diff --git a/src/Convert/NestPI.hs b/src/Convert/NestPI.hs
index 5525dd0..8b38d3f 100644
--- a/src/Convert/NestPI.hs
+++ b/src/Convert/NestPI.hs
@@ -78,13 +78,10 @@ addItems pis existingPIs (item : items) =
         addItems pis existingPIs (head itemsToAdd : item : items)
     where
         thisPI = execWriter $ collectPIsM item
-        runner f = execWriter $ collectNestedModuleItemsM f item
-        usedPIs = Set.unions $ map runner
-            [ collectStmtsM collectSubroutinesM
-            , collectTypesM $ collectNestedTypesM collectTypenamesM
-            , collectExprsM $ collectNestedExprsM collectExprIdentsM
-            , collectLHSsM  $ collectNestedLHSsM  collectLHSIdentsM
-            ]
+        usedPIs = execWriter $
+            traverseNestedModuleItemsM (traverseIdentsM writeIdent) item
+        writeIdent :: Identifier -> Writer Idents Identifier
+        writeIdent x = tell (Set.singleton x) >> return x
         neededPIs = Set.difference (Set.difference usedPIs existingPIs) thisPI
         itemsToAdd = map MIPackageItem $ Map.elems $
             Map.restrictKeys pis neededPIs
@@ -98,28 +95,66 @@ collectPIsM (MIPackageItem item) =
         ident -> tell $ Set.singleton ident
 collectPIsM _ = return ()
 
--- writes down the names of subroutine invocations
-collectSubroutinesM :: Stmt -> Writer Idents ()
-collectSubroutinesM (Subroutine (Ident f) _) = tell $ Set.singleton f
-collectSubroutinesM _ = return ()
+-- visits all identifiers in a module item
+traverseIdentsM :: Monad m => MapperM m Identifier -> MapperM m ModuleItem
+traverseIdentsM identMapper = traverseNodesM
+    (traverseExprIdentsM identMapper)
+    (traverseDeclIdentsM identMapper)
+    (traverseTypeIdentsM identMapper)
+    (traverseLHSIdentsM  identMapper)
+    (traverseStmtIdentsM identMapper)
 
--- writes down the names of function calls and identifiers
-collectExprIdentsM :: Expr -> Writer Idents ()
-collectExprIdentsM (Call (Ident x) _) = tell $ Set.singleton x
-collectExprIdentsM (Ident x)          = tell $ Set.singleton x
-collectExprIdentsM _ = return ()
+-- visits all identifiers in an expression
+traverseExprIdentsM :: Monad m => MapperM m Identifier -> MapperM m Expr
+traverseExprIdentsM identMapper = fullMapper
+    where
+        fullMapper = exprMapper >=> traverseSinglyNestedExprsM fullMapper
+        exprMapper (Call (Ident x) args) =
+            identMapper x >>= \x' -> return $ Call (Ident x') args
+        exprMapper (Ident x) = identMapper x >>= return . Ident
+        exprMapper other = return other
 
--- writes down the names of identifiers
-collectLHSIdentsM :: LHS -> Writer Idents ()
-collectLHSIdentsM (LHSIdent x) = tell $ Set.singleton x
-collectLHSIdentsM _ = return ()
+-- visits all identifiers in a type
+traverseTypeIdentsM :: Monad m => MapperM m Identifier -> MapperM m Type
+traverseTypeIdentsM identMapper = fullMapper
+    where
+        fullMapper = typeMapper
+            >=> traverseTypeExprsM (traverseExprIdentsM identMapper)
+            >=> traverseSinglyNestedTypesM fullMapper
+        typeMapper (Alias       x t) = aliasHelper (Alias      ) x t
+        typeMapper (PSAlias p   x t) = aliasHelper (PSAlias p  ) x t
+        typeMapper (CSAlias c p x t) = aliasHelper (CSAlias c p) x t
+        typeMapper other = return other
+        aliasHelper constructor x t =
+            identMapper x >>= \x' -> return $ constructor x' t
 
--- writes down aliased typenames
-collectTypenamesM :: Type -> Writer Idents ()
-collectTypenamesM (Alias       x _) = tell $ Set.singleton x
-collectTypenamesM (PSAlias _   x _) = tell $ Set.singleton x
-collectTypenamesM (CSAlias _ _ x _) = tell $ Set.singleton x
-collectTypenamesM _ = return ()
+-- visits all identifiers in an LHS
+traverseLHSIdentsM :: Monad m => MapperM m Identifier -> MapperM m LHS
+traverseLHSIdentsM identMapper = fullMapper
+    where
+        fullMapper = lhsMapper
+            >=> traverseLHSExprsM (traverseExprIdentsM identMapper)
+            >=> traverseSinglyNestedLHSsM fullMapper
+        lhsMapper (LHSIdent x) = identMapper x >>= return . LHSIdent
+        lhsMapper other = return other
+
+-- visits all identifiers in a statement
+traverseStmtIdentsM :: Monad m => MapperM m Identifier -> MapperM m Stmt
+traverseStmtIdentsM identMapper = fullMapper
+    where
+        fullMapper = stmtMapper
+            >=> traverseStmtExprsM (traverseExprIdentsM identMapper)
+            >=> traverseStmtLHSsM  (traverseLHSIdentsM  identMapper)
+            >=> traverseSinglyNestedStmtsM fullMapper
+        stmtMapper (Subroutine (Ident x) args) =
+            identMapper x >>= \x' -> return $ Subroutine (Ident x') args
+        stmtMapper other = return other
+
+-- visits all identifiers in a declaration
+traverseDeclIdentsM :: Monad m => MapperM m Identifier -> MapperM m Decl
+traverseDeclIdentsM identMapper =
+    traverseDeclExprsM (traverseExprIdentsM identMapper) >=>
+    traverseDeclTypesM (traverseTypeIdentsM identMapper)
 
 -- returns the "name" of a package item, if it has one
 piName :: PackageItem -> Identifier
diff --git a/src/Convert/Traverse.hs b/src/Convert/Traverse.hs
index 92b858b..eae33d0 100644
--- a/src/Convert/Traverse.hs
+++ b/src/Convert/Traverse.hs
@@ -26,6 +26,7 @@ module Convert.Traverse
 , traverseExprsM
 , traverseExprs
 , collectExprsM
+, traverseNodesM
 , traverseStmtExprsM
 , traverseStmtExprs
 , collectStmtExprsM
@@ -84,6 +85,9 @@ module Convert.Traverse
 , traverseSinglyNestedExprsM
 , traverseSinglyNestedExprs
 , collectSinglyNestedExprsM
+, traverseLHSExprsM
+, traverseLHSExprs
+, collectLHSExprsM
 , traverseNestedLHSsM
 , traverseNestedLHSs
 , collectNestedLHSsM
@@ -503,6 +507,11 @@ traverseLHSExprsM exprMapper =
             return $ LHSStream o e' ls
         lhsMapper other = return other
 
+traverseLHSExprs :: Mapper Expr -> Mapper LHS
+traverseLHSExprs = unmonad traverseLHSExprsM
+collectLHSExprsM :: Monad m => CollectorM m Expr -> CollectorM m LHS
+collectLHSExprsM = collectify traverseLHSExprsM
+
 mapBothM :: Monad m => MapperM m t -> MapperM m (t, t)
 mapBothM mapper (a, b) = do
     a' <- mapper a
@@ -510,14 +519,31 @@ mapBothM mapper (a, b) = do
     return (a', b')
 
 traverseExprsM :: Monad m => MapperM m Expr -> MapperM m ModuleItem
-traverseExprsM exprMapper = moduleItemMapper
+traverseExprsM exprMapper =
+    traverseNodesM exprMapper declMapper typeMapper lhsMapper stmtMapper
     where
-
     declMapper = traverseDeclExprsM exprMapper
     typeMapper = traverseNestedTypesM (traverseTypeExprsM exprMapper)
     lhsMapper = traverseNestedLHSsM (traverseLHSExprsM exprMapper)
     stmtMapper = traverseNestedStmtsM (traverseStmtExprsM exprMapper)
 
+traverseExprs :: Mapper Expr -> Mapper ModuleItem
+traverseExprs = unmonad traverseExprsM
+collectExprsM :: Monad m => CollectorM m Expr -> CollectorM m ModuleItem
+collectExprsM = collectify traverseExprsM
+
+traverseNodesM
+    :: Monad m
+    => MapperM m Expr
+    -> MapperM m Decl
+    -> MapperM m Type
+    -> MapperM m LHS
+    -> MapperM m Stmt
+    -> MapperM m ModuleItem
+traverseNodesM exprMapper declMapper typeMapper lhsMapper stmtMapper =
+    moduleItemMapper
+    where
+
     portBindingMapper (p, e) =
         exprMapper e >>= \e' -> return (p, e')
 
@@ -600,11 +626,6 @@ traverseExprsM exprMapper = moduleItemMapper
         e' <- exprMapper e
         return (dir, ident, e')
 
-traverseExprs :: Mapper Expr -> Mapper ModuleItem
-traverseExprs = unmonad traverseExprsM
-collectExprsM :: Monad m => CollectorM m Expr -> CollectorM m ModuleItem
-collectExprsM = collectify traverseExprsM
-
 traverseStmtExprsM :: Monad m => MapperM m Expr -> MapperM m Stmt
 traverseStmtExprsM exprMapper = flatStmtMapper
     where