Move envs to their own files

3 files changed, 89 insertions, 118 deletions

diff --git a/dhall/src/semantics/nze/env.rs b/dhall/src/semantics/nze/env.rs
new file mode 100644
index 0000000..203d99a
--- /dev/null
+++ b/dhall/src/semantics/nze/env.rs
@@ -0,0 +1,87 @@
+use crate::semantics::{AlphaVar, TyEnv, Value, ValueKind};
+
+#[derive(Debug, Clone, Copy, PartialEq, Eq)]
+pub(crate) enum NzVar {
+    /// Reverse-debruijn index: counts number of binders from the bottom of the stack.
+    Bound(usize),
+    /// Fake fresh variable generated for expression equality checking.
+    Fresh(usize),
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum NzEnvItem {
+    // Variable is bound with given type
+    Kept(Value),
+    // Variable has been replaced by corresponding value
+    Replaced(Value),
+}
+
+#[derive(Debug, Clone)]
+pub(crate) struct NzEnv {
+    items: Vec<NzEnvItem>,
+}
+
+impl NzVar {
+    pub fn new(idx: usize) -> Self {
+        NzVar::Bound(idx)
+    }
+    pub fn fresh() -> Self {
+        use std::sync::atomic::{AtomicUsize, Ordering};
+        // Global counter to ensure uniqueness of the generated id.
+        static FRESH_VAR_COUNTER: AtomicUsize = AtomicUsize::new(0);
+        let id = FRESH_VAR_COUNTER.fetch_add(1, Ordering::SeqCst);
+        NzVar::Fresh(id)
+    }
+    /// Get index of bound variable.
+    /// Panics on a fresh variable.
+    pub fn idx(&self) -> usize {
+        match self {
+            NzVar::Bound(i) => *i,
+            NzVar::Fresh(_) => panic!(
+                "Trying to use a fresh variable outside of equality checking"
+            ),
+        }
+    }
+}
+
+impl NzEnv {
+    pub fn new() -> Self {
+        NzEnv { items: Vec::new() }
+    }
+    pub fn to_alpha_tyenv(&self) -> TyEnv {
+        TyEnv::from_nzenv_alpha(self)
+    }
+
+    pub fn insert_type(&self, t: Value) -> Self {
+        let mut env = self.clone();
+        env.items.push(NzEnvItem::Kept(t));
+        env
+    }
+    pub fn insert_value(&self, e: Value) -> Self {
+        let mut env = self.clone();
+        env.items.push(NzEnvItem::Replaced(e));
+        env
+    }
+    pub fn lookup_val(&self, var: &AlphaVar) -> Value {
+        let idx = self.items.len() - 1 - var.idx();
+        match &self.items[idx] {
+            NzEnvItem::Kept(ty) => Value::from_kind_and_type_whnf(
+                ValueKind::Var(var.clone(), NzVar::new(idx)),
+                ty.clone(),
+            ),
+            NzEnvItem::Replaced(x) => x.clone(),
+        }
+    }
+
+    pub fn size(&self) -> usize {
+        self.items.len()
+    }
+}
+
+/// Ignore NzEnv when comparing; useful because we store them in `AppliedBuiltin`.
+impl std::cmp::PartialEq for NzEnv {
+    fn eq(&self, _other: &Self) -> bool {
+        true
+    }
+}
+impl std::cmp::Eq for NzEnv {}
diff --git a/dhall/src/semantics/nze/mod.rs b/dhall/src/semantics/nze/mod.rs
index 213404c..1cd2363 100644
--- a/dhall/src/semantics/nze/mod.rs
+++ b/dhall/src/semantics/nze/mod.rs
@@ -1,2 +1,2 @@
-pub mod nzexpr;
-pub(crate) use nzexpr::*;
+pub mod env;
+pub(crate) use env::*;
diff --git a/dhall/src/semantics/nze/nzexpr.rs b/dhall/src/semantics/nze/nzexpr.rs
deleted file mode 100644
index c065a5b..0000000
--- a/dhall/src/semantics/nze/nzexpr.rs
+++ /dev/null
@@ -1,116 +0,0 @@
-use crate::semantics::core::var::AlphaVar;
-use crate::syntax::{Label, V};
-
-pub(crate) type Binder = Label;
-
-#[derive(Debug, Clone)]
-pub(crate) struct NameEnv {
-    names: Vec<Binder>,
-}
-
-#[derive(Debug, Clone, Copy)]
-pub(crate) struct VarEnv {
-    size: usize,
-}
-
-#[derive(Debug, Clone, Copy, PartialEq, Eq)]
-pub(crate) enum NzVar {
-    /// Reverse-debruijn index: counts number of binders from the bottom of the stack.
-    Bound(usize),
-    /// Fake fresh variable generated for expression equality checking.
-    Fresh(usize),
-}
-
-impl NameEnv {
-    pub fn new() -> Self {
-        NameEnv { names: Vec::new() }
-    }
-    pub fn from_binders(names: impl Iterator<Item = Binder>) -> Self {
-        NameEnv {
-            names: names.collect(),
-        }
-    }
-    pub fn as_varenv(&self) -> VarEnv {
-        VarEnv {
-            size: self.names.len(),
-        }
-    }
-
-    pub fn insert(&self, x: &Binder) -> Self {
-        let mut env = self.clone();
-        env.insert_mut(x);
-        env
-    }
-    pub fn insert_mut(&mut self, x: &Binder) {
-        self.names.push(x.clone())
-    }
-    pub fn remove_mut(&mut self) {
-        self.names.pop();
-    }
-
-    pub fn unlabel_var(&self, var: &V<Binder>) -> 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<Binder> {
-        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 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 NzVar {
-    pub fn new(idx: usize) -> Self {
-        NzVar::Bound(idx)
-    }
-    pub fn fresh() -> Self {
-        use std::sync::atomic::{AtomicUsize, Ordering};
-        // Global counter to ensure uniqueness of the generated id.
-        static FRESH_VAR_COUNTER: AtomicUsize = AtomicUsize::new(0);
-        let id = FRESH_VAR_COUNTER.fetch_add(1, Ordering::SeqCst);
-        NzVar::Fresh(id)
-    }
-    // Panics on a fresh variable.
-    pub fn idx(&self) -> usize {
-        match self {
-            NzVar::Bound(i) => *i,
-            NzVar::Fresh(_) => panic!(
-                "Trying to use a fresh variable outside of equality checking"
-            ),
-        }
-    }
-}