Add Hir as untyped alternative to TyExpr

5 files changed, 133 insertions, 65 deletions

diff --git a/dhall/src/semantics/hir.rs b/dhall/src/semantics/hir.rs
new file mode 100644
index 0000000..2784ecb
--- /dev/null
+++ b/dhall/src/semantics/hir.rs
@@ -0,0 +1,112 @@
+#![allow(dead_code)]
+use crate::semantics::{rc, NameEnv, NzEnv, TyEnv, Value};
+use crate::syntax::{ExprKind, Span, V};
+use crate::{Normalized, NormalizedExpr, ToExprOptions};
+
+/// Stores an alpha-normalized variable.
+#[derive(Debug, Clone, Copy)]
+pub struct AlphaVar {
+    idx: usize,
+}
+
+#[derive(Debug, Clone)]
+pub(crate) enum HirKind {
+    Var(AlphaVar),
+    // Forbidden ExprKind variants: Var, Import, Embed
+    Expr(ExprKind<Hir, Normalized>),
+}
+
+// An expression with resolved variables and imports.
+#[derive(Debug, Clone)]
+pub(crate) struct Hir {
+    kind: Box<HirKind>,
+    span: Span,
+}
+
+impl AlphaVar {
+    pub(crate) fn new(idx: usize) -> Self {
+        AlphaVar { idx }
+    }
+    pub(crate) fn idx(&self) -> usize {
+        self.idx
+    }
+}
+
+impl Hir {
+    pub fn new(kind: HirKind, span: Span) -> Self {
+        Hir {
+            kind: Box::new(kind),
+            span,
+        }
+    }
+
+    pub fn kind(&self) -> &HirKind {
+        &*self.kind
+    }
+    pub fn span(&self) -> Span {
+        self.span.clone()
+    }
+
+    /// Converts a HIR expr back to the corresponding AST expression.
+    pub fn to_expr(&self, opts: ToExprOptions) -> NormalizedExpr {
+        hir_to_expr(self, opts, &mut NameEnv::new())
+    }
+    pub fn to_expr_tyenv(&self, env: &TyEnv) -> NormalizedExpr {
+        let opts = ToExprOptions {
+            normalize: true,
+            alpha: false,
+        };
+        let mut env = env.as_nameenv().clone();
+        hir_to_expr(self, opts, &mut env)
+    }
+
+    /// Eval the Hir. It will actually get evaluated only as needed on demand.
+    pub fn eval(&self, env: &NzEnv) -> Value {
+        // Value::new_thunk(env, self.clone())
+        todo!()
+    }
+    /// Eval a closed Hir (i.e. without free variables). It will actually get evaluated only as
+    /// needed on demand.
+    pub fn eval_closed_expr(&self) -> Value {
+        self.eval(&NzEnv::new())
+    }
+    /// Eval a closed Hir fully and recursively (TODO: ish, need to fix under lambdas)
+    pub fn rec_eval_closed_expr(&self) -> Value {
+        let mut val = self.eval_closed_expr();
+        val.normalize_mut();
+        val
+    }
+}
+
+fn hir_to_expr(
+    hir: &Hir,
+    opts: ToExprOptions,
+    env: &mut NameEnv,
+) -> NormalizedExpr {
+    rc(match hir.kind() {
+        HirKind::Var(v) if opts.alpha => ExprKind::Var(V("_".into(), v.idx())),
+        HirKind::Var(v) => ExprKind::Var(env.label_var(v)),
+        HirKind::Expr(e) => {
+            let e = e.map_ref_maybe_binder(|l, hir| {
+                if let Some(l) = l {
+                    env.insert_mut(l);
+                }
+                let e = hir_to_expr(hir, opts, env);
+                if let Some(_) = l {
+                    env.remove_mut();
+                }
+                e
+            });
+
+            match e {
+                ExprKind::Lam(_, t, e) if opts.alpha => {
+                    ExprKind::Lam("_".into(), t, e)
+                }
+                ExprKind::Pi(_, t, e) if opts.alpha => {
+                    ExprKind::Pi("_".into(), t, e)
+                }
+                e => e,
+            }
+        }
+    })
+}
diff --git a/dhall/src/semantics/mod.rs b/dhall/src/semantics/mod.rs
index 98fdf5a..a8c0659 100644
--- a/dhall/src/semantics/mod.rs
+++ b/dhall/src/semantics/mod.rs
@@ -1,8 +1,10 @@
 pub mod builtins;
+pub mod hir;
 pub mod nze;
 pub mod parse;
 pub mod resolve;
 pub mod tck;
 pub(crate) use self::builtins::*;
+pub(crate) use self::hir::*;
 pub(crate) use self::nze::*;
 pub(crate) use self::tck::*;
diff --git a/dhall/src/semantics/nze/normalize.rs b/dhall/src/semantics/nze/normalize.rs
index c660fce..b5949f5 100644
--- a/dhall/src/semantics/nze/normalize.rs
+++ b/dhall/src/semantics/nze/normalize.rs
@@ -3,8 +3,8 @@ use std::collections::HashMap;
 
 use crate::semantics::NzEnv;
 use crate::semantics::{
-    Binder, BuiltinClosure, Closure, TextLit, TyExpr, TyExprKind, Value,
-    ValueKind,
+    Binder, BuiltinClosure, Closure, Hir, HirKind, TextLit, TyExpr, TyExprKind,
+    Value, ValueKind,
 };
 use crate::syntax::{BinOp, Builtin, ExprKind, InterpolatedTextContents};
 use crate::Normalized;
diff --git a/dhall/src/semantics/nze/value.rs b/dhall/src/semantics/nze/value.rs
index 47c50a4..d4213bc 100644
--- a/dhall/src/semantics/nze/value.rs
+++ b/dhall/src/semantics/nze/value.rs
@@ -5,8 +5,8 @@ use crate::error::{TypeError, TypeMessage};
 use crate::semantics::nze::lazy;
 use crate::semantics::{
     apply_any, normalize_one_layer, normalize_tyexpr_whnf, squash_textlit,
-    type_with, Binder, BuiltinClosure, NzEnv, NzVar, TyEnv, TyExpr, TyExprKind,
-    VarEnv,
+    type_with, Binder, BuiltinClosure, Hir, NzEnv, NzVar, TyEnv, TyExpr,
+    TyExprKind, VarEnv,
 };
 use crate::syntax::{
     BinOp, Builtin, Const, ExprKind, Integer, InterpolatedTextContents, Label,
@@ -461,19 +461,19 @@ impl ValueKind {
 }
 
 impl Thunk {
-    pub fn new(env: &NzEnv, body: TyExpr) -> Self {
+    fn new(env: &NzEnv, body: TyExpr) -> Self {
         Thunk::Thunk {
             env: env.clone(),
             body,
         }
     }
-    pub fn from_partial_expr(
+    fn from_partial_expr(
         env: NzEnv,
         expr: ExprKind<Value, Normalized>,
     ) -> Self {
         Thunk::PartialExpr { env, expr }
     }
-    pub fn eval(self) -> ValueKind {
+    fn eval(self) -> ValueKind {
         match self {
             Thunk::Thunk { env, body } => normalize_tyexpr_whnf(&body, &env),
             Thunk::PartialExpr { env, expr } => normalize_one_layer(expr, &env),
diff --git a/dhall/src/semantics/tck/tyexpr.rs b/dhall/src/semantics/tck/tyexpr.rs
index 1886646..fa578c0 100644
--- a/dhall/src/semantics/tck/tyexpr.rs
+++ b/dhall/src/semantics/tck/tyexpr.rs
@@ -1,17 +1,13 @@
 use crate::error::{TypeError, TypeMessage};
-use crate::semantics::{rc, NameEnv, NzEnv, TyEnv, Value};
+use crate::semantics::{
+    rc, AlphaVar, Hir, HirKind, NameEnv, NzEnv, TyEnv, Value,
+};
 use crate::syntax::{ExprKind, Span, V};
 use crate::Normalized;
 use crate::{NormalizedExpr, ToExprOptions};
 
 pub(crate) type Type = Value;
 
-/// Stores an alpha-normalized variable.
-#[derive(Debug, Clone, Copy)]
-pub struct AlphaVar {
-    idx: usize,
-}
-
 #[derive(Debug, Clone)]
 pub(crate) enum TyExprKind {
     Var(AlphaVar),
@@ -27,15 +23,6 @@ pub(crate) struct TyExpr {
     span: Span,
 }
 
-impl AlphaVar {
-    pub(crate) fn new(idx: usize) -> Self {
-        AlphaVar { idx }
-    }
-    pub(crate) fn idx(&self) -> usize {
-        self.idx
-    }
-}
-
 impl TyExpr {
     pub fn new(kind: TyExprKind, ty: Option<Type>, span: Span) -> Self {
         TyExpr {
@@ -58,17 +45,19 @@ impl TyExpr {
         }
     }
 
+    pub fn to_hir(&self) -> Hir {
+        let kind = match self.kind() {
+            TyExprKind::Var(v) => HirKind::Var(v.clone()),
+            TyExprKind::Expr(e) => HirKind::Expr(e.map_ref(|tye| tye.to_hir())),
+        };
+        Hir::new(kind, self.span())
+    }
     /// Converts a value back to the corresponding AST expression.
     pub fn to_expr(&self, opts: ToExprOptions) -> NormalizedExpr {
-        tyexpr_to_expr(self, opts, &mut NameEnv::new())
+        self.to_hir().to_expr(opts)
     }
     pub fn to_expr_tyenv(&self, env: &TyEnv) -> NormalizedExpr {
-        let opts = ToExprOptions {
-            normalize: true,
-            alpha: false,
-        };
-        let mut env = env.as_nameenv().clone();
-        tyexpr_to_expr(self, opts, &mut env)
+        self.to_hir().to_expr_tyenv(env)
     }
 
     /// Eval the TyExpr. It will actually get evaluated only as needed on demand.
@@ -88,41 +77,6 @@ impl TyExpr {
     }
 }
 
-fn tyexpr_to_expr<'a>(
-    tyexpr: &'a TyExpr,
-    opts: ToExprOptions,
-    env: &mut NameEnv,
-) -> NormalizedExpr {
-    rc(match tyexpr.kind() {
-        TyExprKind::Var(v) if opts.alpha => {
-            ExprKind::Var(V("_".into(), v.idx()))
-        }
-        TyExprKind::Var(v) => ExprKind::Var(env.label_var(v)),
-        TyExprKind::Expr(e) => {
-            let e = e.map_ref_maybe_binder(|l, tye| {
-                if let Some(l) = l {
-                    env.insert_mut(l);
-                }
-                let e = tyexpr_to_expr(tye, opts, env);
-                if let Some(_) = l {
-                    env.remove_mut();
-                }
-                e
-            });
-
-            match e {
-                ExprKind::Lam(_, t, e) if opts.alpha => {
-                    ExprKind::Lam("_".into(), t, e)
-                }
-                ExprKind::Pi(_, t, e) if opts.alpha => {
-                    ExprKind::Pi("_".into(), t, e)
-                }
-                e => e,
-            }
-        }
-    })
-}
-
 impl std::fmt::Debug for TyExpr {
     fn fmt(&self, fmt: &mut std::fmt::Formatter<'_>) -> std::fmt::Result {
         let mut x = fmt.debug_struct("TyExpr");