[fine] Oh no a runtime and module loading and stuff

Lots of test work to use the new mechanism. I'm not sure I like it.

fine/src/semantics.rs

@@ -3,7 +3,12 @@ use crate::{
     tokens::{Lines, Token, TokenKind},
     vm::StackValue,
 };
-use std::{cell::RefCell, collections::HashMap, fmt, rc::Rc};
+use std::{
+    cell::{OnceCell, RefCell},
+    collections::HashMap,
+    fmt,
+    rc::{Rc, Weak},
+};
 
 // TODO: Unused variables?
 // TODO: Underscore for discard?
@@ -610,6 +615,8 @@ pub struct Semantics {
     syntax_tree: Rc<SyntaxTree>,
     lines: Rc<Lines>,
 
+    import_map: OnceCell<HashMap<String, Weak<Semantics>>>,
+
     // Instead of physical parents, this is the set of *logical* parents.
     // This is what is used for binding.
     logical_parents: Vec<Option<TreeRef>>,
@@ -635,6 +642,7 @@ impl Semantics {
             source,
             syntax_tree: tree.clone(),
             lines,
+            import_map: OnceCell::new(),
             logical_parents,
             errors: RefCell::new(vec![]),
             types: RefCell::new(vec![Incremental::None; tree.len()]),
@@ -653,6 +661,10 @@ impl Semantics {
         semantics
     }
 
+    pub fn set_imports(&self, imports: HashMap<String, Weak<Semantics>>) {
+        self.import_map.set(imports).expect("imports already set");
+    }
+
     pub fn source(&self) -> Rc<str> {
         self.source.clone()
     }
@@ -665,6 +677,10 @@ impl Semantics {
         self.lines.clone()
     }
 
+    pub fn imports(&self) -> Vec<String> {
+        vec![]
+    }
+
     pub fn snapshot_errors(&self) -> Vec<Error> {
         let mut result = (*self.errors.borrow()).clone();
         result.sort_by(|a, b| match a.start.0.cmp(&b.start.0) {