wisp/src/syntax/ast.rs

use ordered_float::OrderedFloat;
use std::{
    borrow::Cow,
    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<'a> {
    List(Vec<Spanned<Self>>),
    Vector(Vec<Spanned<Self>>),
    Map(Vec<(Spanned<Self>, Spanned<Self>)>),
    Quote(Box<Spanned<Self>>),
    Symbol(Cow<'a, str>),
    Keyword(Cow<'a, str>),
    Number(OrderedFloat<f64>),
    String(Cow<'a, str>),
}

impl<'a> Display for Expr<'a> {
    fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
        match self {
            Self::List(list) => write_seq(f, list, "(", ")"),
            Self::Vector(vec) => write_seq(f, vec, "[", "]"),
            Self::Map(map) => write_seq(f, map.iter().map(|(k, v)| format!("{k} {v}")), "{", "}"),
            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 write_seq(
    f: &mut impl Write,
    iterable: impl IntoIterator<Item = impl Display>,
    delimiter_left: &str,
    delimiter_right: &str,
) -> std::fmt::Result {
    let mut iter = iterable.into_iter();
    write!(f, "{delimiter_left}")?;
    if let Some(x) = iter.next() {
        write!(f, "{x}")?;
    }
    for x in iter {
        write!(f, " {x}")?;
    }
    write!(f, "{delimiter_right}")
}