Updated macro system to process and return mactree and then lower it separately to gexpr

orchid-std/src/macros/lower.rs

@@ -0,0 +1,80 @@
+use std::collections::VecDeque;
+
+use async_fn_stream::stream;
+use futures::{FutureExt, StreamExt, stream};
+use itertools::Itertools;
+use orchid_base::{OrcErrv, Paren, Sym, fmt, is, mk_errv, report};
+use orchid_extension::ToExpr;
+use orchid_extension::gen_expr::{GExpr, GExprKind, bot, call};
+use substack::Substack;
+
+use crate::macros::mactree::MacTreeSeq;
+use crate::{MacTok, MacTree};
+
+fn on_err(e: OrcErrv) -> GExpr {
+	report(e.clone());
+	bot(e)
+}
+
+pub async fn lower(mt: &MacTree, args: Substack<'_, Sym>) -> GExpr {
+	match mt.tok() {
+		MacTok::Bottom(b) => on_err(b.clone()),
+		MacTok::Slot => on_err(mk_errv(
+			is("Lowering intermediary slotted mactree").await,
+			"Found a Slot during lowering, which should only exist in temporary templates",
+			[mt.pos()],
+		)),
+		MacTok::Ph(ph) => on_err(mk_errv(
+			is("Lowering placeholder").await,
+			format!("Found {ph} during lowering. Placeholders should only exist in macro patterns"),
+			[mt.pos()],
+		)),
+		MacTok::S(Paren::Curly | Paren::Square, _) => on_err(mk_errv(
+			is("Lowering {...} or [...]").await,
+			format!("Cannot lower this syntax, probable incorrect macro call: {}", fmt(mt).await),
+			[mt.pos()],
+		)),
+		MacTok::S(Paren::Round, b) if b.items.is_empty() => on_err(mk_errv(
+			is("Cannot lower empty ()").await,
+			"Attempted to lower empty (). All expressions must have a value.",
+			[mt.pos()],
+		)),
+		MacTok::Lambda(arg, body) => {
+			let MacTok::Name(n) = arg.tok() else {
+				return on_err(mk_errv(
+					is("Lowering lambda with complex param").await,
+					format!("In code after macros, lambda params can only be names, not {}", fmt(arg).await),
+					[arg.pos()],
+				));
+			};
+			if body.items.is_empty() {
+				return on_err(mk_errv(
+					is("Lowering lambda with empty body").await,
+					"Lambdas without a body are invalid, all expressions in Orchid must have a value",
+					[mt.pos()],
+				));
+			}
+			let body = lower_seq(body, args.push(n.clone())).await;
+			GExprKind::Lambda(Box::new(body)).at(mt.pos())
+		},
+		MacTok::S(Paren::Round, body) => lower_seq(body, args).await,
+		MacTok::Name(n) => match args.iter().find_position(|b| *b == n) {
+			Some((i, _)) => GExprKind::Arg(i.try_into().unwrap()).at(mt.pos()),
+			None => n.clone().to_gen().await,
+		},
+		MacTok::Value(expr) => expr.clone().to_gen().await,
+	}
+}
+
+pub async fn lower_seq(mtv: &MacTreeSeq, args: Substack<'_, Sym>) -> GExpr {
+	let mut exprs = stream(async |mut h| {
+		for mt in mtv.items.iter() {
+			h.emit(lower(mt, args.clone()).await).await
+		}
+	})
+	.collect::<VecDeque<_>>()
+	.boxed_local()
+	.await;
+	let first = exprs.pop_front().expect("We checked first that it isn't empty");
+	stream::iter(exprs).fold(first, async |f, x| call(f, x).await).await
+}