diff --git a/parser/src/list_parser.rs b/parser/src/list_parser.rs
index 4996069..f8da430 100644
--- a/parser/src/list_parser.rs
+++ b/parser/src/list_parser.rs
@@ -9,13 +9,13 @@ use sym_parser::SymParser;
 
 #[derive(Debug)]
 pub struct ListParser {
-    list: Obj
+    list: Option<Pair>
 }
 
 impl ListParser {
     pub fn new() -> ListParser {
         ListParser {
-            list: Obj::Null
+            list: None
         }
     }
 }
@@ -25,12 +25,12 @@ impl NodeParser for ListParser {
         match lex.token() {
             Token::LeftParen => {
                 match self.list {
-                    Obj::Null => {
+                    None => {
                         // Create our empty pair and proceed parsing this list.
-                        self.list = Obj::new(Pair::empty());
+                        self.list = Some(Pair::empty());
                         NodeParseResult::Continue
                     },
-                    Obj::Ptr(_) => {
+                    Some(_) => {
                         // This is an embedded list. Create a new parser for it.
                         let parser = ListParser::new();
                         NodeParseResult::Push { next: Box::new(parser) }
@@ -42,7 +42,17 @@ impl NodeParser for ListParser {
                 NodeParseResult::Push { next: Box::new(parser) }
             },
             Token::RightParen => {
-                NodeParseResult::Complete { obj: self.list.take() }
+                match self.list {
+                    None => {
+                        let msg = format!("Found right paren without matching left paren");
+                        NodeParseResult::error(msg)
+                    },
+                    Some(_) => {
+                        let taken = self.list.take().unwrap();
+                        // TODO: If the cdr is Null, fill it in with an empty pair.
+                        NodeParseResult::Complete { obj: Obj::new(taken) }
+                    }
+                }
             }
         }
     }
@@ -51,4 +61,22 @@ impl NodeParser for ListParser {
         let msg = format!("Unmatched paren, found EOF");
         NodeParseResult::error(msg)
     }
+
+    fn subparser_completed(&mut self, obj: Obj) -> NodeParseResult {
+        if let Some(ref mut list) = self.list {
+            match list.car {
+                Obj::Null => {
+                    list.car = obj;
+                },
+                Obj::Ptr(_) => {
+                    let pair = Pair::with_car(obj);
+                    list.cdr = Obj::new(pair);
+                }
+            }
+            NodeParseResult::Continue
+        } else {
+            let msg = format!("what happened here???");
+            NodeParseResult::error(msg)
+        }
+    }
 }
diff --git a/parser/src/node_parser.rs b/parser/src/node_parser.rs
index fede135..ac9fa98 100644
--- a/parser/src/node_parser.rs
+++ b/parser/src/node_parser.rs
@@ -10,11 +10,9 @@ use sibiltypes::Obj;
 pub enum NodeParseResult {
     /// Continue parsing with this NodeParser. The passed in Lex was consumed.
     Continue,
-    /// This NodeParser has completed its work and has produced the given Object
-    /// as a result.
+    /// This NodeParser has completed its work and has produced the given Object as a result.
     Complete { obj: Obj },
-    /// Push a new NodeParser onto the parsing stack and let that parser proceed
-    /// with the current Lex.
+    /// Push a new NodeParser onto the parsing stack and let that parser proceed with the current Lex.
     Push { next: Box<NodeParser> },
     /// There was an error parsing with the current Lex.
     Error { msg: String },
@@ -26,13 +24,16 @@ impl NodeParseResult {
     }
 }
 
-/// A `NodeParser` is responsible for parsing one particular thing in the Scheme
-/// parse tree. Roughly, there should be one `XParser` for each variant of the
-/// `sibiltypes::Object` enum. As the top-level `Parser` object progresses
-/// through the stream of tokens, new NodeParsers are created to handle the
-/// nodes it encounters.
+/// A `NodeParser` is responsible for parsing one particular thing in the Scheme parse tree.
+/// Roughly, there should be one NodeParser for each type of object in `sibiltypes`. As the
+/// top-level `Parser` object progresses through the stream of tokens, new NodeParsers are created
+/// to handle the nodes it encounters.
 pub trait NodeParser: Debug {
+    /// Called on a NodeParser when a Lex is encountered in the input.
     fn parse(&mut self, lex: &Lex) -> NodeParseResult;
     /// Called on a NodeParser when None is encountered in the input.
     fn none(&mut self) -> NodeParseResult;
+    /// Called on a NodeParser when a NodeParser created by this one returns an object via
+    /// `NodeParseResult::Complete`.
+    fn subparser_completed(&mut self, obj: Obj) -> NodeParseResult;
 }
diff --git a/parser/src/program_parser.rs b/parser/src/program_parser.rs
index 665ae4f..d8ce16e 100644
--- a/parser/src/program_parser.rs
+++ b/parser/src/program_parser.rs
@@ -40,5 +40,9 @@ impl NodeParser for ProgramParser {
     fn none(&mut self) -> NodeParseResult {
         NodeParseResult::Complete { obj: Obj::Null }
     }
+
+    fn subparser_completed(&mut self, obj: Obj) -> NodeParseResult {
+        NodeParseResult::Complete { obj: obj }
+    }
 }
 
diff --git a/parser/src/sym_parser.rs b/parser/src/sym_parser.rs
index 7933884..cb51116 100644
--- a/parser/src/sym_parser.rs
+++ b/parser/src/sym_parser.rs
@@ -29,4 +29,9 @@ impl NodeParser for SymParser {
         let msg = format!("Expected symbol, found EOF");
         NodeParseResult::error(msg)
     }
+
+    fn subparser_completed(&mut self, obj: Obj) -> NodeParseResult {
+        let msg = format!("Unexpected parser result: {}", obj);
+        NodeParseResult::error(msg)
+    }
 }