Cleaned up atoms

- Atoms now use MFBI to distinguish between thin and owned atoms.
- Introduced TryFromExpr and ToExpr (formerly ToClause) from the old FFI
- Standardized on Bottom being a ProjErr, which means that there will be no RTErr

orchid-extension/src/conv.rs

@@ -0,0 +1,55 @@
+use orchid_base::location::Pos;
+
+use crate::{atom::{AtomicFeatures, TypAtom}, error::{ProjectError, ProjectResult}, expr::{atom, bot_obj, ExprHandle, GenExpr, OwnedExpr}, system::downcast_atom};
+
+pub trait TryFromExpr: Sized {
+  fn try_from_expr(expr: ExprHandle) -> ProjectResult<Self>;
+}
+
+impl TryFromExpr for OwnedExpr {
+  fn try_from_expr(expr: ExprHandle) -> ProjectResult<Self> { Ok(OwnedExpr::new(expr)) }
+}
+
+impl<T: TryFromExpr, U: TryFromExpr> TryFromExpr for (T, U) {
+  fn try_from_expr(expr: ExprHandle) -> ProjectResult<Self> {
+    Ok((T::try_from_expr(expr.clone())?, U::try_from_expr(expr)?))
+  }
+}
+
+pub struct ErrorNotAtom(Pos);
+impl ProjectError for ErrorNotAtom {
+  const DESCRIPTION: &'static str = "Expected an atom";
+  fn one_position(&self) -> Pos { self.0.clone() }
+}
+
+pub struct ErrorUnexpectedType(Pos);
+impl ProjectError for ErrorUnexpectedType {
+  const DESCRIPTION: &'static str = "Type error";
+  fn one_position(&self) -> Pos {
+      self.0.clone()
+  }
+}
+
+impl<A: AtomicFeatures> TryFromExpr for TypAtom<A> {
+  fn try_from_expr(expr: ExprHandle) -> ProjectResult<Self> {
+    OwnedExpr::new(expr).foreign_atom().map_err(|ex| ErrorNotAtom(ex.pos.clone()).pack())
+      .and_then(|f| downcast_atom(f).map_err(|f| ErrorUnexpectedType(f.pos).pack()))
+  }
+}
+
+pub trait ToExpr {
+  fn to_expr(self) -> GenExpr;
+}
+
+impl<T: ToExpr> ToExpr for ProjectResult<T> {
+  fn to_expr(self) -> GenExpr {
+      match self {
+        Err(e) => bot_obj(e),
+        Ok(t) => t.to_expr(),
+      }
+  }
+}
+
+impl<A: AtomicFeatures> ToExpr for A {
+  fn to_expr(self) -> GenExpr { atom(self) }
+}