Finally get rid of all of the shift/subst_shift !

5 files changed, 3 insertions, 112 deletions

diff --git a/dhall/src/semantics/core/value.rs b/dhall/src/semantics/core/value.rs
index df1382b..90b30b4 100644
--- a/dhall/src/semantics/core/value.rs
+++ b/dhall/src/semantics/core/value.rs
@@ -256,27 +256,6 @@ impl Value {
             .expect("Internal type error: value is `Sort` but shouldn't be")
     }
 
-    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
-        Some(self.as_internal().shift(delta, var)?.into_value())
-    }
-    pub(crate) fn under_binder(&self) -> Self {
-        // Can't fail since delta is positive
-        self.shift(1, &AlphaVar::default()).unwrap()
-    }
-    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
-        match &*self.as_kind() {
-            // If the var matches, we can just reuse the provided value instead of copying it.
-            // We also check that the types match, if in debug mode.
-            ValueKind::Var(v, _) if v == var => {
-                if let Ok(self_ty) = self.get_type() {
-                    val.check_type(&self_ty.subst_shift(var, val));
-                }
-                val.clone()
-            }
-            _ => self.as_internal().subst_shift(var, val).into_value(),
-        }
-    }
-
     pub fn to_tyexpr(&self, venv: VarEnv) -> TyExpr {
         let tye = match &*self.as_kind() {
             // ValueKind::Var(v, _w) => TyExprKind::Var(*v),
@@ -487,27 +466,6 @@ impl ValueInternal {
             None => Err(TypeError::new(TypeMessage::Sort)),
         }
     }
-
-    fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
-        Some(ValueInternal {
-            form: self.form,
-            kind: self.kind.shift(delta, var)?,
-            ty: match &self.ty {
-                None => None,
-                Some(ty) => Some(ty.shift(delta, var)?),
-            },
-            span: self.span.clone(),
-        })
-    }
-    fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
-        ValueInternal {
-            // The resulting value may not stay in wnhf after substitution
-            form: Unevaled,
-            kind: self.kind.subst_shift(var, val),
-            ty: self.ty.as_ref().map(|x| x.subst_shift(var, val)),
-            span: self.span.clone(),
-        }
-    }
 }
 
 impl ValueKind<Value> {
@@ -588,36 +546,6 @@ impl ValueKind<Value> {
     pub(crate) fn from_builtin_env(b: Builtin, env: NzEnv) -> ValueKind<Value> {
         ValueKind::AppliedBuiltin(b, vec![], vec![], env)
     }
-
-    fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
-        Some(match self {
-            ValueKind::Var(v, w) if var.idx() <= v.idx() => {
-                ValueKind::Var(v.shift(delta, var)?, *w)
-            }
-            ValueKind::Var(v, w) => {
-                ValueKind::Var(v.shift(delta, var)?, w.shift(delta))
-            }
-            // ValueKind::Var(v, w) => ValueKind::Var(v.shift(delta, var)?, *w),
-            _ => self.traverse_ref_with_special_handling_of_binders(
-                |x| Ok(x.shift(delta, var)?),
-                |_, _, x| Ok(x.shift(delta, &var.under_binder())?),
-            )?,
-        })
-    }
-    fn subst_shift(&self, var: &AlphaVar, val: &Value) -> Self {
-        match self {
-            ValueKind::Var(v, _) if v == var => val.to_whnf_ignore_type(),
-            ValueKind::Var(v, w) => {
-                ValueKind::Var(v.shift(-1, var).unwrap(), *w)
-            }
-            _ => self.map_ref_with_special_handling_of_binders(
-                |x| x.subst_shift(var, val),
-                |_, _, x| {
-                    x.subst_shift(&var.under_binder(), &val.under_binder())
-                },
-            ),
-        }
-    }
 }
 
 impl<V> ValueKind<V> {
diff --git a/dhall/src/semantics/core/var.rs b/dhall/src/semantics/core/var.rs
index cf45d5e..3458489 100644
--- a/dhall/src/semantics/core/var.rs
+++ b/dhall/src/semantics/core/var.rs
@@ -29,16 +29,6 @@ impl AlphaVar {
     pub(crate) fn idx(&self) -> usize {
         self.alpha.idx()
     }
-
-    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Option<Self> {
-        Some(AlphaVar {
-            alpha: self.alpha.shift(delta, &var.alpha)?,
-        })
-    }
-    pub(crate) fn under_binder(&self) -> Self {
-        // Can't fail since delta is positive
-        self.shift(1, &AlphaVar::default()).unwrap()
-    }
 }
 
 impl Binder {
diff --git a/dhall/src/semantics/nze/nzexpr.rs b/dhall/src/semantics/nze/nzexpr.rs
index 87d0269..c065a5b 100644
--- a/dhall/src/semantics/nze/nzexpr.rs
+++ b/dhall/src/semantics/nze/nzexpr.rs
@@ -104,9 +104,6 @@ impl NzVar {
         let id = FRESH_VAR_COUNTER.fetch_add(1, Ordering::SeqCst);
         NzVar::Fresh(id)
     }
-    pub fn shift(&self, delta: isize) -> Self {
-        NzVar::new((self.idx() as isize + delta) as usize)
-    }
     // Panics on a fresh variable.
     pub fn idx(&self) -> usize {
         match self {
diff --git a/dhall/src/semantics/phase/normalize.rs b/dhall/src/semantics/phase/normalize.rs
index d40456b..fa80b6e 100644
--- a/dhall/src/semantics/phase/normalize.rs
+++ b/dhall/src/semantics/phase/normalize.rs
@@ -638,15 +638,13 @@ pub(crate) fn normalize_one_layer(
         ),
         // Those cases have already been completely handled in the typechecking phase (using
         // `RetWhole`), so they won't appear here.
-        ExprKind::Lam(_, _, _)
-        | ExprKind::Pi(_, _, _)
+        ExprKind::Lam(..)
+        | ExprKind::Pi(..)
+        | ExprKind::Let(..)
         | ExprKind::Embed(_)
         | ExprKind::Var(_) => {
             unreachable!("This case should have been handled in typecheck")
         }
-        ExprKind::Let(_, _, val, body) => {
-            Ret::Value(body.subst_shift(&AlphaVar::default(), &val))
-        }
         ExprKind::Annot(x, _) => Ret::Value(x),
         ExprKind::Const(c) => Ret::Value(const_to_value(c)),
         ExprKind::Builtin(b) => Ret::Value(builtin_to_value_env(b, env)),
diff --git a/dhall/src/syntax/ast/expr.rs b/dhall/src/syntax/ast/expr.rs
index 0da617b..424ac34 100644
--- a/dhall/src/syntax/ast/expr.rs
+++ b/dhall/src/syntax/ast/expr.rs
@@ -320,18 +320,6 @@ impl<E> Expr<E> {
     }
 }
 
-impl<Label: PartialEq + Clone> V<Label> {
-    pub(crate) fn shift(&self, delta: isize, var: &V<Label>) -> Option<Self> {
-        let V(x, n) = var;
-        let V(y, m) = self;
-        Some(if x == y && n <= m {
-            V(y.clone(), add_ui(*m, delta)?)
-        } else {
-            V(y.clone(), *m)
-        })
-    }
-}
-
 pub fn trivial_result<T>(x: Result<T, !>) -> T {
     match x {
         Ok(x) => x,
@@ -339,16 +327,6 @@ pub fn trivial_result<T>(x: Result<T, !>) -> T {
     }
 }
 
-/// Add an isize to an usize
-/// Returns `None` on over/underflow
-fn add_ui(u: usize, i: isize) -> Option<usize> {
-    Some(if i < 0 {
-        u.checked_sub(i.checked_neg()? as usize)?
-    } else {
-        u.checked_add(i as usize)?
-    })
-}
-
 impl PartialEq for NaiveDouble {
     fn eq(&self, other: &Self) -> bool {
         self.0.to_bits() == other.0.to_bits()