+
+The following functions to collect value variables from patterns are
+copied from HsUtils, with one change: we also collect the dictionary
+bindings (pat_binds) from ConPatOut. We need them for cases like
+
+h :: Arrow a => Int -> a (Int,Int) Int
+h x = proc (y,z) -> case compare x y of
+ GT -> returnA -< z+x
+
+The type checker turns the case into
+
+ case compare x y of
+ GT { p77 = plusInt } -> returnA -< p77 z x
+
+Here p77 is a local binding for the (+) operation.
+
+See comments in HsUtils for why the other version does not include
+these bindings.
+
+\begin{code}
+collectPatBinders :: OutputableBndr a => LPat a -> [a]
+collectPatBinders pat = map unLoc (collectLocatedPatBinders pat)
+
+collectLocatedPatBinders :: OutputableBndr a => LPat a -> [Located a]
+collectLocatedPatBinders pat = collectl pat []
+
+collectPatsBinders :: OutputableBndr a => [LPat a] -> [a]
+collectPatsBinders pats = map unLoc (collectLocatedPatsBinders pats)
+
+collectLocatedPatsBinders :: OutputableBndr a => [LPat a] -> [Located a]
+collectLocatedPatsBinders pats = foldr collectl [] pats
+
+---------------------
+collectl :: OutputableBndr a => LPat a -> [Located a] -> [Located a]
+collectl (L l pat) bndrs
+ = go pat
+ where
+ go (VarPat var) = L l var : bndrs
+ go (VarPatOut var bs) = L l var : collectHsBindLocatedBinders bs
+ ++ bndrs
+ go (WildPat _) = bndrs
+ go (LazyPat pat) = collectl pat bndrs
+ go (BangPat pat) = collectl pat bndrs
+ go (AsPat a pat) = a : collectl pat bndrs
+ go (ParPat pat) = collectl pat bndrs
+
+ go (ListPat pats _) = foldr collectl bndrs pats
+ go (PArrPat pats _) = foldr collectl bndrs pats
+ go (TuplePat pats _ _) = foldr collectl bndrs pats
+
+ go (ConPatIn _ ps) = foldr collectl bndrs (hsConPatArgs ps)
+ go (ConPatOut {pat_args=ps, pat_binds=ds}) =
+ collectHsBindLocatedBinders ds
+ ++ foldr collectl bndrs (hsConPatArgs ps)
+ go (LitPat _) = bndrs
+ go (NPat _ _ _) = bndrs
+ go (NPlusKPat n _ _ _) = n : bndrs
+
+ go (SigPatIn pat _) = collectl pat bndrs
+ go (SigPatOut pat _) = collectl pat bndrs
+ go (TypePat _) = bndrs
+ go (CoPat _ pat _) = collectl (noLoc pat) bndrs
+ go p = pprPanic "collectl/go" (ppr p)
+\end{code}