1 files changed, 137 insertions, 0 deletions
diff --git a/dhall/src/semantics/tck/env.rs b/dhall/src/semantics/tck/env.rs
new file mode 100644
index 0000000..32c2f21
--- /dev/null
+++ b/dhall/src/semantics/tck/env.rs
@@ -0,0 +1,137 @@
+use crate::semantics::{AlphaVar, NzEnv, NzVar, TyExprKind, Type, Value};
+use crate::syntax::{Label, V};
+
+/// Environment for indexing variables.
+#[derive(Debug, Clone, Copy)]
+pub(crate) struct VarEnv {
+    size: usize,
+}
+
+/// Environment for resolving names.
+#[derive(Debug, Clone)]
+pub(crate) struct NameEnv {
+    names: Vec<Label>,
+}
+
+/// Environment for typing expressions.
+#[derive(Debug, Clone)]
+pub(crate) struct TyEnv {
+    names: NameEnv,
+    items: NzEnv,
+}
+
+impl VarEnv {
+    pub fn new() -> Self {
+        VarEnv { size: 0 }
+    }
+    pub fn size(&self) -> usize {
+        self.size
+    }
+    pub fn insert(&self) -> Self {
+        VarEnv {
+            size: self.size + 1,
+        }
+    }
+    pub fn lookup(&self, var: &NzVar) -> AlphaVar {
+        self.lookup_fallible(var).unwrap()
+    }
+    pub fn lookup_fallible(&self, var: &NzVar) -> Option<AlphaVar> {
+        let idx = self.size.checked_sub(var.idx() + 1)?;
+        Some(AlphaVar::new(V((), idx)))
+    }
+}
+
+impl NameEnv {
+    pub fn new() -> Self {
+        NameEnv { names: Vec::new() }
+    }
+    pub fn from_binders(names: impl Iterator<Item = Label>) -> Self {
+        NameEnv {
+            names: names.collect(),
+        }
+    }
+    pub fn as_varenv(&self) -> VarEnv {
+        VarEnv {
+            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<Label>) -> Option<AlphaVar> {
+        let V(name, idx) = var;
+        let (idx, _) = self
+            .names
+            .iter()
+            .rev()
+            .enumerate()
+            .filter(|(_, n)| *n == name)
+            .nth(*idx)?;
+        Some(AlphaVar::new(V((), idx)))
+    }
+    pub fn label_var(&self, var: &AlphaVar) -> V<Label> {
+        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 TyEnv {
+    pub fn new() -> Self {
+        TyEnv {
+            names: NameEnv::new(),
+            items: NzEnv::new(),
+        }
+    }
+    pub fn from_nzenv_alpha(items: &NzEnv) -> Self {
+        TyEnv {
+            names: NameEnv::from_binders(
+                std::iter::repeat("_".into()).take(items.size()),
+            ),
+            items: items.clone(),
+        }
+    }
+    pub fn as_varenv(&self) -> VarEnv {
+        self.names.as_varenv()
+    }
+    pub fn as_nzenv(&self) -> &NzEnv {
+        &self.items
+    }
+    pub fn as_nameenv(&self) -> &NameEnv {
+        &self.names
+    }
+
+    pub fn insert_type(&self, x: &Label, t: Type) -> Self {
+        TyEnv {
+            names: self.names.insert(x),
+            items: self.items.insert_type(t),
+        }
+    }
+    pub fn insert_value(&self, x: &Label, e: Value) -> Self {
+        TyEnv {
+            names: self.names.insert(x),
+            items: self.items.insert_value(e),
+        }
+    }
+    pub fn lookup(&self, var: &V<Label>) -> Option<(TyExprKind, Type)> {
+        let var = self.names.unlabel_var(var)?;
+        let ty = self.items.lookup_val(&var).get_type().unwrap();
+        Some((TyExprKind::Var(var), ty))
+    }
+}