Extract resolve-relevant envs together

1 files changed, 104 insertions, 0 deletions

diff --git a/dhall/src/semantics/resolve/env.rs b/dhall/src/semantics/resolve/env.rs
index e69de29..ff743d3 100644
--- a/dhall/src/semantics/resolve/env.rs
+++ b/dhall/src/semantics/resolve/env.rs
@@ -0,0 +1,104 @@
+use std::collections::HashMap;
+
+use crate::error::{Error, ImportError};
+use crate::semantics::{AlphaVar, Hir, Import, VarEnv};
+use crate::syntax::{Label, V};
+
+/// Environment for resolving names.
+#[derive(Debug, Clone)]
+pub(crate) struct NameEnv {
+    names: Vec<Label>,
+}
+
+pub(crate) type ImportCache = HashMap<Import, Hir>;
+pub(crate) type ImportStack = Vec<Import>;
+
+/// Environment for resolving imports
+#[derive(Debug, Clone)]
+pub(crate) struct ImportEnv {
+    cache: ImportCache,
+    stack: ImportStack,
+}
+
+impl NameEnv {
+    pub fn new() -> Self {
+        NameEnv { names: Vec::new() }
+    }
+    pub fn as_varenv(&self) -> VarEnv {
+        VarEnv::from_size(self.names.len())
+    }
+
+    pub fn insert(&self, x: &Label) -> Self {
+        let mut env = self.clone();
+        env.insert_mut(x);
+        env
+    }
+    pub fn insert_mut(&mut self, x: &Label) {
+        self.names.push(x.clone())
+    }
+    pub fn remove_mut(&mut self) {
+        self.names.pop();
+    }
+
+    pub fn unlabel_var(&self, var: &V) -> Option<AlphaVar> {
+        let V(name, idx) = var;
+        let (idx, _) = self
+            .names
+            .iter()
+            .rev()
+            .enumerate()
+            .filter(|(_, n)| *n == name)
+            .nth(*idx)?;
+        Some(AlphaVar::new(idx))
+    }
+    pub fn label_var(&self, var: &AlphaVar) -> V {
+        let name = &self.names[self.names.len() - 1 - var.idx()];
+        let idx = self
+            .names
+            .iter()
+            .rev()
+            .take(var.idx())
+            .filter(|n| *n == name)
+            .count();
+        V(name.clone(), idx)
+    }
+}
+
+impl ImportEnv {
+    pub fn new() -> Self {
+        ImportEnv {
+            cache: HashMap::new(),
+            stack: Vec::new(),
+        }
+    }
+
+    pub fn handle_import(
+        &mut self,
+        import: Import,
+        mut do_resolve: impl FnMut(&mut Self, &Import) -> Result<Hir, Error>,
+    ) -> Result<Hir, Error> {
+        if self.stack.contains(&import) {
+            return Err(
+                ImportError::ImportCycle(self.stack.clone(), import).into()
+            );
+        }
+        Ok(match self.cache.get(&import) {
+            Some(expr) => expr.clone(),
+            None => {
+                // Push the current import on the stack
+                self.stack.push(import.clone());
+
+                // Resolve the import recursively
+                let expr = do_resolve(self, &import)?;
+
+                // Remove import from the stack.
+                self.stack.pop();
+
+                // Add the import to the cache
+                self.cache.insert(import, expr.clone());
+
+                expr
+            }
+        })
+    }
+}