}"),
            Self::String(s) => write!(f, "\"{s}\""),
        }
    }
}

fn fmt_list(f: &mut impl Write, iterable: &[Spanned<Expr>]) -> std::fmt::Result {
    let mut iter = iterable.iter();
    write!(f, "(")?;
    if let Some(i) = iter.next() {
        write!(f, "{i}")?;
    }
    for i in iter {
        write!(f, " {i}")?;
    }
    write!(f, ")")
}