partly improve coercions over constant lines

still needs a real quality check, or something, for stuff like
e : (x ≡ x : A) ⊢ coe (𝑖 ⇒ e @𝑖) x

lib/Quox/Whnf/Main.idr

@@ -90,7 +90,7 @@ CanWhnf Elim Interface.isRedexE where
             whnf defs ctx $
               CaseNat pi piIH (Ann val (dsub1 ty q) val.loc) ret zer suc caseLoc
       Right nn => pure $
-        Element (CaseNat pi piIH nat ret zer suc caseLoc) $ natnf `orNo` nn
+        Element (CaseNat pi piIH nat ret zer suc caseLoc) (natnf `orNo` nn)
 
   -- case [t] ∷ [π.A] return p ⇒ C of { [x] ⇒ u } ⇝
   --   u[t∷A/x] ∷ C[[t] ∷ [π.A]/p]
@@ -104,7 +104,7 @@ CanWhnf Elim Interface.isRedexE where
         Coe ty p q val _ =>
           boxCoe defs ctx pi ty p q val ret body caseLoc
       Right nb =>
-        pure $ Element (CaseBox pi box ret body caseLoc) $ boxnf `orNo` nb
+        pure $ Element (CaseBox pi box ret body caseLoc) (boxnf `orNo` nb)
 
   -- e : Eq (𝑗 ⇒ A) t u ⊢ e @0 ⇝ t ∷ A‹0/𝑗›
   -- e : Eq (𝑗 ⇒ A) t u ⊢ e @1 ⇝ u ∷ A‹1/𝑗›
@@ -127,7 +127,7 @@ CanWhnf Elim Interface.isRedexE where
           whnf defs ctx $
             ends (Ann (setLoc appLoc l) ty.zero appLoc)
                  (Ann (setLoc appLoc r) ty.one  appLoc) e
-        B {} => pure $ Element (DApp f p appLoc) $ fnf `orNo` ndlh `orNo` Ah
+        B {} => pure $ Element (DApp f p appLoc) (fnf `orNo` ndlh `orNo` Ah)
 
   -- e ∷ A ⇝ e
   whnf defs ctx (Ann s a annLoc) = do
@@ -136,22 +136,28 @@ CanWhnf Elim Interface.isRedexE where
       Left  _  => let E e = s in pure $ Element e $ noOr2 snf
       Right ne => do
         Element a anf <- whnf defs ctx a
-        pure $ Element (Ann s a annLoc) $ ne `orNo` snf `orNo` anf
+        pure $ Element (Ann s a annLoc) (ne `orNo` snf `orNo` anf)
 
-  whnf defs ctx (Coe (S _ (N ty)) _ _ val coeLoc) =
-    whnf defs ctx $ Ann val ty coeLoc
-  whnf defs ctx (Coe (S [< i] (Y ty)) p q val coeLoc) =
-    case p `decEqv` q of
-      Yes y   => whnf defs ctx $ Ann val (ty // one q) coeLoc
-      No  npq => do
-        Element ty tynf <- whnf defs (extendDim i ctx) ty
-        case nchoose $ canPushCoe ty val of
-          Left y =>
-            pushCoe defs ctx i ty p q val coeLoc
-          Right npc =>
-            -- [fixme] what about ty.zero = ty.one????
-            pure $ Element (Coe (SY [< i] ty) p q val coeLoc)
-                           (tynf `orNo` npc `orNo` notYesNo npq)
+  whnf defs ctx (Coe ty p q val coeLoc) =
+    --   𝑖 ∉ fv(A)
+    -- -------------------------------
+    --   coe (𝑖 ⇒ A) @p @q s ⇝ s ∷ A
+    --
+    -- [fixme] needs a real equality check between ty.zero and ty.one
+    case dsqueezed ty of
+      Right ty => whnf defs ctx $ Ann val ty coeLoc
+      Left ([< i], ty) =>
+        case p `decEqv` q of
+          -- coe (𝑖 ⇒ A) @p @p s ⇝ (s ∷ A‹p/𝑖›)
+          Yes _   => whnf defs ctx $ Ann val (ty // one p) coeLoc
+          No  npq => do
+            Element ty tynf <- whnf defs (extendDim i ctx) ty
+            case nchoose $ canPushCoe ty val of
+              Left pc =>
+                pushCoe defs ctx i ty p q val coeLoc
+              Right npc =>
+                pure $ Element (Coe (SY [< i] ty) p q val coeLoc)
+                               (tynf `orNo` npc `orNo` notYesNo npq)
 
   whnf defs ctx (Comp ty p q val r zero one compLoc) =
     case p `decEqv` q of
@@ -173,8 +179,9 @@ CanWhnf Elim Interface.isRedexE where
       Left  y  =>
         let Ann ty (TYPE u _) _ = ty in
         reduceTypeCase defs ctx ty u ret arms def tcLoc
-      Right nt => pure $
-        Element (TypeCase ty ret arms def tcLoc) (tynf `orNo` retnf `orNo` nt)
+      Right nt =>
+        pure $ Element (TypeCase ty ret arms def tcLoc)
+                       (tynf `orNo` retnf `orNo` nt)
 
   whnf defs ctx (CloE  (Sub el th)) = whnf defs ctx $ pushSubstsWith' id th el
   whnf defs ctx (DCloE (Sub el th)) = whnf defs ctx $ pushSubstsWith' th id el