1 files changed, 109 insertions, 0 deletions
diff --git a/dhall/src/ctxt.rs b/dhall/src/ctxt.rs
new file mode 100644
index 0000000..1d97232
--- /dev/null
+++ b/dhall/src/ctxt.rs
@@ -0,0 +1,109 @@
+use elsa::vec::FrozenVec;
+use once_cell::sync::OnceCell;
+
+use crate::semantics::{Import, ImportLocation};
+use crate::syntax::Span;
+use crate::Typed;
+
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct ImportId(usize);
+#[derive(Debug, Copy, Clone, PartialEq, Eq, Hash)]
+pub struct ImportResultId(usize);
+
+struct StoredImport {
+    base_location: ImportLocation,
+    import: Import,
+    span: Span,
+    result: OnceCell<ImportResultId>,
+}
+
+#[derive(Default)]
+struct CtxtS {
+    imports: FrozenVec<Box<StoredImport>>,
+    import_results: FrozenVec<Box<Typed>>,
+}
+
+/// Context for the dhall compiler. Stores various global maps.
+#[derive(Copy, Clone)]
+pub struct Ctxt<'cx>(&'cx CtxtS);
+
+impl Ctxt<'_> {
+    pub fn with_new<T>(f: impl for<'cx> FnOnce(Ctxt<'cx>) -> T) -> T {
+        let cx = CtxtS::default();
+        let cx = Ctxt(&cx);
+        f(cx)
+    }
+}
+impl<'cx> Ctxt<'cx> {
+    fn get_stored_import(self, import: ImportId) -> &'cx StoredImport {
+        self.0.imports.get(import.0).unwrap()
+    }
+    pub fn get_import_result(self, id: ImportResultId) -> &'cx Typed {
+        &self.0.import_results.get(id.0).unwrap()
+    }
+
+    /// Store an import and the location relative to which it must be resolved.
+    pub fn push_import(
+        self,
+        base_location: ImportLocation,
+        import: Import,
+        span: Span,
+    ) -> ImportId {
+        let stored = StoredImport {
+            base_location,
+            import,
+            span,
+            result: OnceCell::new(),
+        };
+        let id = self.0.imports.len();
+        self.0.imports.push(Box::new(stored));
+        ImportId(id)
+    }
+    /// Store the result of fetching an import.
+    pub fn push_import_result(self, res: Typed) -> ImportResultId {
+        let id = self.0.import_results.len();
+        self.0.import_results.push(Box::new(res));
+        ImportResultId(id)
+    }
+
+    pub fn get_import(self, import: ImportId) -> &'cx Import {
+        &self.get_stored_import(import).import
+    }
+    pub fn get_import_base_location(
+        self,
+        import: ImportId,
+    ) -> &'cx ImportLocation {
+        &self.get_stored_import(import).base_location
+    }
+    pub fn get_import_span(self, import: ImportId) -> Span {
+        self.get_stored_import(import).span.clone()
+    }
+    /// Get the result of fetching this import. Returns `None` if the result has not yet been
+    /// fetched.
+    pub fn get_result_of_import(self, import: ImportId) -> Option<&'cx Typed> {
+        let res = self.get_resultid_of_import(import)?;
+        Some(self.get_import_result(res))
+    }
+    /// Get the id of the result of fetching this import. Returns `None` if the result has not yet
+    /// been fetched.
+    pub fn get_resultid_of_import(
+        self,
+        import: ImportId,
+    ) -> Option<ImportResultId> {
+        self.get_stored_import(import).result.get().copied()
+    }
+    /// Store the result of fetching this import.
+    pub fn set_result_of_import(
+        self,
+        import: ImportId,
+        res: Typed,
+    ) -> ImportResultId {
+        let res = self.push_import_result(res);
+        self.set_resultid_of_import(import, res);
+        res
+    }
+    /// Store the result of fetching this import.
+    pub fn set_resultid_of_import(self, import: ImportId, res: ImportResultId) {
+        let _ = self.get_stored_import(import).result.set(res);
+    }
+}