--- Note [rnBndrLR]
--- ~~~~~~~~~~~~~~~
--- Notice that in rnBndrL, rnBndrR, we extend envR, envL respectively
--- with a binding [new_b -> new_b], where new_b is the new binder.
--- This is important when doing eta expansion; e.g. matching (\x.M) ~ N
--- In effect we switch to (\x'.M) ~ (\x'.N x'), where x' is new_b
--- So we must add x' to the env of both L and R. (x' is fresh, so it
--- can't capture anything in N.)
---
--- If we don't do this, we can get silly matches like
--- forall a. \y.a ~ v
--- succeeding with [x -> v y], which is bogus of course
+rnEtaL :: RnEnv2 -> Var -> (RnEnv2, Var)
+-- ^ Similar to 'rnBndrL' but used for eta expansion
+-- See Note [Eta expansion]
+rnEtaL (RV2 { envL = envL, envR = envR, in_scope = in_scope }) bL
+ = (RV2 { envL = extendVarEnv envL bL new_b
+ , envR = extendVarEnv envR new_b new_b -- Note [Eta expansion]
+ , in_scope = extendInScopeSet in_scope new_b }, new_b)
+ where
+ new_b = uniqAway in_scope bL
+
+rnEtaR :: RnEnv2 -> Var -> (RnEnv2, Var)
+-- ^ Similar to 'rnBndr2' but used for eta expansion
+-- See Note [Eta expansion]
+rnEtaR (RV2 { envL = envL, envR = envR, in_scope = in_scope }) bR
+ = (RV2 { envL = extendVarEnv envL new_b new_b -- Note [Eta expansion]
+ , envR = extendVarEnv envR bR new_b
+ , in_scope = extendInScopeSet in_scope new_b }, new_b)
+ where
+ new_b = uniqAway in_scope bR