Implement module loading and imports

crates/decodal-core/src/module.rs

@@ -0,0 +1,42 @@
+use alloc::string::String;
+
+use crate::{
+    Ast, ExprId, SourceForm, SourceId,
+    runtime::{EnvId, ThunkId},
+};
+
+#[derive(Debug, Clone)]
+pub struct Module {
+    pub key: String,
+    pub name: String,
+    pub source: SourceId,
+    pub ast: Ast,
+    pub root: ExprId,
+    pub source_form: SourceForm,
+    pub root_env: EnvId,
+    pub root_thunk: ThunkId,
+}
+
+#[derive(Debug, Clone)]
+pub struct LoadedSource {
+    pub key: String,
+    pub name: String,
+    pub source: String,
+}
+
+pub trait SourceLoader {
+    fn load(&mut self, current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedSource>;
+}
+
+#[derive(Debug, Clone, Copy, Default)]
+pub struct EmptyLoader;
+
+impl SourceLoader for EmptyLoader {
+    fn load(&mut self, _current_key: Option<&str>, specifier: &str) -> crate::Result<LoadedSource> {
+        Err(crate::Diagnostic::new(
+            crate::DiagnosticKind::Import,
+            crate::Span::default(),
+            alloc::format!("no source loader is configured for import `{specifier}`"),
+        ))
+    }
+}