More consistent behavior for typeVars and substType with regards …

…to binders. (#67)

CHANGELOG.markdown

@@ -1,3 +1,8 @@
+3.0.3
+-----
+* Refined the behavior of `substType` in `Control.Lens.TH` to match the behavior of `typeVarsEx` when moving under binders.
+
+
 3.0.2
 -----
 * Added `generateSignatures` option to `Control.Lens.TH` to allow the end user to disable the generation of type signatures for the

lens.cabal

@@ -1,6 +1,6 @@
 name:          lens
 category:      Data, Lenses
-version:       3.0.2
+version:       3.0.3
 license:       BSD3
 cabal-version: >= 1.8
 license-file:  LICENSE

src/Language/Haskell/TH/Lens.hs

@@ -28,6 +28,7 @@ module Language.Haskell.TH.Lens
 import Control.Applicative
 import Control.Lens.Getter
 import Control.Lens.Setter
+import Control.Lens.Fold
 import Control.Lens.Type
 import Control.Lens.Traversal
 import Control.Lens.IndexedLens
@@ -104,7 +105,8 @@ class SubstType t where
 
 instance SubstType Type where
   substType m t@(VarT n)          = fromMaybe t (m^.at n)
-  substType m (ForallT bs ctx ty) = ForallT bs (substType m ctx) (substType m ty)
+  substType m (ForallT bs ctx ty) = ForallT bs (substType m' ctx) (substType m' ty)
+    where m' = foldrOf typeVars Map.delete m bs
   substType m (SigT t k)          = SigT (substType m t) k
   substType m (AppT l r)          = AppT (substType m l) (substType m r)
   substType _ t                   = t