Most files suffered major changes

- Less ambiguous syntax
- Better parser (Chumsky only does tokenization now)
- Tidy(|ier) error handling
- Facade for simplified embedding
- External code grouped in (fairly) self-contained Systems
- Dynamic action dispatch
- Many STL additions

src/systems/stl/panic.rs

@@ -0,0 +1,26 @@
+use std::fmt::Display;
+
+use crate::foreign::ExternError;
+use crate::systems::cast_exprinst::with_str;
+use crate::{define_fn, ConstTree, Interner};
+
+/// An unrecoverable error in Orchid land. Because Orchid is lazy, this only
+/// invalidates expressions that reference the one that generated it.
+pub struct OrchidPanic(String);
+
+impl Display for OrchidPanic {
+  fn fmt(&self, f: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
+    write!(f, "Orchid code panicked: {}", self.0)
+  }
+}
+
+impl ExternError for OrchidPanic {}
+
+define_fn! {
+  /// Takes a message, returns an [ExternError] unconditionally.
+  Panic = |x| with_str(x, |s| Err(OrchidPanic(s.clone()).into_extern()))
+}
+
+pub fn panic(i: &Interner) -> ConstTree {
+  ConstTree::tree([(i.i("panic"), ConstTree::xfn(Panic))])
+}