Promote shift and subst_shift to traits

1 files changed, 45 insertions, 39 deletions

diff --git a/dhall/src/core/context.rs b/dhall/src/core/context.rs
index 0466058..e693317 100644
--- a/dhall/src/core/context.rs
+++ b/dhall/src/core/context.rs
@@ -6,7 +6,7 @@ use dhall_syntax::{Label, V};
 
 use crate::core::thunk::Thunk;
 use crate::core::value::Value;
-use crate::core::var::AlphaVar;
+use crate::core::var::{AlphaVar, Shift, Subst};
 use crate::phase::{Normalized, Type, Typed};
 
 #[derive(Debug, Clone)]
@@ -27,24 +27,6 @@ pub(crate) enum TyEnvItem {
 #[derive(Debug, Clone)]
 pub(crate) struct TypecheckContext(pub(crate) Context<Label, TyEnvItem>);
 
-impl NzEnvItem {
-    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        use NzEnvItem::*;
-        match self {
-            Thunk(e) => Thunk(e.shift(delta, var)),
-            Skip(v) => Skip(v.shift(delta, var)),
-        }
-    }
-
-    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
-        match self {
-            NzEnvItem::Thunk(e) => NzEnvItem::Thunk(e.subst_shift(var, val)),
-            NzEnvItem::Skip(v) if v == var => NzEnvItem::Thunk(val.to_thunk()),
-            NzEnvItem::Skip(v) => NzEnvItem::Skip(v.shift(-1, var)),
-        }
-    }
-}
-
 impl NormalizationContext {
     pub(crate) fn new() -> Self {
         NormalizationContext(Rc::new(Context::new()))
@@ -79,26 +61,6 @@ impl NormalizationContext {
         }
         NormalizationContext(Rc::new(ctx))
     }
-
-    pub(crate) fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        NormalizationContext(Rc::new(self.0.map(|_, e| e.shift(delta, var))))
-    }
-
-    pub(crate) fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
-        NormalizationContext(Rc::new(
-            self.0.map(|_, e| e.subst_shift(var, val)),
-        ))
-    }
-}
-
-impl TyEnvItem {
-    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
-        use TyEnvItem::*;
-        match self {
-            Type(v, e) => Type(v.shift(delta, var), e.shift(delta, var)),
-            Value(e) => Value(e.shift(delta, var)),
-        }
-    }
 }
 
 impl TypecheckContext {
@@ -127,6 +89,50 @@ impl TypecheckContext {
     }
 }
 
+impl Shift for NzEnvItem {
+    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        use NzEnvItem::*;
+        match self {
+            Thunk(e) => Thunk(e.shift(delta, var)),
+            Skip(v) => Skip(v.shift(delta, var)),
+        }
+    }
+}
+
+impl Shift for NormalizationContext {
+    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        NormalizationContext(Rc::new(self.0.map(|_, e| e.shift(delta, var))))
+    }
+}
+
+impl Shift for TyEnvItem {
+    fn shift(&self, delta: isize, var: &AlphaVar) -> Self {
+        use TyEnvItem::*;
+        match self {
+            Type(v, e) => Type(v.shift(delta, var), e.shift(delta, var)),
+            Value(e) => Value(e.shift(delta, var)),
+        }
+    }
+}
+
+impl Subst<Typed> for NzEnvItem {
+    fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        match self {
+            NzEnvItem::Thunk(e) => NzEnvItem::Thunk(e.subst_shift(var, val)),
+            NzEnvItem::Skip(v) if v == var => NzEnvItem::Thunk(val.to_thunk()),
+            NzEnvItem::Skip(v) => NzEnvItem::Skip(v.shift(-1, var)),
+        }
+    }
+}
+
+impl Subst<Typed> for NormalizationContext {
+    fn subst_shift(&self, var: &AlphaVar, val: &Typed) -> Self {
+        NormalizationContext(Rc::new(
+            self.0.map(|_, e| e.subst_shift(var, val)),
+        ))
+    }
+}
+
 impl PartialEq for TypecheckContext {
     fn eq(&self, _: &Self) -> bool {
         // don't count contexts when comparing stuff